Abstract Background Chronic inflammatory cardiomyopathy (infl-CMP) is a long-term sequela caused by the chronicity of acute myocarditis, especially fulminant myocarditis (FM). Hydroxychloroquine (HCQ) may benefit these patients by inhibiting the excessive inflammatory response. Methods In this multicenter, randomized trial, we evaluated the efficacy and safety of HCQ in patients with chronic infl-CMP after FM. The primary outcome of the trial was a composite of the cardiovascular outcomes of time to cardiovascular death or heart transplant, hospitalization for heart failure or recurrence of myocarditis, permanent pacemaker, or implantable cardioverter defibrillator implantation. Secondary outcomes were changes in left ventricular ejection fraction (LVEF), left ventricular internal diastolic diameter (LVIDd), plasma levels of high-sensitivity cardiac troponin I (hs-cTnI), N-terminal pro-B-type natriuretic peptide (NT-proBNP), high-sensitivity C-reactive protein (hs-CRP), and erythrocyte sedimentation rate (ESR) from baseline to 12 months. Results Fifty patients were randomized to receive HCQ combined with prednisolone (PDN) or PDN monotherapy for 12 months. Compared to PDN monotherapy, HCQ combined with PDN therapy reduced the primary composite outcome [hazard ratio (HR) = 0.28, 95% confidence interval (CI) = 0.11–0.71] and had significant changes in the increase of LVEF and the decrease of LVIDd, hs-cTnI, NT-proBNP, and hs-CRP in patients with infl-CMP. No serious drug-related adverse events were recorded in either group, indicating an acceptable safety profile. Furthermore, HCQ combined with PDN significantly reduced the levels of 16 plasma cytokines to levels comparable to healthy controls. Conclusions Twelve months of HCQ combined with PDN therapy significantly improved the prognosis and heart function, inhibited inflammation, and had acceptable safety in patients with infl-CMP after FM. Trial registration ClinicalTrials.gov identifier: [42]NCT05961202. Graphical Abstract [43]graphic file with name 12916_2025_4301_Figa_HTML.jpg Supplementary Information The online version contains supplementary material available at 10.1186/s12916-025-04301-w. Keywords: Chronic inflammatory cardiomyopathy, Hydroxychloroquine, Randomized controlled trial, Efficacy, Safety Background Myocarditis is a primary inflammatory myocardial disease characterized by interstitial inflammatory cell infiltration and myocardial cell destruction [[44]1, [45]2]. Fulminant myocarditis (FM), comprising about 10% of patients diagnosed with acute myocarditis, is the most severe form of myocarditis, characterized by acute onset, rapid progression to cardiogenic shock, circulatory failure, or sudden death, with high in-hospital mortality and poor long-term prognosis [[46]3, [47]4]. Approximately 24% of patients with FM progressed to chronic inflammatory cardiomyopathy (infl-CMP), a long-term consequence of chronic myocarditis. This condition is characterized by left ventricular dilation, elevated plasma levels of troponin and N-terminal pro-B-type natriuretic peptide (NT-proBNP), or a hypokinetic non-dilated phenotype [[48]5]. Owing to the persistent or chronic inflammatory state of the myocardial tissue, patients with chronic infl-CMP typically present with symptoms and signs of chronic heart failure, often accompanied by myocardial injury and arrhythmia [[49]6, [50]7]. The pathophysiology involves over-inflammation and oxidative stress, which are critical in the genesis and progression of cardiovascular diseases like infl-CMP [[51]8]. Inflammatory markers such as C-reactive protein, interleukins, and tumor necrosis factor alpha serve important diagnostic and prognostic functions [[52]8]. Biomarkers like BNP, NT-proBNP, and ST2 are vital for predicting outcomes in advanced heart failure, providing insights into disease progression and patient survival [[53]9]. The diagnosis of infl-CMP relies mainly on histological evidence from endocardial myocardial biopsy [[54]5, [55]10]. Histologically, infl-CMP is characterized by focal or diffuse myocardial fibrosis with inflammatory cell infiltration [[56]6]. Clinical and basic studies on chronic infl-CMP are currently limited and insufficient to meet clinical needs. Although the clinical results of several studies have suggested a therapeutic effect of immunosuppressants (including glucocorticoids and azathioprine) [[57]11–[58]13], the therapeutic options for infl-CMP remain limited, particularly for those resulting from FM [[59]14]. The limited treatment options and the necessity for more effective therapies are emphasized in expert recommendations, which call for high-quality clinical trials to better evaluate the benefits and risks of new treatment approaches [[60]5]. Hydroxychloroquine (HCQ), a derivative of the heterocyclic aromatic compound quinoline, has been used clinically for more than 60 years [[61]15]. Although HCQ was originally developed to treat malaria, its immunomodulatory effects were accidentally discovered, which led to its subsequent widespread use in the treatment of rheumatic diseases, such as systemic lupus erythematosus and rheumatoid arthritis [[62]16, [63]17]. In addition, additional antiviral, metabolic, cardiovascular, antineoplastic, and antithrombotic effects of HCQ have been revealed [[64]18]. The effects of HCQ on the immune system have been systematically confirmed, including the inhibition of Toll-like receptor signals, inhibition of lymphocyte receptors, interference with lysosomal acidification and antigen presentation, binding and stabilization of DNA, and reduction of pro-inflammatory cytokines produced by macrophages [especially interleukin (IL)−1, IL-6, and tumor necrosis factor (TNF)-alpha] [[65]19]. Therefore, we speculated that HCQ may have therapeutic effects in patients with chronic infl-CMP. Based on the above background, we conducted a multicenter phase II randomized controlled clinical trial (the HYPIC study) to evaluate the efficacy and safety of HCQ combined with prednisolone (PDN), compared to that of PDN monotherapy, in the treatment of patients with chronic infl-CMP after FM. The primary objective of the HYPIC trial was to evaluate the effect of HCQ combined with PDN on composite cardiovascular outcomes, including cardiovascular death or heart transplant, hospitalization for heart failure or recurrence of myocarditis, permanent pacemaker use, or implantable cardioverter defibrillator (ICD) implantation after 12 months of treatment. The second objective focused on improving important clinical indicators, including cardiac function, myocardial injury, and inflammation levels. This study provides additional evidence and options for the treatment of patients with infl-CMP after FM and further fills the gap in the field of HCQ treatment for infl-CMP. Methods Study design This multicenter, open-label, evaluator-blinded, randomized controlled trial compared the therapeutic effects and safety of HCQ in patients with chronic infl-CMP after FM at two Chinese tertiary hospitals. The Clinical Trials and Follow-up Unit at Tongji Hospital was responsible for the data management and statistical analyses. The study protocol and statistical analysis plan are included in Additional file 1. The study was conducted in accordance with the principles of the Declaration of Helsinki and approved by the Research Ethics Committee of Tongji Medical College (date of vote: 27 October 2021, reference number: no. 2021-S148). Written informed consent was obtained from all patients. This trial was registered at ClinicalTrials.gov (identifier: [66]NCT05961202). Trial patients Patients aged 18–80 years diagnosed with chronic infl-CMP after FM, defined based on (i) left ventricular dysfunction [left ventricular ejection fraction (LVEF) < 50%] diagnosed using echocardiography (Simpson’s biplane) within 30 days before randomization; (ii) New York Heart Association (NYHA) class II–IV; (iii) chronic heart failure (lasting > 6 months) unresponsive to conventional supportive therapy with optimal therapeutic doses of an angiotensin-converting enzyme inhibitor (ACEI), angiotensin receptor blocker (ARB) or angiotensin receptor neprilysin inhibitor (ARNI), a β-blocker, and a mineralocorticoid receptor antagonist (MRA); (iv) high-sensitivity cardiac troponin I (hs-cTnI) > 26.2 pg/mL and NT-proBNP > 169 pg/mL; (v) diagnosed with confirmed FM for more than 3 months according to the Chinese expert consensus and guidelines on the diagnosis and treatment of fulminant myocarditis in adults [[67]20, [68]21]; (vi) diagnosed with chronic infl-CMP confirmed using myocardial biopsy; (vii) absence of cardiotropic viruses at polymerase chain reaction analysis; and (viii) volunteer for the study and written informed consent. The exclusion criteria were (i) age < 18 or > 80 years, (ii) confirmed or possible systemic inflammatory diseases, (iii) death or life expectancy of less than 1 year, (iv) drug or alcohol abuse, (v) pregnancy or lactation, (vi) allergy to hydroxychloroquine or derivatives of HCQ, (vii) history of prior permanent pacemaker or ICD implantation, (viii) history of sustained ventricular tachycardia, ventricular flutter, ventricular fibrillation, or high-degree of atrioventricular block requiring intervention, (ix) inability to take medication for various reasons, and (x) inability to provide informed consent. To be enrolled in the study, patients should meet all inclusion criteria and none of the exclusion criteria. Randomization and treatment allocation The participants were randomized using an automated interactive response technology system in a 1:1 ratio to receive HCQ combined with PDN therapy or PDN monotherapy. A mixed minimization and randomization approach was used to maintain a balance between the treatment groups for the vital baseline. All patients were required to receive the optimal therapeutic doses of standard heart drug therapy, including an ACEI, ARB or ARNI, a β-blocker, and an MRA, as per the guidelines for the diagnosis and treatment of heart failure in China [[69]22], for at least 3 months prior to enrollment, unless contraindications or intolerances existed. The enrolled patients were randomly assigned to receive oral HCQ (200 mg daily for 1 year) combined with PDN (20 mg daily for 1 year) (25 patients, HCQ combined with PDN therapy group) or PDN (20 mg daily for 1 year) alone (25 patients, PDN monotherapy group). Two hundred milligrams of HCQ per day provides anti-inflammatory effects while minimizing potential side effects [[70]23]. HCQ and PDN were administered as two separate pills twice daily. Patients then entered a 12-month treatment period, during which they were followed up via five in-person study visits (at 1, 3, 6, 9, and 12 months), during which time they underwent repeat physical examinations, laboratory assessments, echocardiography, and electrocardiogram examinations (at 1, 3, 6, 9, and 12 months). Outcomes The primary outcome of the study was the composite cardiovascular outcome of time to cardiovascular death or heart transplant, hospitalization for heart failure or recurrence of myocarditis, permanent pacemaker use, or ICD implantation. The secondary outcomes were changes in LVEF, left ventricular internal diastolic diameter (LVIDd), hs-cTnI, NT-proBNP, high-sensitivity C-reactive protein (hs-CRP), and erythrocyte sedimentation rate (ESR) from baseline to 12 months. The exploratory analyses included plasma inflammatory proteins from the Olink Target 96 inflammation panel. All follow-up physicians, echocardiologists, and blood test physicians were blinded to the clinical characteristics, treatment assignment, and outcomes. All the patients were blinded to the primary and secondary outcomes of the study. Safety was assessed by treatment-emergent adverse events (TEAEs), changes in the main vital signs (temperature, blood pressure, heart rate, and respiratory rate), 12-lead electrocardiogram, physical examination, and laboratory test results. All blood samples were analyzed by a clinical laboratory for safety (routine blood examination, biochemical examination, blood electrolytes, and coagulation). Treatment discontinuation was considered in cases of serious TEAEs including severe hypertension or hypotension, infectious diseases, leukopenia or neutropenia, allergy, retinopathy, and keratopathy. Plasma proteomics profiling Plasma from patients with chronic infl-CMP was analyzed using the Olink Inflammation Target 96 panel. Due to the unavailability of plasma samples from all enrolled patients during follow-up, we selected age- and sex-matched patients who had complete plasma samples at all three timepoints (baseline, 6 and 12 months). Specifically, 12 patients from the HCQ combined with PDN group and 12 from the PDN monotherapy group were systematically matched by age and sex. These samples, along with plasma from 16 healthy controls, were analyzed using the Olink multiplex proximity extension assay (Olink Proteomics, [71]www.olink.com) according to the manufacturer’s instructions. The Olink panel uses the proximity extension assay technology, which relies on pairs of DNA-labeled antibodies that bind to target proteins and generate unique reporter molecules that can be quantified by real-time polymerase chain reaction. The Olink panel provides normalized protein expression (NPX) units, which are log2-transformed values proportional to the protein concentration and are used to compare the expression levels of individual proteins under different conditions. One NPX difference was equal to doubling of the protein concentration. Statistical analyses Previous studies have shown that the 1-year incidence of composite cardiovascular events in patients with chronic infl-CMP is approximately 50% [[72]11, [73]24]. We estimated that 22 patients per group would provide 80% power to detect a statistically significant difference in the primary outcome between the groups, assuming a two-sided type I error rate of 0.05 and expected treatment success rates of 70% in the HCQ combined with PDN group and 40% in the PDN monotherapy group. Allowing for a 10% anticipated dropout rate, a total of 50 patients (25 per group) were targeted for enrollment. Eligible patients were randomized in a 1:1 ratio to receive either HCQ combined with PDN or PDN monotherapy, ensuring balanced allocation and objective study results. The distribution and homoscedasticity of each dataset were tested using D’Agostino’s and Pearson’s omnibus normality tests. Recognizing the small sample sizes, all continuous variables were reported as medians (interquartile range, IQR) and compared using the Wilcoxon rank-sum test. Categorical data are presented as n (percentage) and were compared using the chi-square test, Fisher’s exact test, and the Cochran–Mantel–Haenszel test, as appropriate. A two-sided P value of less than 0.05 was regarded as statistically significant. Kaplan–Meier curves were used to estimate the cumulative event rates in the two groups. Differences between groups were compared using log-rank tests. The Cox proportional hazards model was used to obtain hazard ratios (HR) for the outcomes. No imputation of missing values was performed in the study. All statistical analyses were performed using R (version 4.1.1; R Foundation for Statistics Computing, Vienna, Austria). Results Study participants Between November 2021 and May 2023, 72 patients with chronic infl-CMP after FM were screened, of which 50 qualified and were randomized 1:1. Among these patients, 25 received HCQ combined with PDN therapy, and 25 received PDN monotherapy (Fig. [74]1). Baseline characteristics were generally well balanced between the two groups (Table [75]1). Overall, the median age of all enrolled patients was 40.0 (IQR, 32.0–51.0) years, 46.0% were men, and 54.0% were women. The median body mass index (BMI) was 22.7 (IQR, 20.7–24.2) kg/m^2. The most common comorbidity was hypertension (24.0%). NYHA class II symptoms were present in 50%, with class III symptoms in 38%, and with class IV symptoms in 12%. The median LVEF was 41.0 (IQR, 37.0–43.0) %, and median LVIDd was 57.0 (IQR, 55.0–59.0) mm. Additionally, the median hs-cTnI was 288.8 (IQR, 187.0–436.4) pg/mL, median NT-proBNP was 1029.0 (IQR, 697.5–2002.0) pg/mL, median hs-CRP was 4.0 (IQR, 2.5–5.7) mg/L, and median ESR was 12.0 (IQR, 8.0–15.0) mm/H. The QRS duration, time from FM diagnosis to enrollment, and prior hospitalization for HF showed no significant differences between the two groups (all P > 0.05, Table [76]1). The use of concomitant guideline-directed medical therapy (GDMT) for heart failure was also well balanced between the two groups at baseline (all P > 0.05, Table [77]1), and after 12 months of treatment, there were still no significant differences in GDMT (all P > 0.05, Additional file 2: Table S1), thereby excluding the potential impact of other medication differences on the outcomes. Fig. 1. [78]Fig. 1 [79]Open in a new tab Trial flow chart Table 1. Baseline characteristics of patients with chronic inflammatory cardiomyopathy after fulminant myocarditis randomized to the hydroxychloroquine plus prednisolone group and the prednisolone monotherapy group All (n = 50) HCQ + PDN (n = 25) PDN monotherapy (n = 25) P value Age, years 40.0 (32.0–51.0) 40.0 (28.0–53.0) 40.0 (33.0–51.0) 0.90 Sex   Male, n (%) 23 (46.0) 11 (44.0) 12 (48.0) 0.78   Female, n (%) 27 (54.0) 14 (56.0) 13 (52.0) 0.78   Body mass index, kg/m^2 22.7 (20.7–24.2) 22.1 (20.4–24.0) 23.3 (21.5–24.3) 0.38   HR, bpm 75.0 (70.0–80.0) 78.0 (73.0–81.0) 75.0 (69.0–80.0) 0.31   SBP, mmHg 117.0 (110.0–125.0) 113.0 (110.0–119.0) 119.0 (110.0–127.0) 0.16   DBP, mmHg 73.0 (68.0–80.0) 71.0 (68.0–78.0) 78.0 (69.0–82.0) 0.38 Medical history   Smoking, n (%) 11 (22.0) 6 (24.0) 5 (20.0) 0.73   Drinking, n (%) 10 (20.0) 4 (16.0) 6 (24.0) 0.48   Hypertension^a, n (%) 12 (24.0) 7 (28.0) 5 (20.0) 0.51   Coronary heart disease^b, n (%) 11 (22.0) 4 (16.0) 7 (28.0) 0.31   Diabetes^c, n (%) 6 (12.0) 4 (16.0) 2 (8.0) 0.66   Hyperlipidemia^d, n (%) 8 (16.0) 3 (12.0) 5 (20.0) 0.70 NYHA class, n (%)   II 25 (50.0) 11 (44.0) 14 (56.0) 0.40   III 19 (38.0) 10 (40.0) 9 (36.0) 0.77   IV 6 (12.0) 4 (16.0) 2 (8.0) 0.66   LVEF, % 41.0 (37.0–43.0) 41.0 (36.0–43.0) 40.0 (39.0–43.0) 0.54   LVIDd, mm 57.0 (55.0–59.0) 56.0 (55.0–59.0) 57.0 (55.0–59.0) 0.89   hs-cTnI, pg/mL 288.8 (187.0–436.4) 305.4 (198.7–462.1) 253.5 (171.7–476.5) 0.36   NT-proBNP, pg/mL 1029.0 (697.5–2002.0) 1169.0 (722.0–2071.0) 946.0 (568.0–1801.0) 0.29   ALT, U/L 28.0 (22.0–37.0) 28.0 (22.0–40.0) 27.0 (21.0–37.0) 0.50   AST, U/L 33.0 (26.0–43.0) 36.0 (16.0–48.0) 31.0 (26.0–39.0) 0.47   eGFR, mL/min/1.73 m^2 94.1 (82.4–106.5) 93.5 (82.4–104.8) 97.1 (82.5–113.3) 0.46   hs-CRP, mg/L 4.0 (2.5–5.7) 4.3 (2.9–6.2) 3.9 (2.0–4.9) 0.31   ESR, mm/H 12.0 (8.0–15.0) 12.0 (9.0–16.0) 11.0 (8.0–15.0) 0.51   QRS duration, ms 83.0 (80.0–86.0) 83.0 (80.0–86.0) 83.0 (80.0–87.0) 0.88   Time from FM diagnosis to enrollment, months 12.0 (11.0–14.0) 12.0 (11.0–14.0) 12.0 (10.0–14.0) 0.35 Prior hospitalization for HF, times   0–1 41 (82.0) 20 80.0) 21 (84.0)  > 0.99   ≥ 2 9 (18.0) 5 (20.0) 4 (16.0)  > 0.99 Heart failure medication   ACEI/ARB/ARNI, n (%) 45 (90.0) 22 (88.0) 23 (92.0)  > 0.99   Beta-blockers, n (%) 46 (92.0) 23 (92.0) 23 (92.0)  > 0.99   Diuretics, n (%) 46 (92.0) 22 (88.0) 24 (96.0) 0.60   MRA, n (%) 42 (84.0) 22 (88.0) 20 (80.0) 0.70   Digoxin, n (%) 5 (10.0) 3 (12.0) 2 (8.0)  > 0.99   SGLT2i, n (%) 9 (18.0) 5 (20.0) 4 (16.0)  > 0.99 [80]Open in a new tab Continuous variables were presented as median and interquartile range (Q1–Q3) and were analyzed using the Wilcoxon rank-sum test HCQ hydroxychloroquine, PDN prednisolone, SBP systolic blood pressure, DBP diastolic blood pressure, NYHA New York Heart Association, LVEF left ventricular ejection fraction, LVIDd left ventricular internal diastolic diameter, AST aspartate aminotransferase, ALT alanine aminotransferase, hs-cTnI high-sensitivity cardiac troponin I, NT-proBNP, N-terminal-pro-B-type natriuretic peptide, eGFR, estimated glomerular filtration rate, hs-CRP high-sensitivity C-reactive protein, ESR erythrocyte sedimentation rate, HF heart failure, ACEI angiotensin-converting enzyme inhibitor, ARB angiotensin receptor blocker, ARNI angiotensin receptor neprilysin inhibitor, MRA mineralocorticoid receptor antagonist, SGLT2i sodium glucose cotransporter type 2 inhibitor ^aDefined as systolic/diastolic blood pressure ≥ 140/90 mm Hg ^bDefined as coronary artery stenosis exceeding 50% or complete occlusion found by coronary angiography ^cDefined as glycated hemoglobin (HbA1c) > 6.5% ^dDefined as baseline low-density lipoprotein cholesterol > 1.8 mmol/L with or without statin therapy One patient discontinued treatment due to heart transplant in the HCQ combined with PDN therapy group, and two patients discontinued treatment due to cardiovascular death in the PDN monotherapy group. No permanent treatment discontinuation occurred in any group for reasons other than death or heart transplant. Therefore, 24 patients in the HCQ combined with PDN therapy group and 23 patients in the PDN monotherapy group completed the trial on study medication, respectively. Safety follow-up was completed in all patients; no patients were lost to follow-up or withdrew consent, and the vital status was known in all patients with infl-CMP in both groups. Primary outcome The primary outcome was the composite cardiovascular outcome of time to cardiovascular death or heart transplant, hospitalization for heart failure or recurrence of myocarditis, permanent pacemaker use, or ICD implantation. Data for the primary outcomes were available for 50 (100%) patients with chronic infl-CMP at 12 months (25 patients in the HCQ combined with PDN therapy group and 25 patients in the PDN monotherapy group). During the 1-year follow-up, the composite cardiovascular outcome occurred in 21 (42.0%) patients: 6 (24.0%) in the HCQ combined with PDN therapy group and 15 (60.0%) in the PDN monotherapy group (Table [81]2). Patients in the HCQ combined with PDN therapy group had a significantly lower risk of the composite cardiovascular outcome compared with patients in the PDN monotherapy group [hazard ratio (HR) 0.28, 95% confidence interval (95% CI) 0.11 to 0.71; P = 0.008] (Table [82]2 and Fig. [83]2). The global Schoenfeld test indicated that the variables satisfied the Cox proportional hazards hypothesis (P = 0.26). Furthermore, we compared the incidence rates of hospitalization for heart failure and the recurrence of myocarditis, finding that the reduction in recurrence of myocarditis was greater than that for hospitalization for heart failure in the HCQ combined with PDN group (20.0% vs. 8%, Additional file 2: Table S2). Table 2. Primary outcomes at 12 months after treatment initiation HCQ + PDN (n = 25) PDN monotherapy (n = 25) HR (95% CI) P value Composite cardiovascular outcome 6 15 0.28 (0.11–0.71) 0.008 Cardiovascular death or heart transplant 1 2 0.02 (1.8E − 7–1356.0) 0.47 Hospitalization for HF or recurrence of myocarditis 5 12 0.32 (0.11–0.90) 0.03 Permanent pacemaker or ICD implantation 2 5 0.34 (0.07–1.77) 0.20 [84]Open in a new tab HF heart failure, ICD implantable cardioverter defibrillator Fig. 2. [85]Fig. 2 [86]Open in a new tab Primary outcome. A Incidence of the primary outcome. B Incidence of cardiovascular death or heart transplant. C Incidence of hospitalization for HF or myocarditis. D Incidence of permanent pacemaker or ICD implantation. Participants randomized to the HCQ combined with PDN therapy group are indicated in blue and those randomized to the PDN monotherapy group in red. Each of the graphs shows Kaplan–Meier curves with log-rank P values. HCQ, hydroxychloroquine; PDN, prednisolone; HF, heart failure; ICD, implantable cardioverter defibrillator Secondary outcomes The secondary outcomes were changes in LVEF, LVIDd, hs-cTnI, NT-proBNP, hs-CRP, and ESR from baseline to 12 months. The secondary outcomes were available for 47 (94.0%) patients with chronic infl-CMP after FM at 12 months (24 patients in the HCQ combined with PDN therapy group and 23 patients in the PDN monotherapy group). At baseline, the median LVEF (P = 0.80), LVIDd (P = 0.77), hs-cTnI (P = 0.41), NT-proBNP (P = 0.23), hs-CRP (P = 0.19), and ESR (P = 0.33) levels in the two groups of patients were comparable. The values of LVEF and LVIDd as well as the concentrations of hs-cTnI, NT-proBNP, hs-CRP, and ESR at baseline and after 1, 3, 6, 9, and 12 months of treatment are shown in Additional file 2: Fig. S1. We found significant decreases in the hs-cTnI and hs-CRP levels between the two groups during the first month after treatment. LVEF, NT-proBNP, and ESR showed significant improvement after 3 months of treatment. LVIDd decreased significantly after 6 months of treatment. After 12 months of treatment, LVIDd, hs-cTnI, NT-proBNP, and hs-CRP levels in the HCQ combined with PDN therapy group significantly improved from baseline and were significantly lower than those in the PDN monotherapy group (all P < 0.05), whereas LVEF significantly increased in the HCQ combined with PDN therapy group (P < 0.05) (Fig. [87]3). Similarly, compared with the PDN monotherapy group, there were significant decreases in LVIDd (P < 0.001), hs-cTnI (P = 0.037), NT-proBNP (P = 0.043), and hs-CRP (P = 0.007), and an increase in LVEF (P < 0.001) in the HCQ combined with PDN therapy group (Table [88]3). There was no significant difference in the decrease in ESR after 12 months of treatment between the two groups (P = 0.26). The estimated between-group differences (95% CI) in change in LVEF, LVIDd, hs-cTnI, NT-proBNP, hs-CRP, and ESR were 8.00 (5.00, 11.00), − 4.00 (− 6.00, − 2.00), − 98.40 (− 174.80, − 5.90), − 399.30 (− 877.00, − 14.00), − 1.65 (− 3.10, − 0.40), and − 2.00 (− 5.00, 1.00), respectively. Moreover, in the HCQ combined with PDN therapy group, LVEF recovery rates progressively increased from 8.0% in the first month to 83.3% by the twelfth month. In contrast, the PDN monotherapy group showed a consistently low recovery rate, ranging from 0.0% to 21.7% throughout the follow-up period. Results were highly consistent over time, with significant differences appearing from the third month onward (P = 0.03). The benefits of HCQ combined with PDN treatment persisted through months 6, 9, and 12 (P < 0.001), as detailed in Additional file 2: Table S3. Additionally, we compared the impact of prior heart failure hospitalizations on prognosis and found that patients with chronic infl-CMP who had experienced two or more previous heart failure hospitalizations showed a higher incidence of composite cardiovascular outcomes and a lower rate of LVEF recovery (Additional file 2: Table S4). Fig. 3. [89]Fig. 3 [90]Open in a new tab Comparison of clinical indicators in secondary outcomes. Box plots of the distribution of LVEF (A), LVIDd (B), hs-cTnI (C), NT-proBNP (D), hs-CRP (E), and ESR (F) at baseline and 12 months after treatment in the HCQ combined with PDN therapy group (dark blue) and the PDN monotherapy group (gray). LVEF, left ventricular ejection fraction; LVIDd, left ventricular internal diastolic diameter; hs-cTnI, high-sensitivity cardiac troponin I; NT-proBNP, N-terminal-pro-B-type natriuretic peptide; hs-CRP, high-sensitivity C-reactive protein; ESR; erythrocyte sedimentation rate Table 3. Secondary outcomes at 12 months after treatment initiation HCQ + PDN (n = 24) PDN monotherapy (n = 23) Estimated between-group difference (95% CI) P value Baseline 12 months change Baseline 12 months change LVEF, % 41.0 (36.0, 43.0) 11.0 (8.0, 15.0) 40.0 (38.0, 43.0) 3.0 (1.0, 5.0) 8.00 (5.00, 11.00)  < 0.001 LVIDd, mm 57.0 (55.0, 59.0)  − 3.0 (− 7.0, − 1.0) 56.0 (55.0, 58.0) 1.0 (0.0, 2.0)  − 4.00 (− 6.00, − 2.00)  < 0.001 hs-cTnI, pg/mL 308.8 (218.6, 487.8)  − 297.4 (− 467.5, − 211.0) 259.3 (177.3–550.2)  − 192.8 (− 317.4, − 135.9)  − 98.40 (− 174.80, − 5.90) 0.037 NT-proBNP, pg/mL 1156.0 (720.0, 2100.0)  − 951.5 (− 1977, − 541.0) 832.0 (544.0–1799.0)  − 517.0 (− 1240.0, − 186.0)  − 399.30 (− 877.00, − 14.00) 0.043 hs-CRP, mg/L 4.5 (2.8, 6.4)  − 4.3 (− 6.0, − 2.2) 3.3 (1.9–4.7)  − 2.0 (− 3.6, − 1.1)  − 1.65 (− 3.10, − 0.40) 0.007 ESR, mm/H 12.0 (8.0, 16.0)  − 10.0 (− 13.0, − 6.0) 10.0 (7.0, 15.0)  − 9.0 (− 11.0, − 5.0)  − 2.00 (− 5.00, 1.00) 0.26 [91]Open in a new tab Baseline data and change from baseline data are presented as median and interquartile range (Q1, Q3). Estimated between-group difference presented as median difference (95% CI) Safety and tolerability Similar incidences of investigator-reported TEAEs were observed between treatment groups (Table [92]4). TEAEs were reported by a total of 39 (78.0%) of the 50 subjects in the safety population: 18 (72.0%) subjects in the HCQ combined with PDN therapy group and 21 (84.0%) subjects in the PDN monotherapy group. Serious adverse events occurred in 10 patients (40.0%) in the HCQ combined with PDN therapy group and 17 (68.0%) in the PDN monotherapy group. During the study period, one patient (4.0%) with HCQ and PDN therapy received a heart transplant, and two patients (8.0%) with PDN monotherapy died of cardiac arrest (no medical history of coronary artery disease), which led to treatment discontinuation and were not judged as study drug-related. Most TEAEs were mild or moderate in intensity in both treatment groups. The most prevalent TEAEs were fatigue (HCQ and PDN: 44.0%; PDN monotherapy: 52.0%), dizziness (HCQ and PDN: 36.0%; PDN monotherapy: 28.0%), and dyspnea (HCQ and PDN: 16.0%; PDN monotherapy: 24.0%). For TEAEs of special interest, one patient (4.0%) in the PDN monotherapy group occurred non-fatal stroke that was assessed as unrelated to treatment. Moreover, three case of conduction disorders (12.0%), two case of QT interval prolongation (8.0%), one case of acute liver injury (4.0%), three cases of infection (12.0%), three cases of visual impairment (12.0%), and two cases of allergies (8.0%) occurred in the HCQ combined with PDN therapy group. Correspondingly, four cases of conduction disorders (16.0%), two case of QT interval prolongation (8.0%), two cases of acute liver injury (8.0%), three cases of infection (12.0%), two cases of visual impairment (8.0%), and four cases of allergies (16.0%) occurred in the PDN monotherapy group. Table 4. Safety analysis and adverse events Event, n (%) HCQ + PDN (n = 25) PDN monotherapy (n = 25) Any reported AEs^a 18 (72.0) 21 (84.0) Any serious AEs^b 10 (40.0) 17 (68.0) Serious AEs^b related to study drug 0 (0.0) 0 (0.0) Serious AEs^b leading to treatment discontinuation 1 (4.0) 2 (8.0) Most frequent AEs^c   Fatigue 11 (44.0) 13 (52.0)   Dizziness 9 (36.0) 7 (28.0)   Dyspnea 4 (16.0) 6 (24.0)   Cough 4 (12.0) 5 (20.0)   Headache 3 (12.0) 3 (12.0)   Diarrhea 3 (12.0) 2 (8.0) AEs of interest   All-cause death 0 (0.0) 2 (8.0)   Cardiovascular death 0 (0.0) 2 (8.0)   Nonfatal MI 0 (0.0) 0 (0.0)   Stroke 0 (0.0) 1 (4.0)   Conduction disorders 3 (12.0) 4 (16.0)   QT interval prolongation 2 (8.0) 2 (8.0)   Acute kidney injury 0 (0.0) 0 (0.0)   Acute liver injury 1 (4.0) 2 (8.0)   Infection 3 (12.0) 3 (12.0)   Visual impairment 3 (12.0) 2 (8.0)   Allergy 2 (8.0) 4 (16.0) [93]Open in a new tab AEs, adverse event ^aReported as treatment-emergent AEs relating to seriousness criteria ^bA treatment-emergent event was considered to be a serious AE if it: (i) resulted in death, (ii) was life-threatening, (iii) required inpatient hospitalization or prolongation of existing hospitalization, (iv) caused persistent or significant disability/incapacity, (v) was a congenital abnormality or birth defect, or (vi) was judged by the investigator to be a serious or important medical event ^cMost frequent AEs are sorted according to total frequency (except for AEs of interest). Cut-off: n ≥ 5 in total Exploratory outcomes Olink technology was used to quantify circulating inflammation-related proteins during treatment. We assessed plasma inflammation-related proteins in 24 patients with chronic infl-CMP after FM (12 in the HCQ combined with PDN therapy group and 12 in the PDN monotherapy group) at enrollment and 6 and 12 months after treatment, and compared them with 16 healthy controls (Additional file 2: Table S5). A total of 92 plasma proteins were quantified, of which 37 showed changes relative to the control group in patients with chronic infl-CMP, including families of interleukins, chemokines, transforming growth factors, and tumor necrosis factors (Additional file 2: Fig. S2). GO and KEGG enrichment analysis suggested that the occurrence of infl-CMP might be related to immune response activation, leukocyte chemotaxis, and cytokine-cytokine receptor interaction (Additional file 2: Fig. S2). After 12 months of treatment with HCQ combined with PDN, 16 plasma proteins significantly decreased to levels observed in healthy controls, while only 2 proteins (OSM and TGF-alpha) significantly decreased compared to baseline in the PDN monotherapy group (Fig. [94]4), which indicated that HCQ treatment might lead to a decrease in 14 plasma inflammatory proteins in addition to OSM and TGF-alpha. Therefore, we conducted a pathway enrichment analysis of the 14 proteins whose expression decreased after 12 months of treatment. The results showed that HCQ may exert therapeutic effects on chronic infl-CMP by inhibiting lymphocyte chemotaxis, regulating leukocyte migration, and inhibiting cytokine activity and cytokine-cytokine receptor interactions (Additional file 2: Fig. S3). Fig. 4. [95]Fig. 4 [96]Open in a new tab Analysis of plasma inflammatory proteins via Olink Target 96 inflammation panel. Abnormal proteins in chronic inflammatory cardiomyopathy regressed towards healthy levels after treatment for 12 months in at least one group of patients. HCQ + PDN, HCQ combined with PDN therapy group (dark blue); PDN, PDN monotherapy group (gray); CON, healthy controls (orange); IL8, interleukin-8; VEGFA, vascular endothelial growth factor A; CXCL11, C-X-C motif chemokine 11; IL-2RB, interleukin-2 receptor subunit beta; OSM, oncostatin-M; CCL4, C–C motif chemokine 4; IL18, interleukin-18; TGF-alpha, transforming growth factor alpha; MCP-4, monocyte chemotactic protein 4; TNFSF14, tumor necrosis factor ligand superfamily member 14; IL-18R1, interleukin-18 receptor 1; CCL3, C–C motif chemokine 3; CXCL10, C-X-C motif chemokine 10; CASP-8, caspase-8; ST1A1, sulfotransferase 1A1; ADA, adenosine deaminase. *P < 0.05, **P < 0.01, ***P < 0.001, ****P < 0.0001 Discussion In this multicenter, open-label, evaluator-blinded, randomized controlled trial, we evaluated the efficacy and safety of HCQ combined with PDN therapy on the clinical outcomes of patients with chronic infl-CMP after FM. Compared with the PDN monotherapy group, the cardiovascular composite outcomes of time to cardiovascular death or heart transplant, hospitalization for heart failure or recurrence of myocarditis, and permanent pacemaker or ICD implantation, as well as important clinical indicators (LVEF, LVIDd, hs-cTnI, NT-proBNP, and hs-CRP), improved at 12 months in the HCQ group of patients. The magnitude of these benefits is clinically and statistically significant. Moreover, according to the results of Olink proteomics, 16 plasma inflammatory proteins in patients with chronic infl-CMP after FM significantly decreased to normal levels after 12 months of HCQ and PDN treatment (only two decreased in the PDN monotherapy group). Similarly, the incidence of adverse events was comparable between the two groups. To the best of our knowledge, the HYPIC study is the first clinical trial to demonstrate these significant benefits of HCQ combined with PDN therapy on the clinical outcomes of patients with chronic infl-CMP after FM, which suggests that such patients may benefit significantly from the administration of HCQ. These findings highlight the potential of HCQ combined with PDN as an effective therapeutic strategy for managing chronic infl-CMP following FM, offering a promising alternative to existing treatment options. Previous studies have shown that 47% of patients with acute or fulminant myocarditis do not recover to normal LVEF after 2 years of standard heart failure treatment [[97]10]. A substantial proportion of patients with myocarditis eventually develop chronic infl-CMP [[98]14, [99]25]. Patients with chronic infl-CMP have poor prognosis, with a 5-year survival rate of only 52.7%–70.3%, and urgently require standardized and effective treatment [[100]25, [101]26]. Randomized controlled studies and meta-analyses have confirmed the effectiveness of glucocorticoids in the treatment of patients with chronic infl-CMP [[102]5, [103]10, [104]21, [105]27], but glucocorticoids combined with other immunosuppressants (such as azathioprine) may have better therapeutic effects on chronic infl-CMP [[106]11–[107]13]. The TIMIC study, the first prospective randomized study of chronic infl-CMP, revealed the benefits of immunosuppressive therapy (prednisone and azathioprine) in terms of short-term efficacy and long-term prognosis in patients with virus-negative infl-CMP [[108]11, [109]12]. Another prospective study of 114 patients with chronic myocarditis or infl-CMP showed the effectiveness and beneficial effects of immunosuppressive therapy, which improved LVEF lasting for a long-term period of time [[110]13]. A meta-analysis summarizing 16 studies also concluded that patients with chronic infl-CMP receiving immunomodulatory treatment had improved LVEF compared to the control group (HR, 16.65; 95% CI, 4.55–28.74; P = 0.007) [[111]25]. A clinical study involving 31 patients showed that methylprednisolone partially improved the cardiac function and inflammatory infiltration in patients with chronic myocarditis [[112]28]. However, existing clinical data on treatments for chronic infl-CMP, particularly beyond conventional immunosuppressants, remain scarce and often derive from small or observational studies [[113]29], highlighting the need for robust randomized trials like the present study. HCQ has been widely used in the treatment of malaria and rheumatic diseases as a potent anti-inflammatory agent and immunomodulator and is also the most common drug used to relieve acute and chronic inflammatory diseases [[114]30]. Multiple studies have shown that HCQ use is associated with a reduced risk of cardiovascular disease in patients with rheumatic diseases [[115]31–[116]33]. HCQ may also have therapeutic effects in diabetes, dyslipidemia, coagulation diseases, infectious diseases, coronary heart disease, arthritis, and malignant tumor [[117]34–[118]37]. The HYPIC study demonstrated the efficacy and safety of HCQ combined with PDN therapy for treating patients with chronic infl-CMP after FM. Similar to the results of azathioprine combined with prednisone immunosuppressive treatment in the TIMIC study [[119]11, [120]12], we found that HCQ combined with PDN treatment significantly reduced the incidence of cardiovascular composite outcomes and improved cardiac function in patients with chronic infl-CMP after 1 year. Moreover, the HYPIC study suggested that HCQ with PDN treatment significantly reduced hs-cTnI, NT-proBNP, and hs-CRP levels. Interestingly, it has been reported that heart failure patients with ≥ 2 previous hospitalizations due to heart failure have worse prognoses [[121]38]. We also found that patients with chronic infl-CMP who had ≥ 2 prior heart failure hospitalizations showed a higher incidence of composite cardiovascular outcomes and a lower LVEF recovery rate, highlighting the necessity to pay special attention to patients with a history of frequent heart failure hospitalizations. HCQ may have side effects, including gastrointestinal disorders, rashes, retinopathy, and arrhythmia [[122]39]. However, most experts believe that this tested and effective anti-inflammatory drug is safe and reassuring [[123]40]. A phase I trial of HCQ showed the safety and tolerability of HCQ [[124]41]. A randomized controlled trial also showed that HCQ combined with RAAS inhibition significantly reduced proteinuria in IgA nephropathy patients with 6 months without evidence of adverse events [[125]42]. In addition, a study demonstrated that HCQ does not affect ventricular repolarization at plasma concentrations up to 200 ng/mL, indicating that HCQ may not increase the risk of QTcF-induced arrhythmias [[126]43]. In our study, within the HCQ combined with PDN group, three patients experienced conduction disorders: two required permanent pacemakers for high-grade atrioventricular block, while one recovered spontaneously. In the PDN monotherapy group, four patients needed pacemakers for high-grade atrioventricular block, and another required an ICD for sustained ventricular tachycardia. We systematically evaluated the safety of and common adverse reactions associated with HCQ treatment. Notably, the incidence of adverse events within 1 year was similar between patients in the HCQ combined with PDN therapy group and those in the PDN monotherapy group, and there were no serious adverse events related to HCQ or PDN treatment, indicating the potential safety of the treatment plan. Although HCQ is a well-known drug in clinical practice, its exact mechanism of action is only beginning to be understood [[127]19]. A cohort study suggested that HCQ might inhibit the IL-1β-GM-CSF axis in the treatment of acute rheumatic fever [[128]44]. In patients with myocardial infarction, the use of HCQ significantly reduced IL-6 compared to placebo [[129]45]. Recent findings from the experimental autoimmune myocarditis mouse model suggest that HCQ could be therapeutically beneficial. By inhibiting the expression of CXCL16 and related pathways, HCQ can improve cardiac function and reduce inflammation, supporting its potential efficacy in chronic infl-CMP [[130]46]. These results suggest that HCQ may exert therapeutic effects on inflammatory diseases by regulating multiple inflammatory factors. In the HYPIC study, we found that HCQ combined with PDN therapy significantly reduced 16 plasma inflammatory proteins to normal levels, whereas PDN monotherapy only reduced 2 of these 16 inflammatory proteins. The results revealed that HCQ might have therapeutic effects on chronic infl-CMP through multiple pathways, including inhibition of lymphocyte chemotaxis, regulation of leukocyte migration, inhibition of cytokine activity, and cytokine-cytokine receptor interactions. The phase II clinical trial has reached its predefined primary clinical endpoint, indicating that sufficient data have been collected to validate our research hypothesis. Given the observation of significant effects and clear trends, we plan to initiate a more rigorous placebo-controlled double-blind multicenter phase III clinical trial to further verify the reliability of the results and eliminate potential biases. Following review and approval from the ethics committee and the data safety monitoring board, it was decided to terminate the current study early. This decision allows us to focus our resources and efforts on designing and conducting the new study, thereby strengthening and expanding the scientific evidence in this field. This study had several limitations. Firstly, the small sample size of 50 patients may limit the statistical power of the analyses and the ability to detect significant differences or effects in individual outcomes. Additionally, the recruitment of all patients from two centers in China contributes to a racial homogeneity that limits the generalizability of our findings to broader, more diverse populations. Such geographic and demographic concentration may impact the global applicability of our results. Secondly, this study was not double-blind, which may introduce bias. Nevertheless, all follow-up doctors, echocardiologists, and blood test doctors were blinded to the clinical characteristics, treatment assignments, and outcomes, and all patients were blinded to the primary and secondary outcomes of the study. A prospective, multicenter, randomized, double-blind, placebo-controlled clinical trial is underway to further demonstrate the effectiveness of HCQ in combination with PDN. Furthermore, the statistical significance of the composite primary endpoint was mainly driven by the reduction in the recurrence of myocarditis, whereas no significant differences between groups were observed for other components of the composite endpoint, which are generally considered more relevant from both clinical and prognostic perspectives. Therefore, the results related to the primary endpoints should be interpreted with caution. Additionally, due to the small sample size and limited number of events, the analysis of individual outcomes may have been underpowered to identify significant differences or effects. Finally, because of the inability to collect plasma from all participants, we only examined plasma inflammatory proteins in 24 patients using the Olink Target 96 inflammation panel. Conclusions In conclusion, in this phase II trial with a limited sample size, HCQ combined with PDN therapy for 12 months reduced the composite cardiovascular outcome of time to cardiovascular death or heart transplant, hospitalization for heart failure, recurrence of myocarditis, permanent pacemaker use, or ICD implantation in patients with chronic infl-CMP after FM. Furthermore, patients in the HCQ combined with PDN therapy group showed more significant improvements in LVEF, LVIDd, hs-cTnI, NT-proBNP, and hs-CRP levels than those in the PDN monotherapy group. HCQ combined with PDN significantly reduced various plasma inflammatory proteins to normal levels. These data suggest that patients with chronic infl-CMP may benefit from the administration of HCQ. Supplementary Information [131]12916_2025_4301_MOESM1_ESM.docx^ (271.4KB, docx) Additional file 1. Trial protocol of the HYPIC trial. [132]12916_2025_4301_MOESM2_ESM.docx^ (844.2KB, docx) Additional file 2: Expanded methods. Tables S1–-S5. Figs. S1–-S3. Table S1. Heart failure medication for the 12th month of follow-up in each group. Table S2. Hospitalization for heart failure and recurrence of myocarditis at 12 months after treatment initiation. Table S3. Recovery of left ventricular ejection fraction over time in each group. Table S4. Impact of prior hospitalization for heart failure on the incidence of composite cardiovascular outcome and recovery of left ventricular ejection fraction at 12 months after treatment initiation. Table S5. Baseline clinical characteristics of patients with chronic inflammatory cardiomyopathy and healthy controls for detecting Olink Target 96 inflammation panel. Fig. S1. Dynamic changes in important clinical indicators. Fig. S2. Differential plasma inflammatory proteins between patients with chronic inflammatory cardiomyopathy and healthy controls via Olink Target 96 inflammation panel. Fig. S3. Restoring normal levels of plasma inflammatory proteins after 12 months of HCQ combined with PDN treatment. [133]Additional file 3. CONSORT checklist.^ (220KB, doc) Acknowledgements