Hydroxychloroquine serves as a cornerstone disease-modifying antirheumatic drug for managing rheumatoid arthritis, systemic lupus erythematosus, and diverse dermatological disorders across clinical practice. Although healthcare providers generally consider the medication safe, long-term administration carries a recognized risk of severe adverse effects, notably cardiotoxicity. Clinicians frequently encounter diagnostic dilemmas when distinguishing drug-induced myocardial damage from primary infiltrative cardiomyopathies. In particular, HCQ cardiomyopathy can mimic the clinical, structural, and echocardiographic characteristics of transthyretin cardiac amyloidosis. Scintigraphy using technetium-99m pyrophosphate, commonly termed a PYP scan, represents the established noninvasive standard for diagnosing transthyretin cardiac amyloidosis. However, profound drug-induced storage alterations can produce false positive results on bone scintigraphy scans. Consequently, relying exclusively on noninvasive nuclear imaging without assessing pretest clinical probability creates significant diagnostic confusion. Clinicians must integrate thorough pharmacological histories, multimodal imaging, and histopathological analysis to achieve diagnostic clarity.

Clinical Presentation of HCQ Cardiomyopathy and Amyloidosis Overlap

Patients who develop cardiotoxicity from chronic hydroxychloroquine exposure frequently present with insidious symptoms that mirror common cardiac conditions. For instance, typical clinical manifestations include progressive exertional dyspnea, peripheral edema, lightheadedness, pre-syncope, and profound conduction system disease. Advanced atrioventricular block, bundle branch blocks, and recurrent ventricular arrhythmias frequently develop as myocardial injury progresses over time. In addition, transthoracic echocardiography typically reveals symmetric concentric biventricular hypertrophy, reduced left ventricular ejection fraction, biatrial enlargement, and restrictive diastolic dysfunction. Because these echocardiographic features closely parallel the classic appearance of infiltrative disorders like cardiac amyloidosis, clinicians routinely request noninvasive nuclear imaging to confirm their diagnostic suspicions. Furthermore, prolonged cumulative drug exposure spanning decades substantially increases the likelihood of severe myocyte damage. Therefore, when evaluating autoimmune disease patients presenting with unexplained heart failure, clinicians must maintain a high index of suspicion for drug toxicity rather than assuming a primary amyloid etiology. Integrating careful pharmacological reviews into routine cardiac evaluations remains essential for identifying these complex clinical presentations early.

Mechanisms Underlying False Positive PYP Scintigraphy

Technetium-99m pyrophosphate scintigraphy demonstrates exceptional specificity and sensitivity for transthyretin cardiac amyloidosis when clinicians exclude monoclonal gammopathies. Under typical conditions, planar and SPECT imaging show intense myocardial radiotracer retention corresponding to visual grade 2 or 3 uptake and high heart-to-contralateral lung ratios. However, hydroxychloroquine accumulates heavily in acidic lysosomes and raises intracellular pH, thereby inhibiting essential lysosomal enzymes such as alpha-galactosidase. As a result, incomplete metabolic degradation causes massive cytoplasmic accumulation of phospholipids, autophagic vacuoles, and cellular debris within cardiomyocytes. Consequently, advanced cellular degeneration, disrupted sarcolemmal integrity, and altered intracellular calcium homeostasis promote non-specific radiotracer binding within the myocardium. Thus, extensive drug-induced vacuolar myopathy can produce marked tracer retention that mimics amyloid fibrils on bone scintigraphy. Recognizing these unusual non-amyloid causes of positive scans is vital because misinterpretation can lead to inappropriate therapies. Therefore, clinicians must carefully interpret scintigraphic results within the broader context of medication history and pretest clinical probability.

Pathological Hallmarks and the Value of Endomyocardial Biopsy

Because noninvasive imaging cannot definitively separate severe drug-induced storage myopathy from infiltrative amyloidosis in discordant scenarios, invasive tissue sampling remains essential. Specifically, endomyocardial biopsy provides definitive histopathological evidence that resolves diagnostic dilemmas. Under light microscopy, tissue sections from affected patients demonstrate diffuse cytoplasmic vacuolization of cardiomyocytes without extracellular amyloid deposition. Moreover, Congo red staining with polarized light microscopy remains consistently negative, effectively ruling out light-chain and transthyretin amyloidosis. In addition, transmission electron microscopy serves as the gold standard for confirmation by revealing characteristic ultrastructural alterations. These include numerous pleomorphic myeloid bodies, lamellar myelin figures, and curvilinear bodies within secondary lysosomes. Importantly, these specific ultrastructural findings differentiate antimalarial cardiotoxicity from genetic lysosomal disorders such as Fabry disease. Consequently, obtaining a tissue diagnosis prevents the inappropriate initiation of expensive amyloid-targeted therapeutics. Furthermore, early histological confirmation guides the immediate cessation of the toxic agent, offering patients the best opportunity for clinical stabilization.

Therapeutic Management and Clinical Reversibility

The primary therapeutic intervention for hydroxychloroquine-induced cardiotoxicity involves the immediate and permanent cessation of the culprit medication. However, because hydroxychloroquine possesses an extensive volume of distribution and a prolonged terminal elimination half-life exceeding forty days, clinical recovery often requires several months. Therefore, multidisciplinary collaboration between cardiologists and rheumatologists is essential to select alternative, non-cardiotoxic immunosuppressive agents to manage underlying autoimmune diseases effectively. Simultaneously, clinicians must institute guideline-directed medical therapy for heart failure, including beta-blockers, mineralocorticoid receptor antagonists, and sodium-glucose cotransporter-2 inhibitors as clinically tolerated. In addition, patients experiencing high-grade conduction abnormalities or life-threatening ventricular arrhythmias require urgent device therapy, such as permanent pacemakers or cardiac resynchronization therapy defibrillators. Furthermore, regular clinical monitoring using serial echocardiography, serum cardiac biomarkers, and ambulatory electrocardiography is crucial to track myocardial recovery. Although some structural damage may persist, prompt drug withdrawal frequently halts disease progression and prevents further cardiac deterioration.

Risk Stratification and Screening Protocols in Chronic Therapy

Preventing advanced cardiotoxicity requires proactive risk assessment and structured monitoring protocols for all patients undergoing long-term antimalarial therapy. Clinicians should routinely calculate cumulative lifetime doses, as total exposure exceeding several hundred grams significantly elevates the risk of cardiac and retinal toxicity. Furthermore, baseline electrocardiograms and periodic surveillance can detect early conduction abnormalities, such as PR interval prolongation, bundle branch blocks, or QTc prolongation, before overt heart failure develops. In addition, clinicians must maintain heightened vigilance when treating elderly patients or individuals with pre-existing renal insufficiency, as impaired drug clearance accelerates systemic accumulation. When patients on long-term therapy report unexplained dyspnea, fatigue, or palpitations, clinicians should promptly order serum biomarkers and echocardiography. Accordingly, early detection of subclinical cardiac dysfunction allows for timely dosage adjustment or medication substitution. Implementing these proactive surveillance strategies safeguards patients against preventable, irreversible myocardial injury while ensuring effective disease control.

Frequently Asked Questions

How does hydroxychloroquine cause false positive findings on a PYP scan?

Hydroxychloroquine inhibits lysosomal enzymes, leading to intracellular accumulation of autophagic vacuoles and complex lipids within cardiomyocytes. Consequently, advanced cellular degeneration and disrupted calcium homeostasis promote non-specific binding of technetium-99m pyrophosphate to damaged myocardial tissue. Therefore, the scan exhibits diffuse radiotracer retention that mimics the characteristic pattern of transthyretin cardiac amyloidosis, resulting in a false positive interpretation despite the total absence of amyloid fibrils.

What are the definitive pathological features of HCQ cardiomyopathy?

Definitive diagnosis requires endomyocardial biopsy evaluated with light and electron microscopy. Light microscopy reveals enlarged cardiomyocytes with marked cytoplasmic vacuolization and negative Congo red staining. Furthermore, transmission electron microscopy demonstrates pathognomonic ultrastructural hallmarks, specifically lamellar myelin figures, pleomorphic myeloid bodies, and curvilinear bodies within secondary lysosomes. These distinctive electron microscopic findings definitively confirm drug-induced lysosomal storage dysfunction while excluding other storage diseases.

Is hydroxychloroquine cardiotoxicity reversible after stopping the drug?

Myocardial recovery depends heavily on the extent of tissue damage present before drug cessation. Because hydroxychloroquine has a prolonged elimination half-life, clinical stabilization and structural remodeling may require several months. While early discontinuation frequently halts functional decline and improves symptoms, advanced fibrosis and extensive conduction system disease may remain irreversible, necessitating permanent device therapy alongside optimized medical heart failure management.

Disclaimer: This content is for informational and educational purposes only and does not constitute medical advice. Healthcare professionals should evaluate clinical decisions independently. Refer to the latest local and national guidelines for clinical practice.

References

1. Florencio Dos Santos LW et al. Hydroxychloroquine-Induced Cardiotoxicity in the Setting of a False Positive PYP Scan. JACC Case Rep. 2026 Aug 29. doi: undefined. PMID: 42667285.


2. Chang ICY, Bois JP, Bois MC, et al. Hydroxychloroquine-mediated cardiotoxicity with a false-positive 99m technetium-labeled pyrophosphate scan for transthyretin-related cardiac amyloidosis. Circ Cardiovasc Imaging. 2018;11(1):e007059.


3. Layoun ME, Desmarais J, Heitner SB, et al. Hot hearts on bone scintigraphy are not all amyloidosis: hydroxychloroquine-induced restrictive cardiomyopathy. Eur Heart J. 2020;41(25):2414.