Case report reveals systemic light chain amyloidosis in a patient with myopathy and proteinuria, highlighting the risk of misdiagnosis as inflammatory disease.
Key Points
To describe the clinical presentation, diagnostic evaluation, and therapeutic response of systemic light chain amyloidosis initially misdiagnosed as idiopathic inflammatory myopathy.
Clinical, biochemical, and echocardiographic evaluation of a 58-year-old male presenting with progressive proximal muscle weakness, peripheral oedema, and weight loss after failing immunosuppressive therapy.
Renal tissue biopsy assessed via light microscopy, Congo red staining under polarized light, immunofluorescence, and transmission electron microscopy.
Bone marrow examination and treatment with 13 cycles of bortezomib, cyclophosphamide, and dexamethasone (VCD) with serial biomarker and echocardiographic follow-up.
Kidney biopsy confirmed amyloidosis with Congo red-positive apple-green birefringence and non-branching 11 nm fibrils, while serum free light chain (FLC) testing revealed an elevated λ-FLC level of 470 mg/L and an abnormal κ:λ ratio of 0.035.
Echocardiography demonstrated severe biventricular wall thickening with apical contractility preservation ('cherry-on-top' pattern), accompanied by elevated cardiac troponin I (139 ng/L) and B-type natriuretic peptide (2112 ng/L).
VCD chemotherapy normalized the κ:λ FLC ratio at 3 months, improved serum albumin from 24 g/L to 30 g/L, and reduced the urine protein–creatinine ratio from 0.37 g/mmol to 0.07 g/mmol, though ventricular hypertrophy and heart failure symptoms persisted.