A 58-year-old man from Mumbai presents with progressive dyspnea, orthopnea, and lower limb edema for 3 months. Echocardiography shows restrictive cardiomyopathy with biatrial enlargement and normal ejection fraction. Serum creatinine is 1.8 mg/dL with proteinuria (2.5 g/24 h). Cardiac MRI shows late gadolinium enhancement in a subendocardial pattern. Suspecting cardiac amyloidosis, what is the most appropriate next step in management?

Explanation

## Diagnostic Strategy in Suspected Cardiac Amyloidosis **Key Point:** Endomyocardial biopsy with Congo red staining and immunofluorescence is the gold standard for definitive diagnosis of cardiac amyloidosis and determination of amyloid type (AL vs. ATTR). ### Clinical Presentation Clues - Restrictive cardiomyopathy pattern (normal EF, biatrial enlargement, diastolic dysfunction) - Concurrent renal involvement (elevated creatinine, proteinuria) → suggests systemic amyloidosis - Subendocardial late gadolinium enhancement on cardiac MRI → highly suggestive of amyloid infiltration ### Diagnostic Algorithm ```mermaid flowchart TD A[Suspected cardiac amyloidosis]:::outcome --> B{Clinical + imaging findings consistent?}:::decision B -->|Yes| C[Endomyocardial biopsy with Congo red staining]:::action C --> D{Amyloid confirmed?}:::decision D -->|Yes| E[Immunofluorescence or mass spectrometry]:::action E --> F{AL vs. ATTR?}:::decision F -->|AL| G[Serum/urine protein electrophoresis, bone marrow biopsy]:::action F -->|ATTR| H[Genetic testing if hereditary suspected]:::action G --> I[Chemotherapy if AL-amyloidosis]:::action H --> J[Tafamidis or supportive care]:::action ``` **High-Yield:** Endomyocardial biopsy is essential because: 1. Confirms amyloid deposition histologically (Congo red + apple-green birefringence under polarized light) 2. Determines amyloid type via immunofluorescence (anti-λ, anti-κ for AL; anti-transthyretin for ATTR) 3. Guides specific therapy (chemotherapy for AL; tafamidis for ATTR) **Clinical Pearl:** The combination of restrictive cardiomyopathy + renal dysfunction + subendocardial LGE is pathognomonic for systemic amyloidosis and mandates tissue diagnosis before initiating type-specific therapy. **Warning:** ~~Serum/urine protein electrophoresis alone cannot diagnose cardiac amyloidosis~~ — it screens for monoclonal proteins in AL-amyloidosis but does not prove cardiac infiltration. Tissue diagnosis is mandatory. [cite:Robbins 10e Ch 6]