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?

Question

Accepted Answer

B. Endomyocardial biopsy with Congo red staining and immunofluorescence. ## 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]

Answer

A. Technetium-99m pyrophosphate cardiac scintigraphy

Answer

C. Start diuretics and ACE inhibitors; repeat echocardiography in 3 months

Answer

D. Serum and urine protein electrophoresis followed by bone marrow biopsy

Explanation

Diagnostic Strategy in Suspected Cardiac Amyloidosis

Clinical Presentation Clues

Diagnostic Algorithm

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