A 58-year-old man from Mumbai presents with progressive dyspnea on exertion and orthopnea for 6 months. On examination, he has a blood pressure of 145/92 mmHg, JVP elevation, and bilateral ankle edema. Echocardiography shows a thickened, restrictive left ventricle with ejection fraction of 45% and a characteristic 'granular sparkling' appearance of the myocardium. Serum creatinine is 1.8 mg/dL and urinalysis shows proteinuria (2.5 g/24 h). A cardiac biopsy stained with Congo red under polarized light shows apple-green birefringence. Which type of amyloidosis is most likely responsible for this clinical presentation?

Explanation

## Diagnosis: AL Amyloidosis ### Clinical Presentation Analysis **Key Point:** The combination of restrictive cardiomyopathy with renal involvement (proteinuria, elevated creatinine) and the characteristic echocardiographic findings strongly suggest AL amyloidosis. ### Distinguishing Features of AL Amyloidosis | Feature | AL Amyloidosis | AA Amyloidosis | ATTRwt | Aβ2M | |---------|---|---|---|---| | **Primary organ involvement** | Heart, kidneys, nerves | Kidneys, GI tract, liver | Heart, nerves, carpal tunnel | Bone, joints, carpal tunnel | | **Renal involvement** | Nephrotic syndrome common | Nephrotic syndrome (most common) | Rare | Rare | | **Cardiac involvement** | Restrictive cardiomyopathy (common) | Uncommon | Common in elderly males | Rare | | **Age of onset** | 50–70 years | Any age (chronic inflammation) | >60 years | >50 years (dialysis) | | **Etiology** | Plasma cell dyscrasia (misfolded light chains) | Chronic inflammation (TB, RA, chronic infection) | Mutant TTR gene or wild-type TTR | Accumulation in dialysis patients | | **Gender predominance** | M:F ~2:1 | Equal | Male predominance | Equal | **High-Yield:** AL amyloidosis accounts for ~70% of all amyloidosis cases and is the most common form seen in developed countries. The dual involvement of heart and kidney in a middle-aged patient is pathognomonic for AL. ### Pathophysiology of AL Amyloidosis 1. **Clonal plasma cell disorder** produces misfolded immunoglobulin light chains (κ or λ). 2. **Misfolded light chains** aggregate into β-pleated sheet structures → amyloid fibrils. 3. **Organ deposition** → restrictive cardiomyopathy (most common cardiac presentation), nephrotic syndrome, autonomic neuropathy, hepatomegaly. 4. **Congo red staining** with **apple-green birefringence under polarized light** is the gold standard diagnostic finding. **Clinical Pearl:** AL amyloidosis patients often present with "restrictive" physiology on echo (thickened walls, reduced cavity size, restrictive filling pattern) — this mimics constrictive pericarditis but is due to amyloid infiltration of the myocardium itself. ### Why This Patient Has AL, Not Other Forms - **Cardiac involvement + renal involvement** → AL (AA typically spares the heart; ATTRwt spares the kidneys; Aβ2M spares both). - **Age 58, no chronic inflammatory disease history** → rules out AA (which requires chronic inflammation like TB, RA). - **No dialysis history** → rules out Aβ2M. - **No family history mentioned, male, age <70** → less likely ATTRwt (which is typically >60, often with family history or neuropathy). ### Diagnostic Confirmation **Mnemonic: CRAB** (Congo red, Restriction physiology, AL type, Biopsy confirms): - **Congo red staining** of tissue biopsy with **apple-green birefringence** under polarized light = diagnostic. - **Immunohistochemistry** or **mass spectrometry** of biopsy to identify light chain type (κ or λ). - **Serum/urine free light chain assay** — elevated ratio (κ/λ or λ/κ). - **Bone marrow biopsy** — may show clonal plasma cells (10–30% of AL cases have concurrent multiple myeloma). **High-Yield:** AL amyloidosis is a medical emergency if cardiac involvement is present; median survival without treatment is ~1 year for cardiac AL.