## Organ Involvement in Visceral Leishmaniasis **Key Point:** The **spleen** is the most commonly and most severely affected organ in kala-azar, often reaching massive proportions (up to 8–10 times normal size). ### Pattern of Organ Involvement in Kala-azar | Organ | Frequency | Severity | Clinical Significance | |-------|-----------|----------|----------------------| | **Spleen** | ~100% | Massive (often 8–10× normal) | Splenic rupture possible; major source of parasites | | **Liver** | ~90% | Moderate hepatomegaly | Hepatic dysfunction, cirrhosis in chronic cases | | **Bone marrow** | ~85% | Parasites in macrophages | Pancytopenia, diagnostic site | | **Lymph nodes** | ~75% | Regional/generalized | Lymphadenopathy variable | | **Kidneys** | ~50% | Glomerulonephritis | Immune complex deposition | | **GI tract** | Variable | Mucosal infiltration | Diarrhea, protein loss | **High-Yield:** The spleen in kala-azar is characteristically: - **Massive** (often palpable below the iliac crest) - **Firm** and **non-tender** - **Teeming with amastigotes** within macrophages - A major source of parasites for transmission to sand flies ### Pathophysiology of Splenic Enlargement 1. **Parasitized macrophage infiltration** — *L. donovani* amastigotes proliferate within splenic macrophages 2. **Hyperplasia of reticuloendothelial system** — reactive proliferation of macrophages and lymphocytes 3. **Immune activation** — polyclonal B-cell activation and hypergammaglobulinemia 4. **Portal hypertension** — splenic enlargement may lead to portal congestion (rare) **Clinical Pearl:** Splenic rupture, though rare, is a life-threatening complication that can occur spontaneously or after trauma. The spleen should be protected during examination. **Mnemonic:** **SPLEEN** — **S**plenic enlargement **P**redominates, **L**arge organ **E**ven **E**arly, **N**ormally firm. [cite:Harrison 21e Ch 297]
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