A 52-year-old man from Delhi presents with recurrent episodes of acute pancreatitis over the past 6 months. He denies alcohol use. Physical examination reveals eruptive xanthomas over his elbows and knees. Fasting lipid panel shows: Total cholesterol 680 mg/dL, Triglycerides 1200 mg/dL, HDL 28 mg/dL, LDL 120 mg/dL. Serum amylase is elevated. Abdominal ultrasound shows no gallstones. What is the most likely lipoprotein abnormality responsible for his presentation?

Explanation

## Clinical Presentation Analysis **Key Point:** The combination of severe hypertriglyceridemia (>1000 mg/dL), eruptive xanthomas, and recurrent acute pancreatitis in the absence of secondary causes (no alcohol, no gallstones) is pathognomonic for **Type I Hyperlipoproteinemia** (familial chylomicronemia syndrome). ## Pathophysiology **High-Yield:** Type I hyperlipoproteinemia results from deficiency of: - **Lipoprotein lipase (LPL)** — the enzyme responsible for hydrolysis of triglycerides in chylomicrons and VLDL, OR - **ApoC-II** — a cofactor required for LPL activation Without functional LPL or its cofactor, chylomicrons accumulate in the bloodstream, causing: 1. Severe hypertriglyceridemia (often >1000 mg/dL) 2. Eruptive xanthomas (lipid deposition in skin) 3. Lipemic plasma (milky appearance) 4. Recurrent acute pancreatitis (triglycerides >500 mg/dL increase risk) ## Laboratory Findings in Type I | Feature | Type I | Type II | Type III | Type IV | |---------|--------|---------|----------|----------| | **Chylomicrons** | ↑↑↑ Marked | Normal | Normal | Normal | | **Triglycerides** | >1000 mg/dL | Normal | ↑ Moderate | ↑ Moderate | | **Total Cholesterol** | ↑↑ | ↑↑↑ | ↑↑ | Normal/↑ | | **LDL** | Normal/Low | ↑↑↑ | ↑ | Normal | | **Eruptive Xanthomas** | Yes | No | No | No | | **Pancreatitis Risk** | Very High | Low | Low | Moderate | **Clinical Pearl:** The normal LDL (120 mg/dL) in this patient is a key discriminator — it rules out Type II (familial hypercholesterolemia), where LDL would be markedly elevated. ## Diagnostic Confirmation **Mnemonic:** **CHYLO** = Chylomicronemia, Hypertriglyceridemia, Lipase deficiency (or apoC-II), Opalescent plasma, Pancreatitis - Lipemic (milky) plasma on visual inspection - Lipoprotein electrophoresis shows prominent chylomicron band - Apolipoprotein C-II level can be measured to differentiate LPL vs. apoC-II deficiency - Post-heparin lipolytic activity is reduced or absent ## Management Implications - **Strict dietary fat restriction** (<20 g/day) - **Medium-chain triglyceride (MCT) supplementation** (bypasses chylomicron pathway) - **Fibrates and statins** have limited benefit - **Genetic counseling** — autosomal recessive inheritance [cite:Harrison 21e Ch 406]