Nelson Textbook of Pediatrics 22nd Edition — CMT1A: PMP22 duplication (17p11.2), autosomal dominant, demyelinating neuropathy. Slow nerve conduction (<38 m/s). Pes cavus, hammer toes, distal muscle atrophy (stork leg), areflexia, palpably enlarged nerves. HNPP (PMP22 deletion) causes episodic pressure palsies.
🌐 paeds.online — Pakistan's Pediatric Platform| Feature | CMT1A (PMP22 duplication) | HNPP (PMP22 deletion) |
|---|---|---|
| Inheritance | Autosomal dominant | Autosomal dominant |
| Gene defect | Duplication 17p11.2 (PMP22) | Deletion 17p11.2 (PMP22) |
| Nerve conduction | Slow (<38 m/s, demyelinating) | Mild slowing, focal conduction block |
| Clinical presentation | Progressive distal weakness, pes cavus, hammer toes, areflexia, onset childhood/adolescence | Episodic pressure palsies (carpal tunnel, peroneal palsy), tomaculous myelin |
| Sural nerve biopsy | Onion bulb formations | Tomaculous (sausage-shaped) myelin thickenings |
| Pathology | Hypertrophic demyelinating neuropathy | Focal myelin overgrowth, liability to pressure |
CMT1A (PMP22 duplication): Most common CMT (>70%). Onset late childhood to adolescence. Distal muscle atrophy (peroneal → stork leg), pes cavus, hammer toes, areflexia, palpably enlarged nerves (ulnar, greater auricular). Sensory loss (vibration, proprioception). Slowly progressive; normal lifespan.
Nerve conduction studies: Motor nerve conduction velocity <38 m/s (demyelinating). Prolonged distal latencies, reduced amplitudes.
Genetic testing: PMP22 duplication (FISH, MLPA) — first-line test.
HNPP (PMP22 deletion): Presents with recurrent mononeuropathies (wrist drop, foot drop) after minor compression. Sural nerve biopsy: tomaculous (sausage-shaped) myelin.