Hereditary neuropathy with pressure palsies
Hereditary Neuropathy with Pressure Palsies (HNPP) Overview
🧠 Hereditary Neuropathy with Pressure Palsies (HNPP) is a rare genetic neuropathy that causes recurrent, focal episodes of numbness and weakness after only mild nerve compression. It is important to distinguish from common acquired neuropathies like diabetes or vasculitis.
📖 About
- HNPP is an autosomal dominant disorder causing multiple episodes of focal mononeuropathy.
- Often triggered by seemingly trivial pressure (e.g., leaning on an elbow, crossing legs, or carrying a bag strap).
- Most patients recover function, but recurrence is common.
🧬 Aetiology
- Caused by mutations or deletions in the PMP22 gene, critical for myelin production.
- A single abnormal gene copy is sufficient → autosomal dominant inheritance.
🔬 Pathology
- Patchy demyelination and slowed conduction along nerves.
- Tomacula: “sausage-shaped” thickened myelin segments seen on nerve biopsy — a classic diagnostic clue.
- Changes may even appear in asymptomatic carriers.
🩺 Clinical Features
- Recurrent focal numbness, tingling, or weakness after mild compression or minor trauma.
- Episodes usually last days to weeks; recovery can be incomplete or prolonged.
- Common sites: Median nerve (carpal tunnel), ulnar nerve (elbow), peroneal nerve (fibular head).
- Onset usually in adolescence or young adulthood (2nd–3rd decade).
- Males sometimes present with more severe disease.
🧪 Investigations
- Nerve Conduction Studies (NCS): Show patchy demyelination, conduction block, and slowing at compression-prone sites.
- Genetic Testing: PMP22 deletion/duplication testing confirms the diagnosis.
🧾 Differential Diagnosis
- Diabetic Neuropathy: More symmetric, length-dependent polyneuropathy.
- Vasculitic Neuropathy: Mononeuritis multiplex but usually with systemic features (rash, fever, raised ESR/CRP).
⚕️ Management
- Avoidance of Triggers:
- Don’t cross legs or lean on elbows for prolonged periods.
- Avoid kneeling, repetitive wrist movements, or using tight straps/tools.
- Lifestyle: Maintain healthy weight to reduce nerve compression risk.
- Supportive Care: Physiotherapy and occupational therapy for residual weakness.
- Genetic Counselling: Essential for affected families planning children.
- Recovery is variable — some patients improve fully, others are left with mild deficits.
📚 References
- Lai SP, Gorson M. Hereditary neuropathy with pressure palsies. NEJM. 2002;347:1946–53.
- Vallat JM, Boespflug-Tanguy O. HNPP: genetic & clinical features. JNNP. 2001;71:297–303.
- van der Zwaag B, Houlden H. HNPP overview. Curr Opin Neurol. 2006;19:283–8.
