Makindo Medical Notes

🧠 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.