Makindo Medical Notes

🧠 Length Dependent Polyneuropathy (LDPN) is the most common form of polyneuropathy. The longest axons — sometimes reaching up to 1 metre — are the most vulnerable to damage, hence the “length dependent” pattern.

About

• LDPN typically begins in the feet and ascends gradually (“stocking-glove” distribution).
• The longest axons are most affected, leading to distal > proximal weakness and sensory loss.

Aetiology

• 🔹 The sensory axon cell body lies in the dorsal root ganglion.
• 🔹 The motor axon cell body originates from the anterior horn cell of the spinal cord.
• Motor-predominant LDPN → more likely genetic.
• Sensory-predominant LDPN → usually toxic or metabolic.

Common Causes

• 🧬 Genetic: Charcot-Marie-Tooth Disease, Hereditary Sensory Neuropathy.
• 🩸 Metabolic: Diabetes mellitus* (the most common), prediabetes, Uraemia.
• 🥦 Nutritional Deficiencies: Vitamin B12, B1 deficiency, B6 toxicity.
• 🛡️ Autoimmune: Sjögren’s syndrome, Rheumatoid arthritis, Sarcoidosis.
• 🦠 Infections: HIV (esp. with low CD4), Lyme disease.
• 🍷☠️ Toxic: Alcohol abuse*, heavy metals (Arsenic, Lead, Mercury, Thallium), Organophosphates.
• 💊 Drugs: Amiodarone, Colchicine, Isoniazid, Hydralazine, Metronidazole, Thalidomide, Vincristine.
• 🎗️ Paraneoplastic: Small cell lung cancer with Anti-Hu antibodies.
• ⚠️ Others: MGUS, Amyloidosis, Coeliac disease, Hypothyroidism, Critical illness polyneuropathy.

Clinical Features

• 👣 Sensory loss: painful feet, “walking on cotton wool” sensation.
• 🌙 Sensory ataxia: imbalance worse at night due to loss of proprioception.
• 💪 Distal weakness: especially toe extensors and foot everters.
• ⬇️ Reduced ankle reflexes (ankle jerks).
• ✋ When sensory loss reaches mid-shin → hands become involved (“glove” pattern).
• 🦶 Pes cavus (high-arched feet), particularly in Charcot-Marie-Tooth type 1.

Investigations

• 🔍 See Peripheral Neuropathy section for full workup (blood tests, neurophysiology, genetic testing where indicated).

Management

• 🛠️ As per Peripheral Neuropathy principles: treat underlying cause, provide symptomatic relief (e.g. neuropathic pain agents), and consider physiotherapy/orthotics.