Neurology · MU Sofia

74. Hereditary motor and sensory polyneuropathy

Explains hereditary motor and sensory polyneuropathy as a genetic, slowly progressive distal nerve disorder, with Charcot–Marie–Tooth disease as its most common form. Covers inheritance patterns and the demyelinating versus axonal types, then the clinical signs such as foot drop, distal wasting, steppage gait and deformities, shown in a picture. Also outlines nerve conduction and genetic diagnosis, differential diagnoses, supportive treatment and prognosis.

Inside: 1 section · 1 labelled picture · 15 flashcards · 2 min

Topic 74 of 88 in the MU Sofia syllabus for Neurology (Medicine, Year 4). The free AceMed note covers it in 1 section, about 322 words (2 min of reading), with 15 flashcards.

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  1. Hereditary motor and sensory polyneuropathy

Hereditary motor and sensory polyneuropathy

Definition: Hereditary motor and sensory polyneuropathy (HMSN) is a group of genetic peripheral nerve disorders characterized by progressive degeneration of peripheral nerves, leading to both motor and sensory deficits, usually in a length-dependent pattern.

→ Most common form: Charcot–Marie–Tooth disease (CMT).

Etiology & Genetics

  • Main Inheritance Patterns: Autosomal dominant (most common). Autosomal recessive. X-linked forms
  • Genetic defect
  • Mutations affecting: Myelin proteins (demyelinating forms). Axonal transport (axonal forms)

Pathogenesis

Two main pathological types:

  1. A. Demyelinating Type (CMT1) : Primary myelin sheath damage. ↓ nerve conduction velocity
  2. B. Axonal Type (CMT2): Axon degeneration. Normal or mildly reduced conduction velocity

→ Result: distal nerve degeneration (“dying-back neuropathy”)

Clinical Features

  1. 1. Motor Symptoms: Progressive distal muscle weakness. Foot drop (early sign). Difficulty walking. Weak hand grip (late)
  2. 2. Muscle Atrophy: “Inverted champagne bottle legs”. Thin distal legs. Relatively preserved proximal muscles
  3. 3. Sensory Symptoms: Loss of vibration and proprioception. Numbness and tingling (distal). Reduced pain/temperature (variable)
  4. 4. Reflexes: Hyporeflexia or areflexia (ankle reflex lost early)
  5. 5. Deformities: Pes cavus (high arched foot). Hammer toes. Scoliosis (sometimes)

Examination Findings: Distal muscle wasting (legs > arms). Foot drop with steppage gait. Reduced ankle reflexes. Sensory loss in stocking distribution. Pes cavus deformity

Gait Pattern: Steppage gait (lifting feet high to avoid dragging toes)

Diagnosis

Clinical Diagnosis (key): Slowly progressive distal motor + sensory neuropathy. Family history often present

Nerve Conduction Studies

  • Demyelinating type: slow conduction velocity
  • Axonal type: reduced amplitude

EMG: Neurogenic pattern of denervation

Genetic Testing: Confirms subtype (PMP22 duplication common in CMT1A)

Differential Diagnosis

  1. 1. Acquired Polyneuropathy (e.g., diabetes): Later onset. No strong family history
  2. 2. Spinal Muscular Atrophy: Pure motor (no sensory loss)
  3. 3. Myopathies: Proximal weakness (not distal). Normal sensation
  4. 4. Multiple Sclerosis: CNS signs (UMN, not peripheral)

Treatment

  • No curative therapy
  • Supportive Treatment: Physiotherapy. Orthotic devices (foot braces). Occupational therapy. Pain management if needed
  • Surgical: Correction of foot deformities (severe cases)

Prognosis: Slowly progressive. Life expectancy usually normal. Variable disability depending on subtype

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