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CMT Type I

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- Discussion:
    - autosomal dominant inheritance;
    - type-I and III disorders are due to demyelination of peripheral nerves;
    - clinical presentation is most common during the second decade of life;
    - due to defect in the gene coding for peripheral myelin protein-22 on chromosome 17;
    - EMG in demyelinating neuropathies:
           - motor nerve-conduction study reveals marked slowing of rate of impulse conduction;
    - biopsy:
           - biopsy of a distal muscle such as the gastrocnemius demonstrates a neuropathic pattern;
           - in pts for whom diagnosis remains unclear, categorization is aided by biopsy of the sural nerve, which demonstrates demyelination;

- Clinical Manifestations:
    - symptoms do not manifest until adolescence;
    - patients note weakness in the legs followed by weakness in the intrinsics of the hand;
    - ataxia
    - generalized tendon areflexia
    - distal sensory loss (esp light touch, position, and vibration sense);
    - hands:
           - weakness in hands, upper limb tremor;
    - foot:
           - mild cavus deformity or clawing of toes may be first clinical manifestation;
           - abnormal foot position is initially flexible, but with increasing peroneal involvement, an equinovarus deformity gradually develops;
           - pt experiences pain under the lateral metatarsal heads during wt bearing and has difficulty in running;
           - look for lateral wear on soles of shoes

The gene for the peripheral myelin protein PMP-22 is a candidate for Charcot-Marie-Tooth disease type 1A.