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Charcot-Marie-Tooth disease type 1 (CMT1, hereditary sensorimotor polyneuropathy type-1, HSMN1)
Demyelinating polyneuropathy.
Epidemiology:
- most common hereditary neuropathy [1]
Pathology:
1) abnormal myelin formation
2) Schwann cell proliferation
Genetics:
1) autosomal dominant
2) most kindreds have a duplication at 17p11.2
Clinical manifestations: (also see Charcot-Marie-Tooth disease)
1) slowly progressive distal muscle atrophy & weakness
2) absent deep tendon reflexes
3) high arched feet & palate may be present
4) hammer toes
5) palpably enlarged peripheral nerves
Laboratory:
- CMT1 gene mutation [1]
Special laboratory:
1) nerve conduction studies:
a) decreased nerve conduction velocity characteristic of demyelinating neuropathy (50% of normal conduction velocity) (< 38 m/s)
b) diagnostic test of choice
c) few other disorders show this degree of nerve conduction velocity slowing
2) electromyography:
a) enlarged motor unit potential
b) reduced recruitment
c) fibrillation potentials not prominent
3) muscle biopsy shows chronic denervation, a non-specific finding
Specific
Charcot-Marie-Tooth disease type 1A; hereditary motor & sensory neuropathy 1A (CMT1A)
Charcot-Marie-Tooth disease type 1B (CMT1B)
Charcot-Marie-Tooth disease type 1C (CMT1C)
Charcot-Marie-Tooth disease type 1D (CMT1D)
Charcot-Marie-Tooth disease type 1E (CMT1E)
Charcot-Marie-Tooth disease type 1F (CMT1F)
Charcot-Marie-Tooth disease type 1X (CMTX)
General
Charcot-Marie-Tooth disease (peroneal muscle atrophy, hereditary sensorimotor polyneuropathy (HSMN))
References
- Medical Knowledge Self Assessment Program (MKSAP) 11, 17, 18.
American College of Physicians, Philadelphia 1998, 2015, 2018