Makindo Medical Notes.com

Age of onset is variable according to subtype, penetrance,familial phenotype, and ascertainment bias

About

• Length dependent peripheral sensory and motor neuropathy
• Also called Hereditary sensorimotor neuropathy (HSMN Type 1)
• Motor loss tends to predominate rather than sensory
• Sensory loss may be subclinical

Epidemiology

• Prevalence: 40 per 100,000 ( 1 in 2500)
• Males>Females
• Less common in African Americans

Aetiology

• Most are inherited as AD others AR and XLR
• Most forms are myelin based though some have axonal degeneration
• The gene on Chromosome 17 encodes a myelin protein PMP22
• More than 50 genes causing CMT have been identified

Associations

• Retinitis pigmentosia (CMT7)

Image: The foot of a person with Charcot-Marie-Tooth disease: The lack of muscle, a high arch, and claw toes are signs of this genetic disease.

Clinical

• Glove and stocking losses and distal muscle wasting
• Claw hands, cramps, sensory symptoms may come on later
• Hypertrophy of the proximal muscles - inverted champagne bottle
• May be palpable nerve thickening - ulnar and common peroneal
• Comes on age 10-30 with pes cavus (high arched feet)
• Some may have flat feet (Pes plannus)
• Distal muscle wasting of legs appear as "inverted champagne bottles"
• Foot drop and distal "stocking" sensory loss and absent ankle jerks
• Recall being bad at sports and difficulty running and a similar family history

Different forms

Investigations

• DNA analysis helpful for some forms of CMT
• Nerve conduction studies - see above most commonly slowed conduction
• Electromyography
• Lumbar puncture and CSF analysis - elevated protein with Type III

Worsened by

• Emotional stress
• Periods of prolonged immobility
• Pregnancy, Drugs
• Vincristine, amiodarone, Colchicine etc.

Management

• Life expectancy: normal. Some have sleep apnoea
• Pregnancy Disease exacerbation can occur in pregnancy, an effect that may be mediated by increased plasma progesterone
• Genetic counselling that disease may affect offspring
• Counsel that symptoms can worsen with pregnancy
• Good foot care and avoidance of walking barefoot and inspecting feet for injuries that are not felt.
• In severe cases wheelchair may be needed for mobilisation

References

• Online presentation