Charcot-Marie-Tooth Disease

• most common Hereditary motor-sensory neuropathy (HMSN)
• life expectancy, intellectual function are normal
• male > female, females more severe
• affects 1/2500 people
• 17 genetic vairiants have thus far been determined.  HMSN Type 1=AD form is a duplication of chromosome 17p11.2.  HMSN Type 2=AR, neuronal form
• can be autosomal-dominant, autosomal-recessive or X-linked
• diagnosis is made based on clinical appearance of the foot and positive family history. There is no definitive diagnostic technique.

CMT Anatomy

• intrinsic foot muscles affected first followed by peroneus brevis, >>anterior tibialis >> EDC
• Forefoot equinus develops as a result of an imbalance between the tibialis anterior muscle and the peroneus longus muscle. 
• posterior compartment and peroneus longus pull foot into forefoot and ankle equinus
• The peroneus longus tendon courses from plantar lateral to medial and inserts into the base of the first metatarsal.  It opposes the action of the tibialis anterior muscle dorsally.  In CMT disease, the tibialis anterior and peroneus brevis muscles are weak.  The peroneus longus is unopposed and plantarflexes the first ray, creating forefoot equinus

CMT Clinical Evaluation

• present 1-3 decade, +family hx
• slowly progressive distal muscular weakness and atrophy with minor deficits in sensation
• c/o deformity and awkward gait, muscle cramping
• symmetric elevation of arches(pes cavus), plantar flexed first ray, hindfoot varus, claw toes, decreased ankle jerk, flatfoot or heal-toe gait.  May have callosities beneath MT heads
• Coleman Block test=plantar-flex first mt is allowed to hang free from block beneath foot.  If supple deformity the hindfoot corrects.
• evaluation for developmental hip dysplasia indicated(Van Erve J Pediatric Orthop 19:92;1999)

CMT Treatment / Classification

• fixed vs flexible
• Flexible=bracing vs plantar fascia release, closing wedge dorsiflexion osteotomy of 1st mt, calcaneal sliding and closing wedge osteotomy, transfer of peroneus longus into peroneus brevis a the level of the distal fibula, +/- TAL (Roper JBJS 71B:17;1989)
• Fixed=triple arthrodesis with transfer of posterir tib tendon throught the interosseous membrane and a TAL  (Wetmore JBJS 71A:417;1989)

CMT Differential Diagnosis

• Amyotrophic lateral sclerosis (Lou Gerig's disease)
• Huntington's chorea
• Friedreich's ataxia
• also see Cavovarus foot

CMT References

Alexander IJ, Johnson KA: Assessment and management of pes cavus in Charcot-Marie-Tooth disease.  Clin Orthop 1989;246:273-281.

Wetmore RS, Drennan JC: Long-term results of triple arthrodesis in Charcot-Marie-Tooth disease.  J Bone Joint Surg 1989;71A:417-422.

Holmes JR, Hansen ST Jr: Foot and ankle manifestations of Charcot-Marie-Tooth disease.  Foot Ankle 1993;14:476-486