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Introduction
  • A hereditary motor sensory neuropathy (HMSN) that has two forms resulting in muscles weakness and sensory changes
    • also known as peroneal muscular atrophy
  • Epidemiology
    • most common inherited progressive peripheral neuropathy
    • 40:100,000
  • Pathophysiology
    • HMSN Type I
      • abnormal myelin sheath protein is the basis of this degenerative neuropathy.
      • results in a combination of motor and sensory disturbances. 
    • HSMN Type 2
      • intact myelin sheath with wallerian axonal degeneration that results in mild sensory and motor conduction velocities. 
    • pathoanatomy
      • affected muscles become weak 
        • peroneus brevis  
          • peroneal involvement is typically first and most profound
          • results in muscle imbalance and varus deformity
        • tibialis anterior
          • weakness results in dropfoot
        • intrinsic muscles of hand and foot
          • check for wasting of 1st dorsal interosseous in hands
  • Genetics
    • inheritance
      • autosomal dominant duplication of chromosome 17 (most common)  
        • codes for peripheral myelin protein 22 (PMP 22) expressed in Schwann cells (most common) 
        • X-linked connexin 32
      • may also be
        • autosomal recessive
        • X-linked
  • Orthopedic manifestations  
    • pes cavovarus 
    • hammer toes 
    • hip dysplasia 
    • scoliosis
    • hand muscle atrophy and weakness
Classification
  • The major categories of Charcot-Marie-Tooth are
    • Types 1 through 7
    • an X-linked category
 Classification of CMT
Type I

demyelinating condition that slows nerve conduction velocity 
Characteristics:
   1. autosomal dominant
   2. onset in first or second decade of life
   3. most commonly leads to cavus foot
   4. normal life expectancy
   5. motor involvement more profound than sensory

Type II Direct axonal death caused by Wallerian degeneration (not demyelination) 
Characteristics:
   1. Usually less disabled than Type I
   2. onset in second decade of life or later
   3. most commonly leads to flaccid foot
 
Presentation
  • Symptoms
    • motor deficits
      • initial symptoms are distal weakness and atrophy of the distal muscles
      • instability during gait
      • clumsiness
      • frequent ankle sprains
      • difficulty climbing stairs
    • lateral foot pain 
    • sensory
      • sensory deficits are variable
  • Physical exam
    • lower extremity
      • cavovarus foot
        • (similar to Freidreich's ataxia) with hammer toes or clawing of toes
        • usually bilaterally and symmetric. 
        • occurs due to 
          • unoposed pull of peroenus longus
            • causing plantarflexion of the first ray and compensatory hindfoot varus. 
          • initially flexible, but progresses to a rigid deformity
      • motor weakness
        • peroneal weakness
          • weakest muscles around foot and ankle
        • anterior tibialis 
          • weakens next, but typically stronger than the peroneals
            • can lead to drop foot in swing initially and later to a fixed equinus
        • posterior tibialis
          • stays strong for a prolonged period of time
        • calf atrophy
          • rarely significant present
        • weak intrinsics
          • including weak EDB and EHB
        • clawtoes
      • hyporeflexia or areflexia
      • Coleman block test
        • test to determine if hindfoot varus deformity is secondary to plantar-flexed first ray vs an independent component. 
          • If deformity corrects with Coleman block, this suggests a forefoot driven varus deformity. 
          • If defromity does not correct with Coleman block, this suggests hindfoot driven varus defromity. 
          • a rigid hindfoot will not correct into neutral
    • upper extremity
      • intrinsic wasting of hands
      • weak pinch and grasp
    • spine
      • scoliosis may be evident on Adam's forward bend test
Studies
  • EMG
    • low nerve conduction velocities with prolonged distal latencies are noted in peroneal, ulnar, and median nerves
    • can also see low amplitude nerve potentials due to axonal loss 
  • Genetic Testing
    • Key component for diagnosis of CMT
    • DNA analysis
      • PCR analysis used to detect peripheral myelin protein 22 (PMP22) gene mutations
    • chromosomal analysis
      • duplication on chromosome 17 seen in autosomal dominant (most common) form
Cavus Foot Deformity
  • Introduction
    • evaluation and treatment follows same principals for cavovarus foot  
    • pathophysiology
      • plantar flexed 1st ray is initial deformity 
      • cavus caused by 
        • peroneus longus (more normal) overpowering weak tibialis anterior  
        • weak intrinsics and contracted plantar fascia
    • varus caused by tibialis posterior (normal) overpowering weak peroneus brevis and longus 
  • Treatment
    • nonoperative
      • accomodative shoe wear
        • indications
          • rarely sufficient except in mild deformity
      • full-length semi-rigid insole orthotic with a depression for the first ray and a lateral wedge 
        • indications
          • mild cavus foot deformity in adult (not indicated in children)
      • supramalleolar orthosis (SMO) 
        • indications
          • more severe cavovarus deformity recalcitrant to shoewear accomodations
      • ankle foot orthosis (AFO)
        • indications
          • may be needed if equinus also present, resulting in equinocavovarus foot deformity
          • works best if equinus is a dynamic defomrity (not rigid)
      • lace-up ankle brace and/or high-top shoe or boots
        • indications
          • may consider in moderate deformities when patient does not tolerate the more rigid bracing with an SMO or AFO
    • operative
      • soft tissue reconstruction
        • indications
          • flexible deformity in adolescents with closed physes 
          • failed conservative management of fixed deformities
        • performed with a combination of the following procedures
          • plantar release (plantar fascia +/- Steindler stripping, i.e. release of short flexors off the calcaneus)
            • indications
              • cavus
          • peroneus longus to brevis transfer
            • indications
              • plantar flexed first ray
            • rationale
              • decreases plantarflexion force on first ray without weakening eversion
          • posterior tibial tendon transfer
            • indications
              • muscle imbalance: posterior tibialis typically is markedly stronger than evertors and maintains strength for a long time in most cavovarus feet
              • may consider transfer of posterior tibialis to dorsum of foot if severe dorsiflexion weakness of anterior tibialis
          • lengthening of gastrocnemius or tendoachilles (TAL)
            • indications
              • true ankle equinus
            • outcomes
              • gastrocnemius recession produces less calf weakness and can be combined with plantar release simultaneously (TAL should be staged several weeks after plantar release)
          • Jones transfer(s) of EHL to neck of 1st MT and lesser toe extensors to 2nd-5th MT necks
            • indications
              • toe clawing combined with cavus foot  
              • performed if the indication is met and time permits
      • 1st metatarsal dorsiflexion osteotomy 
        • indications
          • flexible hindfoot cavus deformities (normal Coleman block test and/or passive hindfoot eversion past neutral)  
      • triple arthrodesis, lateral calcaneal slide or closed-wedge osteotomy
        • indications
          • performed if deformity does not correct with Coleman block test. 
Claw Toes Deformity
  • Introduction
    • ankle dorsiflexion weakness may result in the recruitment of toe extensors for assistance
      • in the setting of intrinsic muscle weakness, increased toe extensor activity can lead to claw toe deformity, which becomes rigid with time
  • Treatment
    • operative
      • Jones procedure 
        • indications
          •  for symptomatic claw toe deformity which has failed non-operative measures
        • technique
          • transfers extensor tendons of the great and lesser toes to the metatarsal neck
          • goal is to increase contributions to ankle dorsiflexion and decrease clawing in order to relieve pain on the dorsum of the toes and the plantar aspect of the metatarsal heads
Hip dysplasias
  • Introduction
    • hip dysplasia is sometimes associated with CMT (typically less than 10%)
      • may present during adolescence in ambulatory patients
  • Treatment
    • pelvic osteotomy
      • indications
        • symptomatic hip dysplasia
      • outcomes
        • higher rate of sciatic nerve palsy after surgery
Scoliosis
  • Introduction
    • often occurs in children with CMT ( ~ 10-20%)
    • characteristic left thoracic and kyphotic curve distinguish from idiopathic scoliosis
  • Treatment
    • nonoperative
      • bracing
        • indications
          • bracing rarely effective so not typically used
    • operative
      • fusion and instrumentation
        • indications
          • progressive deformity with scoliosis > 50 degrees
 

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