INTRODUCTION
• Most common inherited peripheral neuropathy
• Also called peroneal muscular atrophy
• caused by abnormal peripheral myelin protein
• Slow progression with: Sensory loss, Muscular atrophy and weakness, Diminished deep tendon reflexes
HISTORY
• CMT was first described as a clinical entity in 1886
• By physicians Jean-Marie Charcot, Pierre Marie, and Howard Henry Tooth, who referred to it as “progressive muscular atrophy.”
CLASSIFICATION
Type I- demyelinating condition (more common)
• Autosomal dominant
• Onset in first or second decade of life
• Most commonly leads to cavus foot
• normal life expectancy
• motor involvement more profound than sensory
Type II
• Direct axonal death caused by Wallerian degeneration (not demyelination)
• Usually less disabled than Type I
• onset in second decade of life or later
• most commonly leads to flaccid foot
• CMT1: 50% of cases , characterized by demyelinating pathology, an autosomal dominant mode of inheritance
• CMT2: 15% to 30% of cases , characterized by axonal pathology, an autosomal dominant mode of inheritance
• CMTX: 10% to 15% of cases ,characterized by both demyelinating and axonal pathology. CMTX follows an X-linked mode of inheritance
• CMT3: CMT3 is uncommon ,characterized by demyelinating pathology with autosomal dominant inheritance. CMT3 has its onset in infancy
• CMT4: less than 10% of cases ,characterized by demyelinating pathology with an autosomal recessive mode of inheritance.
PATHOANATOMY
• affected muscles become weak
• peroneus brevis -is typically first and most profound
• results in muscle imbalance and varus deformity
• tibialis anterior -weakness results in footdrop
• intrinsic muscles of hand and foot- wasting of 1st dorsal interosseous in hands
GENETICS
• 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
ORTHOPAEDIC MANIFESTATIONS
• Pes cavovarus (bilateral)
• Claw toes
• Hip dysplasia
• Scoliosis
• Abnormal gait
• hand muscle atrophy and weakness
CLINICAL 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
• sensory deficits are variable
FAMILY HISTORY
• inquire about symptoms of neuropathy in relatives.
PHYSICAL EXAMINATION
• a complete neurological assessment is needed
• atrophy of weak muscles, reduction or loss of tendon reflexes, and skeletal deformities
• Assess gait
Foot deformities-
• Pes Cavus- with hammer toes or clawing of toes
• usually bilaterally and symmetric
• occurs due to- unopposed pull of peroneus longus- causing plantar flexion and compensatory hindfoot varus.
• initially flexible, but progresses to a rigid deformity
motor weakness-
• peroneal weakness
• weakest muscles around foot and ankle
• Tibialis anterior -weakens next, but typically stronger than the peroneals
• can lead to footdrop
• Tibialis posterior – stays strong for a prolonged period of time
• calf atrophy
• 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 deformity does not correct with Coleman block, this suggests hindfoot driven varus deformity.
• a rigid hindfoot will not correct into neutral
• Spine- scoliosis may be evident on Adam’s forward bend test
• Onset in the upper limbs with proximal muscle weakness is rare.
• Hand weakness manifests as difficulty in buttoning, zipping, and writing
EVALUATION
Electrophysiology(Electromyography (EMG) and NCS )
• crucial for confirming the diagnosis of neuropathy
• distinguishing between demyelinating and axonal types of CMT
• minimally invasive tests
• EMG and NCV are valuable for screening asymptomatic relatives of the index patient
Genetic testing
• standard for establishing a conclusive diagnosis,
• 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
DIFFERENTIAL DIAGNOSIS
• CMT must be differentiated from other conditions characterized by predominant distal weakness, muscle wasting, foot deformities
• acquired dysimmune neuropathies, neuropathies due to diabetes mellitus, nutritional deficiencies, vasculitis
TREATMENT
• predominantly rehabilitative and symptomatic
• currently no effective disease-modifying therapies
• a multidisciplinary healthcare team comprising neurologists, physiatrists, orthopedic surgeons, podiatrists, and physical and occupational therapists
PHARMACOTHERAPY
• Treatment remains largely symptomatic
• Musculoskeletal pain may be alleviated with acetaminophen or NSAIDs.
• Neuropathic pain may respond to tricyclic antidepressants
REHABILITATION
• Patients are at risk of developing reduced range of motion, contractures, and musculoskeletal deformities
• stretching, gripping exercises, aerobics, resistance training
• Physical therapy improves and maintains muscle strength and function, enhances joint flexibility and range of movement
Cavovarus Foot Deformity
• Foot deformities are a major source of disability in CMT
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
• degree of cavus – Ankle Xray lateral view by determining the Meary angle, the angle between the long axis of the first metatarsal and long axis of the talus; the normal angle is 0 degrees
• Nonoperative treatment of the cavovarus foot, including the use of serial casting and botulinum toxin, has generally been unsuccess ful
• Surgical procedures are of three types: soft tissue for flexible deformities (plantar fascia release, tendon release or transfer)
• Osteotomy for stiffer flexible or rigid deformities (metatarsal, midfoot, calcaneal)
• Joint stabilizing for completely rigid deformities (triple arthrodesis).
Hip dysplasias
• hip dysplasia is sometimes associated with CMT (typically less than 10%)
• may present during adolescence in ambulatory patients
• Treatment-pelvic osteotomy
Scoliosis
• often occurs in children with CMT ( ~ 10-20%)
• curve is usually mild to moderate and often does not require any treatment.
• nonoperative treatment with a brace is usually well tolerated
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