Charcot-Marie-Tooth Disease
An inherited peripheral neuropathy causing progressive distal muscle weakness, atrophy, and sensory loss, classically featuring pes cavus and hammer toes.
Emergency Management: Acute respiratory failure in variants affecting the phrenic nerve (requires mechanical ventilation).
Charcot-Marie-Tooth (CMT) disease comprises a clinically and genetically heterogeneous group of inherited neuropathies affecting the peripheral nervous system. The hallmark of the disease is a length-dependent, progressive degeneration of motor and sensory nerves. It predominantly affects the distal extremities, leading to muscle weakness, atrophy, and sensory loss.
Detailed Overview
CMT is one of the most common inherited neurological disorders. It is typically divided into demyelinating (CMT1) and axonal (CMT2) forms based on electrophysiologic studies. Mutations in genes related to myelin structure (e.g., PMP22) or axonal transport lead to impaired nerve conduction and subsequent length-dependent denervation. This results in the characteristic 'stork leg' appearance, pes cavus, and frequent tripping.
Epidemiology & Demographics
Prevalence is approximately 1 in 2,500 individuals globally. It affects both genders equally. Onset is typically in the first or second decade of life for CMT1, while CMT2 may present later.
Etiological Mechanism
CMT is genetically heterogeneous. CMT1A (most common, ~60% of cases) is caused by a 1.5 Mb duplication on chromosome 17p11.2 encompassing the PMP22 gene. CMTX1 is X-linked, caused by GJB1 mutations. CMT2 involves mutations in genes like MFN2 (mitofusin-2).
Primary Causes
Inherited gene mutations disrupting myelin formation, maintenance, or axonal function in peripheral nerves. Most common inheritance patterns are autosomal dominant (CMT1, CMT2), but X-linked and autosomal recessive forms exist.
In demyelinating CMT (e.g., CMT1A), overexpression of the PMP22 protein disrupts myelin compaction and Schwann cell function, leading to repeated cycles of demyelination and remyelination ('onion bulb' formation). This slows nerve conduction velocity (NCV). Secondary axonal loss follows. In axonal CMT (e.g., CMT2), the primary defect is in axonal structure or transport (e.g., mitochondrial dynamics via MFN2), leading to Wallerian degeneration and reduced compound muscle action potential (CMAP) amplitudes with relatively preserved NCV.
Diagnostic Criteria & Guidelines
Diagnosis is based on a characteristic clinical phenotype (distal weakness, areflexia, pes cavus), family history, electrodiagnostic testing (NCV < 38 m/s in upper limbs for CMT1; > 38 m/s for CMT2), and is confirmed by genetic testing.
Management is supportive and multidisciplinary. Physical therapy (daily heel cord stretching) and occupational therapy. Use of ankle-foot orthoses (AFOs) to manage foot drop. Neuropathic pain may be treated with Gabapentin (300 mg TID, titrated up to 3600 mg/day) or Pregabalin (50-75 mg BID, titrated up to 600 mg/day). Avoid neurotoxic drugs (e.g., vincristine, taxanes).
Second-Line & Adjunctive Therapy
For severe neuropathic pain refractory to first-line agents, Duloxetine (30-60 mg PO daily) or Tricyclic Antidepressants (e.g., Amitriptyline 10-25 mg PO QHS) can be utilized. High-dose Ascorbic acid has been trialed for CMT1A but lacked significant clinical benefit in major RCTs.
Surgical & Procedural Management
Orthopedic surgery for severe foot deformities: plantar fascia release, Achilles tendon lengthening, metatarsal osteotomies, or triple arthrodesis for rigid deformities.
Patient Counseling & Advice
Educate that CMT is slowly progressive but does not typically shorten lifespan. Discuss inheritance patterns and offer genetic counseling for family planning. Emphasize the importance of avoiding neurotoxic medications.
Follow-Up & Monitoring Schedule
Annual multidisciplinary clinic visits including neurology, physical therapy, and orthotics assessment. Assess for progression of muscle weakness using the CMT Neuropathy Score (CMTNS).
Preventive Strategies
No cure or prevention for the onset of the disease. Preimplantation genetic diagnosis (PGD) is an option for known familial mutations.
Normal life expectancy for most types. Ambulation is usually maintained, though assistive devices (AFOs, canes, wheelchairs in severe cases) may be needed later in life.