Charcot-Marie-Tooth Disease

Definition And Epidemiology

• Charcot-Marie-Tooth (CMT) disease is the most common hereditary neuropathy.
• It is the most common peripheral neuropathy overall in children.
• Classified as a primary hereditary neuropathy affecting the peripheral nerves (lower motor neuron unit).

Clinical Manifestations

• Onset And Course: Insidious onset with a slowly progressive course over years.
• Motor Symptoms:
  • Predominantly distal weakness and wasting.
  • Progressive gait difficulties and frequent falls due to twisting of ankles.
  • ‘Stork leg’ appearance resulting from marked thinning of the lower legs.
  • Upper limb involvement includes atrophy of thenar and hypothenar muscles along with clawing of fingers.
• Sensory Symptoms: Prominent sensory signs are present in the absence of sensory symptoms.
• Skeletal Deformities: Foot deformities are a hallmark and prominent clinical feature.
• Reflexes: Hyporeflexia or completely depressed deep tendon reflexes due to lower motor neuron involvement.
• Family History: A positive family history is a critical clue pointing towards an inherited neuropathy.

Classification And Electrophysiology

CMT presents as a polyneuropathy (involvement of $\ge$ 2 nerves). It is evaluated and classified primarily using electrophysiological studies (Nerve Conduction Studies and Electromyography).

• Charcot-Marie-Tooth disease types 1 and 3 are classical examples of demyelinating hereditary neuropathies.
• Electrophysiological studies provide objective data to distinguish demyelinating forms of CMT from axonal forms.

Electrophysiological Characteristics Of Neuropathies

Compound Muscle Action Potential Property	Demyelinating Pattern (e.g., CMT 1 & 3)	Axonal Pattern
Distal Latency	Increased	Normal
Conduction Velocity	Decreased	Normal
Amplitude	Normal	Decreased
Conduction Block	Present (in acquired causes)	Absent
Temporal Dispersion	Present (in acquired causes)	Absent

Diagnosis

• Clinical Evaluation: Detailed history identifying insidious distal weakness, foot deformities, and family history.
• Electrophysiological Studies: Nerve Conduction Velocity (NCV) and Electromyography (EMG) determine if the abnormality is axonal or demyelinating.
• Genetic Testing: Useful and necessary for confirming the exact genetic diagnosis and subtype of CMT.

Differential Diagnosis

Charcot-Marie-Tooth disease must be differentiated from other acquired and hereditary causes of peripheral neuropathy and acute flaccid paralysis.

Clinical Clues To Differentiate Common Neuropathies

Condition	Onset, Duration And Progression	Pattern Of Weakness	Associated Features
Hereditary Neuropathies (CMT)	Insidious onset, gradually progressive over years	Distal more than proximal	Muscle atrophy, prominent foot deformities
Guillain-Barré Syndrome (GBS)	Acute onset	Ascending, bilaterally symmetrical flaccid weakness	Predominantly distal, antecedent infection
Chronic Inflammatory Demyelinating Polyneuropathy (CIDP)	Subacute to chronic	Both proximal and distal weakness	Concomitant sensory loss

Etiological Differentials For Peripheral Neuropathies

Category	Examples
Primary Hereditary Neuropathies	Hereditary neuropathy with liability to pressure palsies, Hereditary sensory and autonomic neuropathies (HSAN), Distal hereditary motor neuropathies, Hereditary neuralgic amyotrophy.
Multisystem Hereditary Disorders	Leukodystrophies, Krabbe disease, Adrenoleukodystrophy, Metachromatic leukodystrophy, Porphyria, Ataxia telangiectasia, Friedrich ataxia.
Acquired Polyneuropathies	Guillain-Barré syndrome, CIDP, Diphtheria, Toxic neuropathies (e.g., arsenic, lead, chemotherapy drugs), Vitamin B12 or E deficiency.

Management And Counseling

• Supportive Care: Supportive care remains the standard of therapy for CMT.
• Physical Therapy: Regular physical therapy is required to maintain mobility, prevent contractures, and manage the progressive distal weakness.
• Orthopedic Intervention: Bracing, orthotics, or surgical management may be required for severe foot deformities (‘stork leg’) and hand deformities (clawing of fingers).
• Genetic Counseling: Genetic counseling must be offered to the patient’s family to discuss inheritance patterns, recurrence risks, and prenatal diagnosis options.