Charcot-Marie-Tooth Disease

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Definition And Epidemiology

Charcot-Marie-Tooth disease is the most common hereditary neuropathy.
It is the most common peripheral neuropathy overall in children.
It is classified as a primary hereditary neuropathy affecting the peripheral nerves.
The disease primarily affects the lower motor neuron unit.
It is also referred to as hereditary motor sensory neuropathy.
The overall prevalence of the most common demyelinating variant is approximately 3.8 cases per 100,000 population.
It accounts for more than 50 percent of all hereditary motor sensory neuropathy cases.

Clinical Manifestations

Onset And Progression

The disease has an insidious onset.
It follows a slowly progressive course over many years.
Most patients remain asymptomatic until late childhood or early adolescence.
Young children sometimes manifest gait disturbances as early as the second year of life.

Motor Symptoms

Weakness predominantly affects the distal muscles.
The peroneal and tibial nerves are the earliest and most severely affected.
Affected children are often described as being clumsy.
They experience progressive gait difficulties, frequent falls, and tripping over their own feet.
Progressive weakness of ankle dorsiflexion leads to eventual foot drop.
The lower legs develop marked thinning, leading to a classic 'stork leg' appearance.
This unique atrophy is also described as an 'inverted champagne bottle' appearance.
Upper limb involvement occurs later in the disease course.
This includes atrophy of the thenar and hypothenar muscles.
Advanced cases demonstrate clawing of the fingers and contractures of the wrists.
Proximal muscle weakness is a late manifestation and is usually mild.

Sensory And Autonomic Symptoms

Prominent sensory signs are present even in the absence of prominent sensory symptoms.
Sensory involvement mainly affects large, myelinated nerve fibers.
This leads to a loss of proprioceptive information and vibratory sense.
The threshold for pain and temperature can also increase.
Children may complain of tingling or burning sensations in the feet, but pain is rare.
Autonomic manifestations may be expressed as poor vasomotor control.
This can lead to blotching or pallor of the skin of the feet and inappropriately cold feet.

Associated Features

Pes cavus foot deformities are a hallmark and prominent clinical feature.
Hammer toe deformities are also commonly observed.
Deep tendon reflexes are hyporeflexic or completely depressed due to lower motor neuron involvement.
Reflexes are typically lost distally.
Peripheral nerves often become palpably enlarged at an early age.
A positive family history is a critical clue pointing towards an inherited neuropathy.

Classification And Genetics

The disease exhibits vast genetic heterogeneity with more than 140 genes implicated.
The classification is broadly divided into demyelinating, axonal, and severe infantile forms.

Disease Subtype	Inheritance Pattern	Gene Or Locus	Pathophysiology And Clinical Features
Charcot-Marie-Tooth 1A	Autosomal dominant	Duplication at 17p11.2 (PMP22)	Most common subtype (70% of CMT1). Uniform conduction velocity slowing below 38 m/s. Demyelinating pattern.
Charcot-Marie-Tooth 1B	Autosomal dominant	Mutation at 1q21-q23 (MPZ)	Demyelinating pattern. Gene product is myelin protein zero.
Charcot-Marie-Tooth 2A	Autosomal dominant	Mutation at 1p36 (MFN2)	Most common axonal form. Relatively normal nerve conduction velocities. Predominantly reduced action potential amplitudes.
Charcot-Marie-Tooth 3 (Dejerine-Sottas)	Autosomal dominant or recessive	17p11.2 (PMP22) or 1q21-q23 (MPZ)	Severe demyelinating form. Onset in infancy or the first year of life. Very low motor conduction velocity.
Charcot-Marie-Tooth 4	Autosomal recessive	Multiple genes (e.g. GDAP1)	Childhood onset. Usually severe presentation. Contains both demyelinating and axonal types.
Charcot-Marie-Tooth X	X-linked dominant or recessive	Mutation at Xq13 (Connexin 32)	Axonal and demyelinating features. Males are more severely affected. Central nervous system involvement is common.

Diagnostic Evaluation

Clinical And Electrophysiological Studies

A detailed clinical history is required to identify insidious distal weakness, foot deformities, and familial patterns.
Electrophysiological studies, including nerve conduction velocity and electromyography, are the primary modalities to classify the disease.
These studies provide objective data to distinguish demyelinating forms from axonal forms.

Electrophysiological Property	Demyelinating Pattern (e.g. CMT 1 and 3)	Axonal Pattern (e.g. CMT 2)
Distal Latency	Increased (prolonged).	Normal.
Conduction Velocity	Decreased (reduced).	Normal.
Action Potential Amplitude	Normal.	Decreased (reduced).
Conduction Block	Absent in hereditary forms.	Absent.
Temporal Dispersion	Absent in hereditary forms.	Absent.

Genetic And Histological Testing

Genetic testing is useful and necessary for confirming the exact genetic diagnosis and subtype.
The definitive molecular genetic diagnosis may easily be made using a blood sample.
A sural nerve biopsy is diagnostic and reserved for cases where genetic testing is inconclusive.
Biopsies of demyelinating forms reveal characteristic onion bulb formations.
These formations represent cycles of demyelination and remyelination using Toluidine blue staining.
This pathologic finding is termed interstitial hypertrophic neuropathy.
Biopsies of axonal forms reveal axonal degeneration rather than primary demyelination.
The cerebrospinal fluid protein may be elevated, but no cells appear in the fluid.

Differential Diagnosis

Distinguishing Charcot-Marie-Tooth disease from other acute and chronic neuropathies is essential.

Condition	Distinguishing Clinical Features
Friedreich Ataxia	Shows areflexia and distal weakness similar to Charcot-Marie-Tooth disease. Differentiated by clear ataxia, loss of joint position sense, and a sensory neuropathy pattern on neurophysiology.
Guillain-Barré Syndrome	Acute onset over hours to days. Presents with ascending, bilaterally symmetrical flaccid weakness. Frequently has an antecedent infectious trigger.
Chronic Inflammatory Demyelinating Polyneuropathy	Subacute to chronic progression. Involves both proximal and distal weakness. Concomitant sensory loss is present.
Spinal Muscular Atrophy	Presents with tongue fasciculations and polyminimyoclonus. Face is relatively spared. Sensory pathways are unaffected.

Management And Genetic Counseling

Supportive care remains the standard of therapy for this disease.
There is currently no effective specific pharmacologic or genetic treatment available in clinical practice.

Physical Therapy And Orthotics

Regular physical therapy is required to maintain mobility.
It is crucial for preventing contractures and managing progressive distal weakness.
Progressive resistance exercise for foot dorsiflexion may attenuate the progression of weakness.
The lower legs should be protected from traumatic injury.
Orthotic appliances are frequently required to stabilize the ankles and support ambulation.
Stiff boots that extend to the midcalf often suffice in the early stages of the disease.
Lightweight plastic splints, which can be worn inside socks, are custom-made to extend beneath the foot and around the back of the ankle.
External short-leg braces or ankle-foot orthotics may be required when foot drop becomes complete.

Pharmacological And Surgical Interventions

Burning paresthesias of the feet are uncommon but can be abolished by administering phenytoin, carbamazepine, or gabapentin.
Compression neuropathy during sleep may be prevented by placing soft pillows beneath or between the lower legs.
Severe foot deformities and hand deformities may require surgical management.
Soft tissue release, bony foot surgery, or surgical fusion of the ankle may be considered in cases of progressive foot deformity.

Counseling

Genetic counseling must be offered to the patient’s family.
Discussions should cover inheritance patterns, recurrence risks, and options for prenatal diagnosis.