Charcot-Marie-Tooth (CMT) disease is a group of inherited disorders that damage the peripheral nerves outside the brain and spinal cord. Also known as hereditary motor and sensory neuropathy (HMSN), this condition causes nerve damage primarily in the arms and legs. This results in muscle weakness and reduced sensation in these limbs. The initial signs of CMT emerge during adolescence or early adulthood but can appear later in life.
Genetic Origins of CMT
CMT stems from inherited mutations in genes responsible for peripheral nerve structure and function. These nerves have axons that transmit electrical signals and are often covered by a myelin sheath that speeds up transmission. Genetic mutations can damage the axon or impair the myelin sheath, disrupting communication between the brain and limbs.
The specific gene mutation determines the CMT type, with over 100 implicated genes creating many variations. The condition can be passed down in an autosomal dominant pattern, requiring a mutated gene from one parent, or an autosomal recessive pattern, requiring a mutated gene from both parents.
Common Signs and Symptoms
The signs of CMT vary widely, even among family members, but begin in the feet and legs. A primary motor symptom is weakness in the muscles of the feet and lower legs, causing “foot drop”—a difficulty lifting the front of the foot. This leads to a high-stepping gait and frequent tripping. Muscle atrophy is also common, sometimes giving the lower legs an “inverted champagne bottle” appearance.
As the disease progresses, weakness and atrophy can spread to the hands and arms, making fine motor tasks challenging. Sensory symptoms are also frequent, including a reduced ability to feel heat, cold, and touch, as well as numbness in the feet and hands. This loss of sensation contributes to balance problems because the body’s ability to sense its position is diminished.
A distinctive feature of CMT is the development of foot deformities like high arches (pes cavus) and curled toes (hammertoes). In some individuals, the opposite can occur, leading to very flat feet. Spinal deformities such as scoliosis and hip displacement can also develop in some people with CMT.
The Diagnostic Process
Diagnosing Charcot-Marie-Tooth disease begins with a physical examination and a review of family medical history. A neurologist will look for evidence of muscle weakness, decreased muscle mass, reduced tendon reflexes, and sensory loss in the extremities. The presence of characteristic foot deformities like high arches or hammertoes is also an indicator.
To evaluate nerve function, doctors perform nerve conduction studies (NCS). This test measures the speed and strength of electrical signals traveling through peripheral nerves, which may be slower or weaker in CMT. This can be complemented by electromyography (EMG), which assesses the electrical activity of muscles to detect evidence of nerve damage.
Genetic testing is often used to confirm the diagnosis. A blood test can identify the specific mutation in one of the genes known to cause CMT. Pinpointing the genetic cause confirms the diagnosis and helps in understanding the specific CMT type and its inheritance pattern, which is valuable for family planning.
Symptom Management and Therapies
There is no cure for CMT, so treatment focuses on managing symptoms and maintaining mobility. Physical therapy plays a large role, with exercises designed to maintain muscle strength, improve flexibility, and enhance balance. Regular, low-impact exercise helps combat muscle weakness and fatigue without putting excessive strain on the body.
Occupational therapy helps individuals adapt to the challenges of daily living. Therapists provide strategies and assistive devices to help with tasks that become difficult due to hand weakness, such as buttoning clothes or writing. This support helps people maintain their independence.
To address mobility issues like foot drop and ankle instability, orthopedic devices are prescribed. Ankle-foot orthoses (AFOs) are braces worn inside shoes that provide support to improve gait and reduce the risk of falls. Custom shoes or inserts can also accommodate foot deformities and provide better stability. When pain results from postural changes, a combination of physical therapy and pain-relieving medications may be used.
Living with Charcot-Marie-Tooth Disease
The progression of CMT is slow, and it does not impact a person’s normal life expectancy. Symptom severity varies greatly, with some individuals experiencing minor limitations while others face more significant physical challenges. The focus of long-term care is on adapting to changes and maximizing quality of life.
Managing the condition involves a collaborative care team that may include a neurologist, physical and occupational therapists, and orthotists. Regular follow-ups with this team allow for adjustments to the management plan as the condition evolves. This approach helps in addressing new symptoms and maintaining function.
Support systems are a valuable resource for individuals and families affected by CMT. Patient advocacy organizations and support groups provide a community for sharing experiences, information, and coping strategies. Connecting with others who understand the condition can reduce feelings of isolation and empower individuals.