Charcot-Marie-Tooth disease (CMT) damages the peripheral nerves, the long cables that carry signals between your brain and your muscles, skin, and joints. It affects roughly 1 in 2,500 people, making it the most common inherited nerve disorder. Over time, CMT causes progressive muscle weakness and wasting in the feet, legs, and hands, along with sensory changes like numbness and difficulty feeling temperature or vibration.
How CMT Damages Your Nerves
Peripheral nerves have two key parts: the axon, which is the inner fiber that transmits electrical signals, and the myelin sheath, a fatty coating that insulates the axon and speeds up those signals. CMT attacks one or both of these structures depending on the type.
In CMT1, the most common form, genetic mutations disrupt the proteins that build and maintain myelin. Without intact myelin, nerve signals slow dramatically. A healthy nerve might conduct signals at 50 meters per second or faster, while nerves in CMT1 often drop below 38 meters per second. In CMT2, the axon itself degenerates while myelin stays relatively intact, so signals travel at closer to normal speed but reach fewer muscle fibers. In both cases, the end result is the same: muscles gradually lose their nerve supply and weaken. Research on over 200 patients confirmed that clinical weakness tracks with how many functional nerve fibers remain, not with how slowly signals travel. In other words, it’s the loss of working axons that causes disability, regardless of which type of CMT someone has.
What CMT Does to the Feet and Legs
The earliest and most visible effects of CMT appear in the feet and lower legs. Because the longest nerves are affected first, the small muscles in the feet weaken before anything else. This creates an imbalance: stronger muscles pull the foot into abnormal positions while weakened muscles can’t resist. The result is a cluster of deformities that worsen over time.
The most characteristic is pes cavus, an abnormally high arch that shifts your weight onto the ball and heel of the foot. The toes often curl into a “hammer” shape. The heel tilts inward (called hindfoot varus), and the forefoot drifts toward the midline. Studies using detailed foot measurements in CMT patients found that all of these deformities became more severe as the disease progressed. The combination makes walking increasingly unstable. Ankles roll easily, blisters and calluses form in unusual spots, and finding shoes that fit becomes a constant challenge.
As the calf and shin muscles atrophy, the lower legs can take on a tapered shape sometimes described as an “inverted champagne bottle,” where the thigh stays relatively normal but the calf thins noticeably. Foot drop, the inability to lift the front of the foot during a step, develops when the shin muscles weaken enough. This forces a high-stepping gait to avoid tripping.
Effects on the Hands and Arms
CMT follows a pattern: it starts at the extremities and works inward. After the feet and legs, the hands and forearms are next. Grip strength fades, fine motor tasks like buttoning a shirt or turning a key become harder, and the small muscles between the fingers may visibly thin. This typically lags behind the leg symptoms by years or even decades, and severity varies widely from person to person.
Sensory Changes and Pain
CMT isn’t just a motor disease. Sensory nerves are affected too, which can cause numbness, tingling, and reduced ability to feel heat, cold, or touch. Vibration sense and proprioception (the awareness of where your body is in space) often diminish, which compounds the balance problems already caused by muscle weakness. Some people with CMT also experience nerve pain, though it tends to be less prominent than the motor symptoms.
When Symptoms Typically Appear
Most people with CMT notice symptoms during childhood or adolescence, though the timeline varies by subtype. CMT1 often becomes apparent in the first or second decade of life. CMT2 can show measurable gait differences even earlier. One study tracking children found that by age 3, kids with CMT2 already tended to walk more slowly than their peers, while those with CMT1 were still keeping pace at that age. As healthy children naturally walk faster and take longer strides with growth, children with both CMT subtypes fell further behind over time, lacking the normal increase in walking speed that comes with development.
CMT is progressive but usually slow. Most people remain ambulatory throughout life, and life expectancy is generally normal. Progression isn’t linear, though. Some people experience stretches of relative stability followed by periods of noticeable decline, and severity can differ significantly even among family members who carry the same mutation.
How CMT Is Inherited
CMT is genetic, and over 100 different gene mutations can cause it. The inheritance pattern depends on the subtype.
- Autosomal dominant (CMT1 and most CMT2): Only one copy of the mutated gene is needed. If a parent has it, each child has a 50% chance of inheriting it.
- Autosomal recessive (CMT4 and some CMT2 subtypes): Both parents must carry a copy of the mutation. This pattern accounts for a small minority of cases, likely under 4% in non-consanguineous populations.
- X-linked (CMTX): The mutation sits on the X chromosome. Males, who have only one X, tend to be more severely affected. Fathers cannot pass X-linked CMT to sons, but all daughters of an affected father will carry the mutation, often with milder symptoms.
Some cases arise from new, spontaneous mutations with no family history at all.
How CMT Is Diagnosed
Diagnosis usually starts with a neurological exam, where a doctor tests reflexes, muscle strength, and sensation. The key diagnostic tool is a nerve conduction study, which measures how fast electrical signals travel along your nerves. In CMT1, motor nerve conduction velocity in the forearm typically falls below 38 meters per second, well under the normal range. CMT2 shows closer-to-normal speeds but reduced signal strength, reflecting fewer working nerve fibers. Genetic testing can then confirm the specific mutation and subtype.
Managing CMT Day to Day
There’s no cure for CMT, but a combination of physical support and targeted exercise can meaningfully slow functional decline and maintain quality of life.
Orthotics are the front line. Simple shoe inserts may be enough in early stages when foot deformities are mild. As weakness progresses, ankle-foot orthoses (AFOs) become important. These brace the ankle to compensate for foot drop, stabilize the knee during standing and walking, and help with balance. Custom-fitted orthoses tend to be more comfortable and produce better long-term compliance than off-the-shelf options.
Rehabilitation programs typically focus on four areas: strengthening exercises that target the muscles still under good nerve control, stretching to prevent joints from tightening into fixed positions, aerobic conditioning to maintain cardiovascular fitness and slow further muscle loss, and balance training to improve proprioception and reduce falls. These aren’t optional extras. Consistent exercise programs help preserve mobility and function for years longer than going without.
Surgery becomes relevant when foot deformities are severe enough that bracing can’t compensate. In earlier stages, when the foot is still flexible, surgeons can rebalance the foot using tendon transfers and bone cuts that preserve joint motion. The current consensus favors early surgical intervention to prevent deformities from becoming rigid. In advanced cases where the foot has stiffened into a fixed position, more complex procedures including joint fusion may be necessary.
Medications That Can Worsen CMT
Certain drugs can accelerate nerve damage in people with CMT. A systematic review of the evidence found strong support that vincristine, a chemotherapy drug, can trigger unusually severe nerve toxicity in CMT patients. Paclitaxel, another chemotherapy agent, may pose a similar risk. For other medications commonly flagged in older lists (certain antibiotics, heart rhythm drugs), the same review found no convincing evidence of increased danger. Still, if you have CMT and are starting any new medication, making your diagnosis known to every prescribing doctor is a practical safeguard.