Charcot-Marie-Tooth disease

Overview

Charcot-Marie-Tooth (CMT) is the most common inherited neurological disorder of the peripheral nerve, affecting approximately 150,000 Americans. It was named after the three doctors — Jean-Martin Charcot, Pierre Marie and Howard Henry Tooth — who first identified the condition in 1886. CMT is considered a peripheral neuropathy because it damages the peripheral nerves, which are located outside the brain and spinal cord and control sensory information and muscle function.

CMT causes a slow degeneration of the muscles in the foot, lower leg, hand and forearm, as well as a loss of sensation in the limbs, fingers and toes. People affected with CMT eventually lose normal use of their feet, legs, hands and arms.

There are many different types of CMT. Each type is distinguished by the age of onset, inheritance pattern, severity and the abnormal gene that causes it. More than 30 genes have been implicated in CMT. The age of onset for the most common forms of CMT is typically childhood or adolescence.

In different types of CMT, peripheral nerve damage can be caused by defects in genes coding for proteins affecting axons, or by defects in genes coding for proteins affecting the insulating myelin coating around each axon, or both.

CMT usually is not life threatening, and very rarely affects a person's brain. Although there's currently no cure for the condition, there are treatments that can effectively manage its symptoms.

Signs & symptoms

Because there are many types of CMT, each person will experience symptoms differently. However, some of the most common symptoms include:

• Slowly progressing weakness and wasting in the foot, lower leg, hand and forearm muscles.
• Loss of sensation in the limbs, fingers and toes, which may cause decreased sensitivity to heat, touch and pain in the feet and lower legs.
• High arched foot, one of the first signs of the disorder.
• "Foot drop," caused by weakness in the feet and ankles. People with foot drop may have trouble lifting the foot at the ankle, so that toes point downward during walking. Foot drop causes a person to trip frequently and develop an abnormal gait.
• Loss of hand function.
• Contractures, a tightening of the joints that may cause deformities of the feet and hands.

Diagnosis

The doctor will start by conducting an extensive physical exam and history to check for any signs of CMT, such as foot deformities and muscle weakness. The doctor will also check for signs of nerve damage related to CMT or another hereditary neuropathy. You will be asked about your family history, and whether anyone else in your family has CMT or symptoms related to CMT.

If the doctor suspects your child has CMT, the following tests may also be recommended:

Electrodiagnostic Tests

This test consists of two parts: nerve conduction studies and electromyography (EMG). During nerve conduction studies, electrodes are placed on the skin over a peripheral motor or sensory nerve. These electrodes produce a small electric shock that may cause mild discomfort. This electrical impulse stimulates sensory and motor nerves.

EMG involves inserting a needle electrode through the skin to measure the bioelectrical activity of muscles and whether peripheral nerves have been damaged.

Genetic Testing

These tests, performed with a blood sample, are designed to detect the most common genetic defects known to cause CMT. In addition to helping confirm a diagnosis, genetic testing is available to parents who are concerned that they may pass CMT-causing genes on to their children.

Treatment

Although there is currently no cure for CMT, there are treatments available to help manage its complications and improve patients' quality of life. Therapies may include physical therapy, occupational therapy, braces and other mobility devices, as well as orthopedic surgery.

Physical and Occupational Therapy

Physical and occupational therapy is an essential part of CMT therapy. This may involve muscle strength and stamina training, muscle and ligament stretching and moderate aerobic exercise. The goal is to preserve function and maintain comfort. Your child's stretching program will be monitored by the physiotherapist, but needs to become part of the family's daily routine.

Many factors contribute to the tendency for joints to get tight or "contracted." These include the muscle becoming less elastic due to limited use and positioning, or the muscles around a joint becoming out of balance, with one stronger than another. Maintaining good range of movement and symmetry at different joints is important to maintain the best possible function, prevent the development of fixed deformities and prevent pressure problems with the skin.

Our therapists can help design an individualized plan for your child that will encourage muscle strengthening and flexibility.

With time, usually in adulthood, strength becomes more of an issue. Physiotherapists and occupational therapists can recommend assistive devices to help the patient maintain independence. It is important to think proactively about the kind of equipment that will best support independence and participation in daily activities, and plan ahead to provide it in as timely a manner as possible. Additional adaptations may be needed to help with reaching for or lifting objects, getting up stairs, transferring from one place to another (such as from the bed to a chair) and bathing.

Mobility Devices

Mobility devices may increase a person's ability to move, provide support and decrease the risk of injuries. Many people with CMT develop foot deformities that may be corrected with braces. Custom-made shoes or inserts can improve gait and help to evenly distribute the body weight on the foot. Rarely people require extra support for getting around, including canes, walkers or motorized equipment such as a scooter.

Special braces that hold the foot at a 90-degree angle to the leg may also help if muscle weakness causes the foot to drag while walking. If the entire lower leg is severely weakened, braces that extend above the knee and attach to the stronger muscles of the upper leg can provide adequate support.

Surgery

If a foot deformity prevents the foot from being manipulated into proper alignment with a brace, surgery may help. The goal of surgery is to help the foot and leg function as normally as possible, so the patient can walk with minimal difficulty. When foot muscles are too weak to hold the bones in proper position, the foot bones can be surgically fused to provide stability and support.

Managing Complications of Sensory Loss

Combined with the regular abrasions caused by foot deformities, the lack of pain sensitivity makes people with CMT at risk for developing ulcerations — wounds that go unnoticed and become severely infected. People with CMT, and especially those with foot deformities, should check their feet regularly for injuries.

In many people with CMT, sensory loss is associated with dry skin and hair loss in the affected area. In rare cases, sensory loss can include gradual hearing impairment and sometimes deafness. Watching out for these potential problems will enable patients to seek appropriate treatment if necessary.