Characteristics and Symptoms of CMTAlthough there are many different genetic causes of Charcot–Marie–Tooth Disorder, all types tend to have remarkably similar symptoms. What follows is a general description of these symptoms. Individual patients may not experience all of these symptoms, and the severity of the symptoms may vary greatly from one person to the next.
A high arched foot is usually one of the first signs of this disorder, although in some instances extremely flat feet are also typical of Charcot–Marie–Tooth Disorder. As the disease progresses, structural foot deformities take place. The patient may develop a pes cavus (high–arched) foot and hammer toes.
The progressive muscle wasting of Charcot–Marie–Tooth Disorder also leads to problems with walking, running, and balance. Ankle weakness and sprains are common, and many patients develop foot drop. To avoid tripping, patients with foot drop raise their knees unusually high, resulting in the high “steppage” gait associated with Charcot–Marie–Tooth Disorder. In some patients, muscle weakness may also occur in the upper legs.
Later in the course of the disease, hand function may become affected. Progressive atrophy of the thenar muscle and the small muscles in the hand results in weakening or loss of the opposable pinch, and tasks requiring manual dexterity become difficult. Patients have problems writing, holding utensils, buttoning clothing, grasping zipper pulls and turning doorknobs. Many people benefit from occupational therapy which helps people accomplish the tasks of daily living with the use of assistive devices.
The loss of nerve function is often accompanied by tingling and burning sensations in the hands and feet. This usually causes little more than mild discomfort, but some people experience severe neuropathic pain and require medication to control it.
At the same time, loss of nerve function in the extremities can also result in sensory loss. The sense of touch is diminished, as is the ability to perceive changes in temperature. Sensory loss notwithstanding, many patients are extremely sensitive to the cold or even to temperatures a few degrees lower than normal. The “stocking–glove” pattern of atrophy results in the loss of insulating muscle mass, which, combined with reduced muscular activity and circulation, can leave patients with chronically cold hands and feet. Impairment of the normal circulatory process can also result in swelling (edema) of the feet and ankles.
In many patients, deep–tendon reflexes, such as the knee jerk reaction, are lost. This does not cause any particular problem but is often noted on physical exams. Some people with Charcot–Marie–Tooth Disorder also have tremor (usually of the hands) and the combination of tremor and Charcot–Marie–Tooth Disorder is sometimes referred to as Roussy–Levy Syndrome.
Weakness of the respiratory muscles is in rare in people with Charcot–Marie–Tooth Disorder, but when present, it can cause life–threatening problems. If shortness of breath is an issue, a patient should be checked by a respiratory specialist to see if the use of a ventilator is recommended.
Another problem related to Charcot–Marie–Tooth Disorder can be scoliosis or mild curvature of the spine. This often occurs in puberty and tends to be most common in people with early onset of gait abnormalities. Hip dysplasia also affects a small number of CMT patients at an early age.
As noted, the severity of symptoms can vary greatly from patient to patient, even within the same family. A child may or may not be more severely disabled than his/her parent. Some family members may experience significant impairment and require bracing while others have no noticeable symptoms but are found to have CMT upon examination by EMG or nerve conduction studies.
Diagnosis of Charcot–Marie–Tooth DisorderCharcot–Marie–Tooth Disorder is usually first noticed when someone develops lower leg weakness and foot deformities such as foot drop, hammer toes and high arches, but that alone will not lead to diagnosis. Sensory loss is often identified when the doctor tests for deep tendon reflexes, such as the knee jerk, which are reduced or absent in CMT patients.
Since Charcot–Marie–Tooth Disorder is strongly hereditary, it is important to tell the doctor about any other family members with CMT–like symptoms. Lack of family history does not rule out CMT, but it will cause the doctor to look further to rule out other causes of neuropathy such as diabetes or exposure to certain chemicals or drugs.
Further testing may be electrodiagnostic, genetic, or both. Electrodiagnostic testing used to diagnose CMT usually includes a nerve conduction velocity test (NCV), which measures the strength and speed of electrical signals moving down the peripheral nerves. Delayed responses are a sign of demyelination (type 1) and small responses are a sign of axonopathy (type 2). An electromyogram (EMG) is also used to measure the electrical signal’s strength in the muscles of the arms or legs.
Genetic tests, done by drawing blood, are available to test for many, but not all, of the common chromosomal defects causing Charcot–Marie–Tooth Disorder. A positive genetic test can provide definitive diagnosis and provide useful information for family planning. However, a negative result does not rule out CMT since some forms cannot yet be tested by DNA sampling. Currently, 18 types can be identified by DNA testing: 1A, 1B, 1C, 1D, 1E, 1F, 1X, 2A, 2E, 2I, 2J, 2K, 4A, 4E, 4F, HNPP, CHN, and DSN.