Hereditary motor sensory neuropathy
Hereditary motor sensory neuropathy is the term used to describe an inherited disease of the peripheral nerves that is usually characterized by a weakness and numbness of the extremities that affects the legs in particular. In this condition the muscles of the hands and feet become progressively weaker since they do not receive normally-conducted nerve impulses. Symptoms can vary greatly and may include pain, numbness, and difficulties with balance when standing. Hereditary motor sensory neuropathy is sometimes referred to as Charcot-Marie-Tooth disease.
Definition & Facts
As its name implies, hereditary motor sensory neuropathy is an inherited condition that affects both the motor (movement) and sensory (feeling) nerves. Although it is present at birth, symptoms of the condition typically do not appear until childhood. However in milder cases, symptoms may not appear until early adulthood with a few cases not being diagnosed until the individual is in his or her late 30s.
The condition is not generally considered fatal since most of those with the condition have normal life span, albeit with at least some walking difficulties, and most deaths occur as a result of other illnesses or as a complication of injury.
In the United States, it is estimated that there are about 150,000 active cases with a nearly even male to female ratio. In the past it was felt that hereditary motor sensory neuropathy was transmitted only through inheritance, but modern DNA technology suggests that there are infrequent cases in which neither parent possesses the defective gene or genes responsible for this condition.
Hereditary motor sensory neuropathy is an (almost always) inherited condition that is the result of a defect in the gene (or genes) responsible for producing the myelin sheath or nerve axon. This impairs the ability of the muscles to efficiently send and receive nerve impulses.
Symptoms & Complaints
Hereditary motor sensory neuropathy is caused by mutations in the genes that produce proteins involved in the nerves of the legs, feet, and hands. There are many different genetic mutations that can occur that cause this condition. These genes include the following: PMP22, MPZ, LITAF, EGR2, NEFL, MFN2, RAB7A, LMNA, BSCL2, GARS, NEFL, MPZ, GDAP1, HSPB8, and DNM2.
This condition can be inherited through autosomal recessive inheritance, autosomal dominant inheritance, and X-linked dominant inheritance. Occasionally this condition appears in those with no family history of the disease and arises from spontaneous mutations.
Diagnosis & Tests
The initial diagnosis of hereditary motor sensory neuropathy derives from the patient’s medical history of progressive weakness involving first the arms and hands and then the lower extremities. The next step in establishing a diagnosis is a series of nerve conduction studies (which includes a nerve conduction velocity test) and electromyograms (EMG) which measures the electrical activity of muscles.
If the EMG demonstrates abnormal conduction through the motor and sensory nerves of the extremities, the initial diagnostic impression is confirmed by a nerve biopsy. The biopsy is carried out under local anesthesia and involves removal of a small section of nerve tissue for examination by a pathologist.
In some cases, depending on both the physical examination and the biopsy findings, additional DNA testing will be obtained in order to exclude the rare autoimmune conditions that may mimic or even contribute to the progression of hereditary motor sensory neuropathy.
Treatment & Therapy
Since those with hereditary motor sensory neuropathy will generally have a normal lifespan, treatment and therapy will be directed at improving quality of life issues and management of secondary conditions. Unfortunately, there is no currently accepted treatment that will halt or reverse the progression of the disease.
Treatment is thus directed toward maintaining mobility and management of other conditions that are secondary to the loss of motor and sensory nerve function. The foot problems usually associated with the condition, such as hammer toes and foot drop, are managed in consultation with an orthopedic surgeon or podiatrist.
In severe cases of this condition, scoliosis, particularly of the thoracic vertebrae and lumbar vertebrae may develop. This condition, if it develops, should be managed by an orthopedist with extensive training and experience in the management of spinal pathologies.
Physical therapy is a valuable modality in this condition as stretching and balance exercises can make a major contribution to quality of life. Likewise, occupational therapy can be invaluable in helping with necessary adaptations that will need to be made in activities of daily living.
Since many suffering from this condition experience chronic moderate to severe pain, nerve blocks in combination with oral analgesics are frequently necessary. Close monitoring of other disease processes that develop secondarily to, or independently of, hereditary motor sensory neuropathy is necessary.
Doctors must also be cautious in prescribing medication due to the effects of medications and anesthetics such as thiopentol on those with this condition. Also, some chemotherapy medications may cause a sudden increase in the degree of peripheral neuropathy and may accelerate disease progression.
Prevention & Prophylaxis