Congenital Myasthenic Syndromes

Diagnosis

Symptoms for congenital myasthenic syndromes (CMS) vary widely. They depend on the patient's type of congenital myasthenic syndrome and the age when the disorder begins — syndromes that don't develop until later in childhood or in adulthood usually have milder symptoms than those that begin in infancy. Because many symptoms are shared with myasthenia gravis and other muscular diseases, CMS can be difficult to recognize and diagnose.

Diagnostic tests necessary to determine the presence of CMS are available at all Mayo locations. Once a CMS is identified, specialized testing to determine the precise type can be done by special arrangement only at Mayo Clinic in Minnesota. It requires that the patient come to the laboratory for the testing.

Some distinctions that doctors look for include: onset at or near birth (as congenital implies); the presence of CMS in other family members (though parents or siblings can carry the defective gene without having symptoms); and an absence of acetylcholine (ACh) receptor antibodies which are present in most (but not all) forms of myasthenia gravis — but not in CMS.

In addition to these clues, doctors will look at a patient's medical history, perform a physical and neurologic evaluation and use various tests.

Tests to determine the particular type of CMS can include:

• An electromyogram (EMG) to record the electrical activity of the muscles
• Biopsy of muscle tissue to observe nerve and muscle cell behavior in response to different stimuli
• Genetic testing to verify a mutation