Muscle Diseases - The myotonias
This is a group of muscle diseases characterized by myotonia , a continuation of muscle contraction after the patient has voluntarily tried to relax that contraction. It is best observed in the patient who holds an object firmly in his hand and then tries to release his grasp suddenly, only to realize that he cannot let go quickly. There are two major members of this group of diseases and several other less common variants.
As in the case of muscular dystrophy, there is no specific treatment for myotonia. Some drugs, such as quinine, have limited value in decreasing the abnormally prolonged muscular contractions, but as yet no treatment has been completely effective.
This condition is usually present at birth, but is recognized later in the first or second decade of life when the child complains of stiffness or when clumsiness is noted. A child with this condition appears very muscular and has been called the “infant Hercules.” The unusual muscular development persists throughout life, but the myotonia tends to improve with age.
The other major variety of myotonia, myotonic dystrophy , is a disease in which many organ systems in addition to muscle are involved. Both males and females are affected equally, and the onset may occur at any time from birth to the fifth decade. It is not unusual for a patient to recognize some clumsiness, but he may not be aware that he has a muscle disease. The myotonia may range from mild to severe. There is a striking similarity in the physical appearance of patients with myotonic dystrophy, the features of which include frontal baldness in the male, wasting and weakness of the temporal muscles (that control closing the jaws), muscles of the forearm, hands, and anterior leg muscles. Other physical abnormalities include cataracts in about 90 percent of the patients, small testicles, and abnormality of the heart muscle. Thickening and other bony abnormalities have been seen in the skull radiogram and, with time, many patients become demented.