While rare ocular, distal, and congenital forms of muscular dystrophy exist, the most common varieties of the disease can be classified into three groups: the Duchenne, limb-girdle, and facioscapulohumeral forms. The Duchenne type usually becomes apparent in young boys at about the age of 3 years with difficulty in walking, frequent falling, difficulty in climbing stairs, and a tendency to waddle. Such patients show characteristic difficulty in rising from the floor and often climb up their legs when doing so. Difficulty in walking generally increases progressively, so that by about the age of 10 years most children are unable to walk. Following confinement to a wheelchair at about this age, muscular weak ness causes progressive skeletal deformity and multiple con tractures. Cardiac muscle is almost invariably affected in the later stages, and most boys die from cardiac failure or respiratory infection before the end of the second decade. Hypertrophy of muscles (particularly calves, quadriceps, and deltoids) is a common feature in the early stages, but is later succeeded by progressive wasting. A disorder which is genetically and clinically similar, though of later onset and running a much more benign course, occurs in occasional families and is generally referred to as the benign X-linked Becker type of muscular dystrophy. The rare form of muscular dystrophy closely resembling the Duchenne type which occa sionally afflicts young girls also tends to be less rapidly pro gressive than the classical Duchenne variety. The limb-girdle type is seen equally in the two sexes and is generally manifest first in adolescence or early adult life, though occasionally such cases first develop in middle age. It is characterized by progressive and selective weakness and atrophy of proximal muscles, beginning either in the upper limbs (serratus anterior, pectorals, biceps, brachioradialis are usually affected) or in the lower (hip flexors, quadriceps, and anterior tibials are usually involved early). Sometimes muscular involvement is asymmetrical, and typically the first symptoms are difficulty in raising the arms above the head when the upper limbs are first affected, or difficulty in walking or in climbing stairs when the disease begins in the pelvic girdle. In general, the cases of scapulohumeral onset are somewhat more benign that those in which the pelvic girdle is first involved, but after 10 or 15 years it is almost invariable to find that the disease process spreads from the upper to the lower limbs or vice versa. While much more benign than the Duchenne type, the con dition is slowly progressive, and most patients become severely disabled in about 20 years from the onset and generally die before the normal age. Contractures and skeletal deformity occur late and cardiac involvement is uncommon in this group. The facioscapulohumeral variety is the most benign of all. Facial involvement, with difficulty in closing the eyes, pouting of the lips (the tapir mouth), and inability to whistle or to retain air under pressure in the cheeks is soon apparent, and is accompanied by winging of the scapulae, difficulty in raising the arms above the head, and subsequently by involvement of biceps, brachioradialis, and of other arm and forearm muscles. In the legs the anterior tibial muscles are often first affected in these patients, but eventually a typical waddling gait with involvement of quadriceps, hamstrings, and hip flexors appears, and some patients with this form of the disease show a par ticularly striking accentuation of the lumbar lordosis. This variety also affects the sexes equally, and it is characteristic that within affected families some individuals suffer from the disease in a form so mild that they are virtually unaware that they have it. In these so-called abortive cases it is not uncommon to find that after progressive atrophy of certain selected muscles the disease fails to progress. While occasional cases are severely disabled in early adult life, many survive, though with increasing disability, to a normal life span. Also classified at present with the muscular dystrophies is myotonic dystrophy or dystrophia myotonica. In this con dition progressive weakness and wasting of facial muscles, of the sternomastoids, and of the distal muscles of the limbs is generally accompanied by the phenomenon of myotonia, seen particularly in the tongue, hand, and forearm muscles. Myotonia is the continued active contraction of a muscle persisting after the cessation of voluntary effort or stimulation. Patients with dystrophia myotonica commonly complain of stiffness of the muscles, of difficulty in relaxing the grip, and of other symptoms due to their myotonia rather than to their muscular weakness, at least in the early stages of the disease. Many patients also show frontal baldness in the male, cataracts, gonadal atrophy, and mental backwardness or dementia.
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Dec 31, 1998
Pamela M Sourgen + 1
