The congenital myopathies are a group of rare muscle disorders. They are not muscular dystrophies, although they are among the neuromuscular disorders covered by the Muscular Dystrophy Association. They are generally characterized by benign, non- or slowly progressive muscle weakness present at birth. The weakness is generally proximal, but may also be distal and affect the facial muscles. Intelligence is almost always unaffected. However, the myopathies vary greatly both in presentation and in severity. Not only do they vary between the types, there are variations within each type. The conditions are sometimes obvious at birth, but at other times not until early childhood or later. Some people with myopathies use wheelchairs, others walk with the assistance of braces or other aids, and some appear to have no difficulties with mobility. Yet all have the same problems with their muscles. Most children have delayed motor milestones (crawling, walking, etc.), but the severity of the delays vary. Children generally progress thoughout childhood, but the course of the disorder is variable in adulthood. Some people have no apparent problems, while others have decreasing mobility. Some also have muscle pain. Generally, those least affected as children have the fewest problems as adults, but not always. If it seems I'm qualifying each statement, it's because that's the nature of myopathies. There are general trends, but with exceptions to almost all.
There are variants of two types of myopathies which present in a severe infantile form. These are mentioned on the types page. Most of my information is related to the less severe forms. Mitochondrial myopathies are another group of specific disorders causing muscle weakness, but are a different classification from the congenital myopathies and not part of my discussion.
Myopathies may present in infancy, as a floppy baby. There may also be breech presentation with or without congenital hip dislocation or dysplasia. In other cases, there may not be a diagnosis until an older child is consistently late in meeting motor milestones, or has motor difficulties in conjunction with speech problems (due to facial weakness). Some people are diagnosed as adults, after years of feeling something is wrong or after others in their family have had problems and received a diagnosis. Some symptoms of myopathies, other than delayed motor milestones, are an inability to run and jump, lordosis, difficulty in rising from the floor--use of the Gower's maneuver, decreased muscle bulk, hypotonia, inability to completely shut the eyes, hypermobile joints, dysmorphic features, and decreased stamina. All people do not show all symptoms--the symptoms shown by any individual will depend on the the severity of the disorder, the muscles affected, and the specific myopathy.
A muscle biopsy is the only way to definitively diagnose a myopathy. Several other tests, generally performed by neuromuscular specialists, can indicate fairly reliably that a myopathy should be considered. In fact, most patients where a myopathy is suspected should be seen by a neuromuscular specialist (and children by a pediatric neuromuscular specialist) as regular neurologists may not have the same familiarity with these very rare disorders. A CK enzyme test can rule out the muscular dystrophies, and the level may indicate a myopathy. A Nerve Conduction Study (NCV) can rule out the neuropathies. An Electromyography, or EMG, will give a neuromuscular specialist a good indication that a myopathy is involved. Most people have these tests before a muscle biopsy. All patients do not choose to have a biopsy, as it is an invasive procedure, but it is the only way both to definitively diagnose a myopathy, and to pinpoint the specific myopathy.
There may be some fairly serious complications associated with the myopathies. Malignant Hyperthermia, a potentially fatal reaction to anethestics, is one. There may also be heart and respiratory involvement. All individuals do not have this involvement, but doctors monitor all persons with myopathies just in case. In most cases, life span is not affected by these disorders.
The congenital myopathies are generally benign, non-progressive disorders with a varying amount of muscle weakness. There are more serious complications, and more severe presentations, and doctors monitor these conditions as necessary. It is important to get a good diagnosis, as there are other conditions, such as Spinal Muscular Atrophy and the muscular dystrophies, which often present in a similar manner. Physical, speech and occupational therapy are often helpful. Good medical care and supportive services help people with myopathies to live full, mobile, productive lives.
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