In storage diseases, enzyme deficiencies cause impaired purine, glycogen, or lipid utilization, resulting in symptoms ranging from mild muscle cramps to severe pain and elevated CK levels following exercise. The key difference between inflammatory myopathies and storage diseases is that weakness is present at initiation of an activity in myositis, whereas storage diseases require some degree of exertion before symptoms develop. The muscles affected in the storage diseases are primarily proximal, whereas weakness is generally distal and can be asymmetric in inclusion body myositis. Also, weakness in inclusion body myositis is insidious, progressing over a period of years, and is accompanied by muscle wasting. In muscle weaknesses, the major point of differential diagnosis is determining whether the disease is neuropathic or myopathic in origin. When accompanied by neurologic abnormalities, the presence of fasciculations is suggestive of destruction of the motor neuron or its axon. Benign fasciculations can occur in healthy persons, especially in the calves and hands. Duchennesmuscular dystrophy is an X-linked recessive disorder that affects males almost exclusively. Onset usually occurs by 5 years with progressive muscle weakness of the girdle muscles; ambulation is severely affected by age 12 years.
- Storage diseases.
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Seminars in Medical Practice
Hospital Physician Board Review Manuals
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