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A 45-year-old woman presents to her physician with an 8-month history of gradually increasing limb weakness. She first noticed difficulty climbing stairs, then problems rising from chairs, walking more than half a block, and, finally, lifting her arms above shoulder level. Aside from some difficulty swallowing, she has no ocular, bulbar, or sphincter problems and no sensory complaints. Family history is negative for neurological disease. Examination reveals significant proximal limb and neck muscle weakness with minimal atrophy, normal sensory findings, and intact deep tendon reflexes. The most likely diagnosis in this patient is
A) Polymyositis
B) Cervical myelopathy
C) Myasthenia gravis
D) Mononeuropathy multiplex
E) Limb-girdle muscular dystrophy
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Polymyositis is an acquired myopathy characterized by subacute symmetrical weakness of proximal limb and trunk muscles that progresses over several weeks or months. When a characteristic skin rash occurs, the disease is known as dermatomyositis. In addition to progressive proximal limb weakness, the patient often presents with dysphagia and neck muscle weakness. Up to half of cases with polymyositis-dermatomyositis may have, in addition, features of connective tissue diseases (rheumatoid arthritis, lupus erythematosus, scleroderma, Sjögren syndrome). Laboratory findings include an elevated serum CK level, an EMG showing myopathic potentials with fibrillations, and a muscle biopsy showing necrotic muscle fibers and inflammatory infiltrates. Polymyositis is clinically distinguished from the muscular dystrophies by its less prolonged course and lack of family history. It is distinguished from myasthenia gravis by its lack of ocular muscle involvement, absence of variability in strength over hours or days, and lack of response to cholinesterase inhibitor drugs.
