Group IV: Childhood Polymyositis And Dermatomyositis Associated With Vasculitis
This group comprises about 8 to 20 percent of all cases of myositis in various series. Inflammatory myopathy in childhood is frequently associated with skin involvement and clinical or histologic evidence of vasculitis in skin, muscles, gastrointestinal tract, and other organs. Degeneration and loss of capillaries in a perifascicular distribution occur in the skeletal muscles; often necrotizing lesions of the skin, and ischemic infarction of kidneys, gastrointestinal tract, and rarely brain may be seen. Consequently, some authors have reported mortality rates of up to one-third in childhood dermatomyositis, though most have found that the prognosis is better than in adult dermatomyositis-polymyositis. Based upon current data, it is unclear whether or not all cases of childhood myositis should be included in group IV. Subcutaneous calcification is frequently present in childhood dermatomyositis.
Group V: Polymyositis Or Dermatomyositis With An Associated Connective Tissue Disorder
This “overlap group” of myositis comprises about one-fifth of all cases that occur in association with several connective tissue diseases. Progressive systemic sclerosis, rheumatoid arthritis, mixed connective tissue disease (the rheumatologic overlap disorder), and lupus erythematosus are the most common associated conditions; polyarteritis nodosa and rheumatic fever are more rarely associated. Criteria for placement in the “overlap group” combine the demonstration of the appropriate clinical and laboratory abnormalities required for the diagnosis of the connective tissue disorder together with clinical and laboratory evidence of myositis. The diagnosis of myositis is often difficult in patients with a connective tissue disorder producing arthritis with secondary (disuse) muscle weakness with type II fiber atrophy. Moreover, perivascular inflammatory foci are common in muscle in connective tissue disorders. Demonstration of increased serum creatine kinase (CK), >electromyography (EMG), and muscle biopsy are often required to make this diagnosis. Though patients in this overlap group usually respond to glucocorticoid therapy, the prognosis for recovery of function is poorer than in pure dermatomyositis-polymyositis. Dysphagia in group V patients with progressive systemic sclerosis is often due to involvement of the smooth muscle of the distal third of the esophagus.
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