Patients older than age 40

13 November of 2008

Patients older than age 40, particularly those with dermatomyositis, should be followed closely for the possibility of malignant disease. If a malignant lesion is found, it should be treated, since the muscle weakness may disappear if the neoplasm is eradicated. However, a response to glucocorticoids can usually be obtained even in patients with dermatomyositis-polymyositis associated with a malignancy. (more…)


11 October of 2008

Glucocorticoids in high dosage is the accepted treatment for severe dermatomyositis-polymyositis, though there is no controlled trial to prove its effectiveness. Prednisone is generally started at a dose of 1 to 2 mg/kg body weight per day (60 to 100 mg/d for adults). Improvement may begin within 1 to 4 weeks, though in some patients treatment may need to be continued for 3 months before improvement occurs. When improvement is noted, the daily dose may be reduced by 5 mg every 4 weeks. Repeated manual muscle testing and serum CK determinations should be performed to ensure that the myositis does not relapse. At about 40 mg/d, the schedule is changed gradually to 80 mg every other day in order to reduce the incidence of glucocorticoid side effects. There is some evidence that the use of alternate-day glucocorticoids from the outset may be effective, particularly in patients with milder disease.


Skeletal Muscle Pathology

09 October of 2008

The principal changes in muscle consist of infiltrates of inflammatory cells (lymphocytes, macrophages, plasma cells, and rare eosinophils and neutrophils) and destruction of muscle fibers with a phagocytic reaction. Perivascular (usually perivenular) inflammatory cell infiltration is the hallmark of polymyositis. Interstitial inflammatory cell infiltration is also a prominent feature of the disease, but lesser degrees of it may be seen in other conditions as a secondary reaction (e.g., in facioscapulohumeral and Becker’s muscular dystrophy). (more…)

Laboratory Findings

02 October of 2008

In all forms of polymyositis there may be elevated serum levels of the enzymes present in skeletal muscle, such as, aldolase, serum glutamic oxaloacetic transaminase, lactic acid dehydrogenase, and serum glutamic pyruvate transaminase. The degree of elevation decreases from the first to the last in this series of enzymes, and the pattern is the reverse of that seen in liver disease. The erythrocyte sedimentation rate is elevated in about two-thirds of cases. Tests for circulating rheumatoid factor are positive in less than one-half and for antinuclear antibodies in about three-quarters of the cases. Most other hematologic indexes are normal. Several autoantibodies seem to be associated with clinically distinct groups of patients. Anti-Jo-1 antibodies are more common in polymyositis, especially in patients with interstitial lung disease, and anti-nRNP antibodies are often associated with polymyositis seen in lupus erythematosus. (more…)

Childhood Polymyositis

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. (more…)

Clinical Manifestations

01 October of 2008


Current estimates of the annual incidence of the inflammatory myopathies are approximately five cases per million population. These estimates are probably low, however; the true incidence may be as high as two to three per hundred thousand.

Clinical Manifestations

Group I: Primary Idiopathic Polymyositis

This group comprises about one-third of all cases of inflammatory myopathy. It is usually insidiously progressive over weeks, months, or even years. Rarely the disease is acute, producing severe muscle weakness in a matter of days or even rhabdomyolysis. The disease may develop at any age. Affected females outnumber males 2:1.



04 May of 2008

Dermatomyositis and polymyositis are autoimmune disorders in which the skeletal muscle is damaged by an inflammatory process dominated by lymphocytic infiltration. The term polymyositis is applied when the condition spares the skin, and the term dermatomyositis when polymyositis is associated with a characteristic skin rash. One-third of cases are associated with various connective tissue disorders, such as rheumatoid arthritis, lupus erythematosus, mixed connective tissue disorder, and progressive systemic sclerosis, and one-tenth with a malignancy. Inclusion body myositis is a distinct clinicopathologic entity characterized by the presence of vacuolated inclusions containing tubulofilaments in muscle.