Diagnosis of dermatomyositis and polymyositis: a study of 102 cases

Patients with dermatomyositis (DM) or polymyositis (PM) were studied retrospectively. The patients were divided into four groups: definite PM 24, probable PM 19, definite DM 34 and mild-early DM 25 cases. PM patients complained more often proximal muscle weakness [p <0.01]. DM patients complained more arthralgia [p <0.05], dysphagia [p <0.03] and weight loss [p <0.04]. Five patients had a malignant neoplasm and 9 had other connective-tissue disease. DM presented higher ESR than PM [p <0.002]. PM presented more significant increase in creatine kinase (CK) [p <0.02] and in alanine aminotransferase (ALT) [p <0.001] levels. Electromyography showed myopathic pattern in 76%. Muscle biopsy was the definitive test. Perifascicular atrophy was more frequent in definite DM than in mild-early DM group [p <0.03].

A small association with connective-tissue diseases and neoplasms was found. DM and PM are clinically different. DM presents systemic involvement affecting the skin, developing more severe arthralgia, dysphagia and weight loss and presenting higher values of ESR. PM presents a restricted and more significant involvement of muscles generating more weakness complaints and higher levels of serum muscle enzymes.