[Differential diagnosis of polymyositis. Case report]

Polymyositis is a connective tissue disease of unknown etiology. Autoimmune processes in genetically predisposed individuals play an important role in the pathogenesis of this disease. It is suspected that environmental factors operate in the initiation of the autoimmune response. The differential diagnosis of polymyositis should take into consideration various disorders presenting with muscular lesions or weakness.

Our 33-year-old female was referred in 2010 to the Department of Rheumatology, Rehabilitation, and Internal Medicine, Poznań University of Medical Sciences, with suspected polymyositis. She reported symptoms of upper airway infection in December 2009 with muscle tenderness in the pelvic and pectoral girdles and the dorsum. An antibiotic was administered but aggravation of symptoms was noted instead. She was hospitalized with muscle weakness and elevated CPK (16300 U/L), LDH (2322 IU/L), aminotransferases, ESR, and CRP. Other causes of muscular lesions or weakness were ruled out. Polymyositis was tentatively diagnosed by a rheumatologist and the patient was started on non-steroid anti-inflammatory agents. After one week in hospital, improvement in the general condition and normalization of laboratory tests were noted (CPK and LDH activities declined). The patient was referred to our Department for further investigation and treatment. Basing on the anamnesis, physical examination, and laboratory findings, and taking into consideration that the patient quickly improved and the tests normalized without glucocorticoids, we decided against the diagnosis of polymyositis.

Our differential diagnosis attributed the symptoms of inflammatory muscle disease to an infectious or chemical factor or to a malignancy as the primary condition.