The clinical and pathologic picture of dysimmune or idiopathic myopathies and collagen-vascular diseases (connective tissue diseases) have many common features. Hence arose a question, whether and to what extent the bioptical examination may contribute to the correct diagnosis and differential diagnosis of these groups of diseases. The term dysimmune myopathies covers several forms of polymyositis, dermatomysitis and inclusion body myositis. Nowadays, polymyositis is considered a T cell mediated immune myositis, dermatomyositis a humoral mediated immune vascular lesion, while inclusion body myositis a degenerative (metabolic, infective?) lesion with a secondary inflammation. A characteristic feature of histopathological picture of myositis is cellular reaction, the presence of an inflammatory infiltration of the endo- and/or perimysium. Besides, the presence o MAC in the wall of small blood vessels, the presence of amyloid in the inclusions bodies and expression of HLA class I in the sarcolemma (not specific for the inflammatory myopathies) may be valuable diagnostic aid. Skeletal muscle may also be affected by inflammatory or dystrophic alterations in conditions in which it is not the primary target of the attack, particularly in collagen vascular diseases. Pathologic alterations of the skeletal muscle may be hardly distinguishable from idiopathic myositis. Differential diagnosis may be facilitated by the results of clinical, biochemical and immunological examination of the patient. In order to contribute to the diagnosis effectively, the biopsy must be taken from the typically affected muscle and/or from a typical lesion in the skin.

        Key words: dysimmune myopathies, connective tissue disease, biopsy, immunohistochemistry