Muscle weakness can progress for several weeks or months. However, for the clinical detection of muscle weakness, a minimum of 50% of the muscle fibers must be damaged (thus, the presence of muscle lethargy indicates progression of the myositis). Affected persons may found it difficult to lift their arms above shoulder level, to walk up the stairs, to rise from sitting.

Due to the unusual impotence of the girdle of shoulder and the pelvic muscles, patients may be riveted to a wheelchair or bed. The defeat of the muscles of the larynx and the upper parts of the esophagus leads to a violation of swallowing and regurgitation. The muscles of the lower and upper limbs and face are usually not affected. Skin eruptions usually have a dark color and erythematous character. Periorbital swelling of purple color is also a characteristic. Skin eruptions may slightly rise above the skin surface and be smooth or covered with scales.

Rashes are located on the forehead, lower legs, neck, shoulders, forearms, chest, back, eyebrows, knee areas, medial malleolus, back surfaces of joints between phalanges, lateral side (Gottron’s symptom). Hyperemia of the base or periphery of the nails is also possible. On the skin of the lateral surface of the fingers, it is possible to develop desquamate dermatitis accompanied by the appearance of cracks. Possible formation of subcutaneous calcifications, especially in children.