Symptoms of myositis can include muscle weakness, muscle pain and muscle tenderness. Other symptoms vary, depending on the specific cause of myositis:
Idiopathic inflammatory myopathies. These conditions typically cause painless muscle weakness that develops slowly over weeks, months or years. Although up to 40% of people with 1 of these conditions have muscle pain, the weakness is usually worse than the pain.
In polymyositis and dermatomyositis, weakness usually affects the muscles near the center of the body (called proximal muscles), including the muscles of the neck, shoulders and hips. Some patients also have difficulty swallowing.
In dermatomyositis, skin symptoms accompany muscle problems. These can include purple discoloration of the eyelids, a red rash on the face and neck, or scaly patches, usually on the knuckles.
In inclusion body myositis, weakness typically starts in the upper legs and later affects the upper arms and muscles farther away from the center of the body (called distal muscles), including muscles of the hand and wrist and lower legs. Muscle wasting (atrophy) is often prominent. Up to one-half of these patients have trouble swallowing.
Infectious myositis. When infectious myositis is caused by the flu, symptoms include not only muscle aches and muscle weakness, but also high fever, chills, sore throat, cough, fatigue and runny nose. When caused by trichinosis, symptoms in the early stages include diarrhea and vomiting. Later, as the parasites invade the muscles, symptoms can include fever, eye redness with swelling in the lids and muscle pain. Patients with pyomyositis usually have a fever, and the abscessed muscle is painful, tender and slightly swollen. Skin over the muscle may be red and hot.
Benign acute myositis. A child suddenly has trouble walking and complains of severe leg pain. This pain is often worst in the calf muscles. In most cases, the child also has a history of recent fever, runny nose, sore throat and other upper respiratory symptoms.
Myositis ossificans. A lump appears in the affected muscle, and this lump may hurt when you press it. These symptoms usually begin several weeks after a muscle injury, especially a bruise.
Drug-induced myositis. Symptoms include muscle soreness, pain and weakness. These symptoms usually begin soon after a person starts taking a new drug or a combination of drugs. Myositis is more common when a person is taking a combination of lipid-lowering medications, such as gemfibrozil (Lopid) and lovastatin (Mevacor), than when a single medication is used.