Dermatomyositis is one of a group of inflammatory muscle diseases of which it is a sub type. The disease, which has a subacute (somewhat short and relatively severe) onset, can affect both children and adults. Females are more often affected than males.
Dermatomyositis is characterised by a rash accompanying, or more often, preceding muscle weakness. The rashes include purple discoloration around the eyes, a patchy reddish rash around the neck, shoulders and upper chest and a scaly rash over the elbows, knees, knuckles and back.
Some patients may also develop hardened bumps of calcium deposits under the skin.
Muscle weakness usually affects those muscles that are closest to the trunk of the body (proximal). Patients characteristically have difficulty rising from a sitting position, climbing stairs, lifting objects or reaching overhead, for example combing hair or packing shelves. Rarely, distal muscles (those not close to the trunk of the body) may be affected.
Trouble with swallowing (dysphagia) may occur. Occasionally, the muscles ache and are tender to the touch. Patients may also feel fatigue and discomfort and have weight loss or a low-grade fever.
Dermatomyositis is diagnosed from the clinical setting of rash and weakness, but muscle tests are also important. These include measuring the blood for CPK muscle enzyme, as well as electrical tests, called EMG, on the muscles, done by a neurologist. A biopsy of affected muscle is then done by a general surgeon, and tissue sent to a pathologist. Inflammation of the muscle tissue is the typical finding.
Dermatomyositis usually responds to therapy. The disease is more severe and resistant to therapy in patients with heart or lung involvement. It may occasionally be associated with an underlying cancer, especially in those patients with an elderly onset. Early diagnosis of and treatment for the cancer where present, may result in disease remission. The patients should therefore have a good general physical examination and a chest X-ray, ultrasound of the abdomen and scans, depending on suspicious symptoms or findings.
Treatment for dermatomyositis consists of prednisone (a form of cortisone). For patients in whom prednisone is not effective, other immunosuppressants such as azathioprine, cyclosporin and methotrexate may be prescribed. A medication called intravenous immunoglobulin has also been used in the treatment of some patients.
Physical therapy is usually recommended to preserve muscle function and avoid muscle atrophy.
Previously reviewed by Dr David Gotlieb, rheumatologist
Reviewed by the Arthritis Foundation, September 2011