Dermatomyositis is an inflammatory condition characterized by muscle weakness and a skin rash. Although the disease primarily affects the muscles and skin, it is a systemic condition and can also involve the lungs, joints, esophagus and sometimes the heart.
The exact cause of dermatomyositis is not clearly understood, although the condition shares many similarities with autoimmune disorders, where the immune system attacks the body’s own tissues. One theory regarding the underlying mechanism of the disease is that autoantibodies are produced that target the endothelium of capillaries in the muscles, preventing their supply of oxygenated and nutrient-rich blood.
The skin rash seen in dermatomyositis usually develops on the face, eyelids and around the knuckles, elbows, knees, back and chest. The rash is dusky red or violet in colour, sometimes with a bluish discoloration.
The muscle weakness is progressive and affects the muscles closest to the trunk such as those found in the upper arms, shoulders and neck as well as those in the thighs and hips. The weakness that occurs is symmetrical in nature, affecting muscles on both the left and right sides of the body.
Some examples of other symptoms that may occur include:
Muscle pain or tenderness
Calcium deposits under the skin, particularly in children
In adults, the age of onset is usually between the late 40s and early 60s and in children symptoms usually begin between 5 and 15 years of age. The condition is more common among females than men.
Although there is no cure for dermatomyositis, a range of treatments are available that can help to improve the skin and the function of muscles. The earlier the treatment is started, the more effective it is.
The most common first-line approach to treatment involves the use of corticosteroids to suppress the immune system and reduce muscle inflammation. A secondary immunosuppressive agent may be added to the treatment regimen if the first corticosteroid is not effective on its own.
In severe cases that do not respond to these initial therapies, rituximab or a tumor necrosis factor inhibitor may be prescribed as a third-line approach as these drugs are currently being investigated for their effects in dermatomyositis.
Other treatment options include the use of over-the-counter pain relief medication, physical therapy and surgery to remove painful calcium deposits.
Reviewed by Sally Robertson, BSc