What Is Dermatomyositis?
Dermatomyositis is part of a group of rare diseases called the inflammatory myopathies that involve chronic (long-standing) muscle inflammation, muscle weakness, and in some cases, muscle pain. Myopathy is a general term used to describe a number of conditions affecting the muscles. All myopathies can cause muscle weakness. Both children and adults can be affected.
Dermatomyositis is characterized by a skin rash that precedes or accompanies progressive muscle weakness. The rash appears patchy, with purple or red discolorations, and characteristically develops on the eyelids and on muscles used to extend or straighten joints, including knuckles, elbows, knees, and toes. Red rashes also may occur on the:
- Face
- Neck
- Shoulders
- Upper chest
- Back, and other locations
There may be swelling in the affected areas. The rash sometimes occurs without obvious muscle involvement and often becomes more evident with sun exposure.
Adults with dermatomyositis may experience weight loss or a low-grade fever, have inflamed lungs, and be sensitive to light. Children and adults with dermatomyositis may develop calcium deposits, which appear as hard bumps under the skin or in the muscle (calcinosis). Calcinosis most often occurs one to three years after disease onset but may occur many years later. These deposits are seen more often in childhood dermatomyositis than in dermatomyositis that begins in adulthood.
In some cases of dermatomyositis, the distal muscles (muscles in the forearms and around the ankles and wrists) may be affected as the disease progresses. The disorder also may be associated with collagen-vascular or autoimmune diseases such as lupus (in which the body's immune response system that normally defends against infection and disease attacks its own muscle fibers, blood vessels, connective tissue, organs, or joints).
Source: National Institute of Neurological Disorders and Stroke (NINDS)