The most common signs and symptoms of dermatomyositis include:

• Skin changes. A violet-colored or dusky red rash develops, most commonly on your face and eyelids and on knuckles, elbows, knees, chest and back. The rash, which can be itchy and painful, is often the first sign of dermatomyositis.
• Muscle weakness. Progressive muscle weakness involves the muscles closest to the trunk, such as those in your hips, thighs, shoulders, upper arms and neck. The weakness affects both the left and right sides of your body, and tends to gradually worsen.

The cause of dermatomyositis is unknown, but the disease has much in common with autoimmune disorders, in which your immune system mistakenly attacks your body tissues.

Small blood vessels in muscular tissue are particularly affected in dermatomyositis. Inflammatory cells surround the blood vessels and eventually lead to destruction of muscle fibers.

Possible complications of dermatomyositis include:

• Difficulty swallowing. If the muscles in your esophagus are affected, you can have problems swallowing (dysphagia), which can cause weight loss and malnutrition.
• Aspiration pneumonia. Difficulty swallowing can also cause you to breathe food or liquids, including saliva, into your lungs (aspiration).
• Breathing problems. If the condition affects your chest muscles, you might have breathing problems, such as shortness of breath.
• Calcium deposits. These can occur in your muscles, skin and connective tissues (calcinosis) as the disease progresses. These deposits are more common in children with dermatomyositis and develop earlier in the course of the disease.