Dermatomyositis tends to develop slowly over months or years. However, it can occur suddenly in some cases. Onset in children is more likely to be acute, whereas symptoms may come on more gradually in adults. In addition, there may be periods of remission, when symptoms are less prevalent.

Dermatomyositis is characterized by progressive muscle weakness that begins with muscles closest to and within the trunk of the body, such as neck, hip, back and shoulder muscles. In some patients, muscles further away from the trunk also become weakened. Over time, the condition makes every day activities, such as climbing stairs and lifting objects, extremely difficult.

Symptoms tend to affect both sides of the body at the same time and may spread to the upper arms, hips and thighs. Patients may have difficulty getting out of chairs or holding an object above their heads. In some cases, muscle weakness can become severe enough that patients struggle to hold their heads up.

In addition, patients typically experience a patchy, dusky, reddish or purple rash that affects the face, and areas around the elbows, knuckles (Gottron’s papules), knees, nails, chest and back. A reddish-purple swelling also may occur around the eyes (heliotrope rash). Areas of skin that are affected tend to be more sensitive to exposure to the sun than other areas of skin. In some cases, this rash may appear a few weeks before muscle weakness is noticed. In other cases patients develop the characteristic rash without ever experiencing muscle weakness. This condition is known as amyopathic dermatomyositis.

Certain symptoms are more likely to affect children than adults. Children with dermatomyositis may have a thickening and hardening of the skin that mimics scleroderma (a progressive disease that leads to hardening and tightening of the skin and connective tissues). This form of dermatomyositis is known as sclerodermatomyositis.

People with dermatomyositis are also at increased risk for infections, particularly infections involving the respiratory system and digestive system.

Children are also more likely than adults to have gastrointestinal ulcers and infections, or to develop hardened deposits of calcium that form under the skin. This latter condition is known as calcinosis, and it appears as hard bumps under the skin. Calcinosis most often appears on the fingers, hands, elbows and knees. Sometimes these lumps break the skin, causing painful sores that may become infected. Calcinosis tends to be diagnosed later in the progression of dermatomyositis.

Some people may experience contractures, which occur when a muscle shortens, forcing the joint to stay bent (e.g., the ankle). Contractures tend to develop later in the chronic stages of dermatomyositis and are more likely in children who do not receive physical therapy.

Other symptoms often associated with dermatomyositis include fatigue, itchiness, fever and weight loss. Some patients may develop an itchy, scaly, burning scalp and experience hair thinning. Hair typically grows back after treatment.

Symptoms may worsen in women during pregnancy. Active dermatomyositis also increases the risk of premature birth and stillbirth. However, these risks are diminished when a women’s dermatomyositis is in remission.

Sudden shortness of breath may indicate that the chest muscles have been damaged, whereas swallowing problems (dysphagia) may indicate that the muscles of the throat or esophagus have been damaged. These symptoms become more severe in patients who have dermatomyositis. Patients who experience these symptoms are encouraged to seek medical care promptly.

In worst-case situations, dermatomyositis can cause a combination of muscle weakness, malnutrition, pneumonia or respiratory failure that can be fatal. Other disorders associated with dermatomyositis include kidney failure, cancer and abdominal disorders.