Definition of Dermatomyositis – Symptoms, Causes and Diagnosis

What is it? It is a type of inflammatory myopathy characterized by inflammatory and degenerative changes in muscles and skin.

Associated symptoms and physical findings can vary widely from case to case, as patients may present themselves differently.

Muscular abnormalities may begin with pain and weakness of the muscles of the trunk, arms, hips, and thighs (proximal muscles). The muscles may be stiff, sore, tender, and, eventually, show signs of degeneration (atrophy).

Affected individuals may experience difficulties performing certain functions, such as raising their arms and climbing stairs or developing speech and swallowing problems.

Skin abnormalities associated with Dermatomyositis often include a distinctive reddish-purple rash (heliotrope eruption) on the upper eyelid or across the cheeks and bridge of the nose in a “butterfly” pattern and on the forehead and the scalp.

Other characteristic eruptions include scaling and reddening of the knuckles, elbows, knees, and other extensor regions (blemishes and signs of Gottron); An abnormal accumulation of fluid (edema) in the body tissues surrounding the eyes; and other features.

The symptoms of juvenile Dermatomyositis are similar to those associated with the adult form of the disorder. However, the onset is usually more sudden.


In addition, abnormal accumulations of calcium deposits (calcifications) in the muscles and tissues of the skin and the involvement of the digestive tract are more common in the juvenile.

Inflammatory myopathies are a group of diseases that involve inflammation and chronic muscle weakness.

They are thought to be autoimmune diseases. The body’s natural defenses (antibodies, lymphocytes, etc.) against invading organisms suddenly start to attack perfectly healthy tissue for unknown reasons, leading to inflammation or swelling.

Signs and symptoms of Dermatomyositis

In those with Dermatomyositis, the onset of symptoms may be gradual (insidious) or sudden (acute). The symptoms often stop and subside for no apparent reason.

The main symptom of the disorder is muscle weakness, which often affects the trunk and muscles closest to the trunk (i.e., the proximal muscles), such as the hips, thighs, shoulders, arms, and neck.

The affected muscles may be stiff, sore, and sensitive and may show muscle wasting and degeneration (atrophy).

Muscle weakness and the progress of degeneration can lead to an uncomfortable form of walking and a gradual inability to perform specific tasks, such as raising the arms, climbing stairs, or getting dressed.

Characteristic signs may include an inability to lift the head of the pillow when lying down or to get up without help from the ground. In some people with the disorder, the involvement of the muscles of the neck, tongue, and throat can result in difficulty swallowing (dysphagia) and articulate speech (dysphonia).

In exceptional cases, the weakening of the chest wall muscles and the diaphragm can cause breathing difficulties, leading to life-threatening complications without proper and timely treatment.

In addition, in some with long-term chronic disease, certain joints can be fixed in a permanently bent (flexed) position and cause problems in walking.


The specific underlying causes of Dermatomyositis remain unknown. However, the evidence suggests that genetic, immunological, and environmental factors play some role.

The underlying genetic and immune mechanisms may be suggested by several findings, including a higher frequency of certain genetically determined elements or “human leukocyte antigens” in individuals with the disorder.


HLA are proteins that play an essential role in the body’s immune system, influence the outcome of a transplant, and seem to affect an individual’s predisposition to certain diseases.

Evidence suggests that specific HLA has an increasing frequency in children and adults with Dermatomyositis. However, the particular implications of these findings are not fully understood.

It is believed that Dermatomyositis belongs to a group of disorders in which the body’s natural immune defenses misbehave against the body’s tissues (autoimmune diseases).

In Dermatomyositis, an abnormal immune reaction seems to lead to obstructive inflammatory changes of the blood vessels within the muscle, the connective tissues of the skin, and other tissues; Irregular degeneration, wear (atrophy), and regeneration of muscle fibers; Thinning of the outermost superficial layer (epidermis); and other associated findings.

Affected populations

Dermatomyositis can occur at any time from infancy to approximately 80 years, but most commonly occurs between the ages of 40 to 60.

The estimated incidence of Dermatomyositis is 9.63 cases per million inhabitants. In children, symptoms usually appear between the ages of five to 15 years.

Approximately three out of every 1,000,000 children are affected by juvenile Dermatomyositis. Females are affected by Dermatomyositis twice as often as males.


Dermatomyositis can be diagnosed based on a detailed history of the patient, a thorough clinical examination, the detection of characteristic physical findings, and specific specialized tests.

The diagnostic findings include:

  • The presence of the characteristic skin rash.
  • Progressive weakness of the proximal muscles.
  • Elevated levels of certain muscle enzymes (i.e., creatine kinase [CQ], aldolase, aspartate aminotransferase, lactic dehydrogenase) in the liquid portion of the blood (serum) may be suggestive of muscle inflammation.

Abnormal findings in electromyography (EMG).

The EMG is a test that records the electrical activity in skeletal (voluntary) muscles at rest and during muscle contraction. In some cases, doctors may also recommend MRI, during which a magnetic field and radio waves create detailed cross-sectional images of specific tissues.

Muscle biopsies can sometimes be recommended to help detect specific changes that can help confirm the diagnosis. Muscle biopsy involves the removal and microscopic examination of small muscle tissue samples.

Experts indicate that muscles recently tested with EMG should be avoided since the procedures can cause inflammatory changes that lead to false-positive results after biopsy.

Additional imaging studies may aid in diagnosing Dermatomyositis and may include: computed tomography, chest x-ray, barium swallow, and ultrasound of affected muscles.