Dermatomyositis is an acquired idiopathic inflammatory myopathy with characteristic skin manifestations and symmetrical proximal muscle weakness. Dermatomyositis’ cardinal symptom is a skin rash that precedes, accompanies, or follows progressive muscle weakness.
Dermatomyositis may occur at any time from infancy through approximately age 80, but most commonly it occurs between ages 40 to 60. The estimated incidence of dermatomyositis is 9.63 cases per million population. In children, the symptoms usually appear between the ages of five to 15 years. Approximately three in 1,000,000 children are affected by juvenile dermatomyositis. This subgroup of patients has a better prognosis than adult patients. Females are affected by dermatomyositis twice as often as males.
In many patients, the first sign of dermatomyositis is the presence of a symptomless, itchy or burning rash. Cutaneous involvement may manifest as follows:
- Reddish or bluish-purple patches, on photo-exposed surfaces
- Purple eyelids, which are described as heliotrope, as they resemble the heliotrope flower.
- Eruption on the dorsal hands, particularly over the knuckles, which are known as Gottron papules
- Ragged cuticles and prominent blood vessels on nail folds
- The rash may also affect cheeks, nose, shoulders, upper chest and elbows
- Scaly scalp or diffuse hair loss
Less commonly there is poikiloderma i.e. the skin is atrophic (pale, thin skin), red (dilated blood vessels) and brown (post-inflammatory pigmentation)
Muscle involvement manifests as the following:
- Proximal muscle weakness
- Muscle fatigue/weakness when climbing stairs, walking, rising from a seated position, combing hair, or reaching for items above shoulders
- Difficulty swallowing (dysphagia)
- Muscle tenderness: May occur, but not a typical feature of dermatomyositis
Adults with dermatomyositis may experience weight loss, a low-grade fever, inflamed lungs, and be sensitive to light such that the rash or muscle disease gets worse. Children and adults with dermatomyositis may develop calcium deposits, which appear as hard bumps under the skin or in the muscle (called calcinosis). Calcinosis most often occurs 1-3 years after the disease begins. These deposits are seen more often in children with dermatomyositis than in adults.
The specific underlying cause(s) of dermatomyositis remain unknown. Some studies have reported an association with histocompatibility antigens, environmental agents (e.g., virus, drugs) and autoimmunity. Dermatomyositis is thought to belong to a group of disorders in which the body’s natural immune defenses inappropriately act against the body’s own tissues (autoimmune disorders). In dermatomyositis, an abnormal immune reaction appears to lead to obstructive inflammatory changes of blood vessels within muscle, connective tissues of the skin, and other tissues; patchy degeneration, wasting (atrophy), and regeneration of muscle fibers; thinning of the outermost skin layer (epidermis); and/or other associated findings.
The diagnosis of dermatomyositis is usually recognized by the typical heliotrope rash. Patients with a characteristic skin eruption should have a skin biopsy performed to confirm the diagnosis. Additional tests can be ordered to help confirm the diagnosis or to determine the extent of the disease. Blood work measuring creatine kinase and aldolase can help measure the extent of muscle damage. The presence of circulating autoantibodies in the blood may indicate the autoimmune disease. MRI may detect inflammation in the muscles. Electromyography (EMG) testing done by a small electrode inserted into the muscle can measure the electrical activity of the muscle. The muscle biopsy is a very important test for confirming the diagnosis and excluding other inflammatory muscular diseases.
There is no cure for dermatomyositis, but the symptoms can be treated. Options include medication, physical therapy, exercise, heat therapy (including microwave and ultrasound), orthotics and assistive devices, and rest. The aim of treatment is to eliminate inflammation and restore muscle performance. Initial treatment includes high-dose corticosteroids. Dosage is then tapered to reach an appropriate maintenance dose. Immunosuppressive agents are also frequently used in combination, typically methotrexate, azathioprine, and mycophenolatemofetil. Intravenous immunoglobulin (IVIg) or intravenous methylprednisolone (IVMP) may be used in severe cases. Physical therapy is also recommended. Topical corticosteroid and tacrolimus have been used to treat skin manifestations. Patients should avoid direct UV light and use high-factor sunscreen. Monitoring for extra muscular involvement should include chest X-ray and pulmonary function testing. If cardiac involvement is suspected, echocardiography is recommended. Age-appropriate cancer screening is also recommended.
Regular follow-up and screening, especially in the first three years after diagnosis, is required because of the association with underlying cancer that may not be present at the time of diagnosis. Symptoms may go away completely in some people, such as children. The condition may be fatal in adults due to severe muscle weakness, malnutrition, pneumonia, or lung failure. The major causes of death with this condition are cancer and lung disease.
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