Diagnosis
The diagnosis of dermatomyositis is based on five criteria, which are also used to differentially diagnose with respect to polymyositis:
Muscle weakness in both thighs or both upper arms
Using a blood test, finding higher levels of enzymes found in skeletal muscle, including creatinine kinase, aldolase, and glutamate oxaloacetate, pyruvate transaminases and lactate dehydrogenase
Using testing of electric signalling in muscles, finding all three of: erratic, repetitive, high-frequency signals; short, low-energy signals between skeletal muscles and motor neurons that have multiple phases; and sharp activity when a needle is inserted into the muscle
Examining a muscle biopsy under a microscope and finding mononuclear white blood cells between the muscle cells, and finding abnormal muscle cell degeneration and regeneration, dying muscle cells, and muscle cells being consumed by other cells (phagocytosis)
Rashes typical of dermatomyositis, which include heliotrope rash, Gottron sign, and Gottron papulesThe fifth criterion is what differentiates dermatomyositis from polymyositis; the diagnosis is considered definite for dermatomyositis if three of items 1 through 4 are present in addition to 5, probable with any two in addition to 5, and possible if just one is present in addition to 5.Dermatomyositis is associated with autoantibodies, especially antinuclear antibodies (ANA).
Dermatomyositis (DM) is a long-term inflammatory disorder which affects skin and the muscles. Its symptoms are generally a skin rash and worsening muscle weakness over time. These may occur suddenly or develop over months. Other symptoms may include weight loss, fever, lung inflammation, or light sensitivity. Complications may include calcium deposits in muscles or skin.The cause is unknown. Theories include that it is an autoimmune disease or a result of a viral infection. Dermatomyositis may develop as a paraneoplastic syndrome associated with several forms of malignancy. It is a type of inflammatory myopathy. Diagnosis is typically based on some combination of symptoms, blood tests, electromyography, and muscle biopsies.While no cure for the condition is known, treatments generally improve symptoms. Treatments may include medication, physical therapy, exercise, heat therapy, orthotics and assistive devices, and rest. Medications in the corticosteroids family are typically used with other agents such as methotrexate or azathioprine recommended if steroids are not working well. Intravenous immunoglobulin may also improve outcomes. Most people improve with treatment and in some, the condition resolves completely.About one per 100,000 people per year are newly affected. The condition usually occurs in those in their 40s and 50s with women being affected more often than men. People of any age, however, may be affected. The condition was first described in the 1800s. Signs and symptoms
The main symptoms include several kinds of skin rash along with muscle weakness in both upper arms or thighs.