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|Classification and external resources|
|ICD-10||M33.0-M33.1 (ILDS M33.910)|
|Classification and external resources|
|ICD-10||M33.0-M33.1 (ILDS M33.910)|
Dermatomyositis (DM) is a connective-tissue disease related to polymyositis (PM) that is characterized by inflammation of the muscles and the skin. While DM most frequently affects the skin and muscles, it is a systemic disorder that may also affect the joints, the esophagus, the lungs, and, less commonly, the heart.
The cause is unknown, but it may result from either a viral infection or an autoimmune reaction. In the latter case it is a systemic autoimmune disease. Many people diagnosed with dermatomyositis were previously diagnosed with infectious mononucleosis and Epstein-Barr virus. Some cases of dermatomyositis actually "overlap" (i.e. co-exist with or are part of a spectrum that includes) other autoimmune diseases such as Sjögren's syndrome, lupus, scleroderma, or vasculitis. Because of the link between dermatomyositis and autoimmune disease, doctors and patients suspecting dermatomyositis may find it helpful to run an ANA - antinuclear antibody - test, which in cases of a lupus-like nature may be positive (usually from 1:160 to 1:640, with normal ranges at 1:40 and below).
Several cases of polymyositis and dermatomyositis were reported as being triggered by the use of various statin drugs used to control blood cholesterol. Muscle biopsies of these patients showed rhabdomyolysis, and degeneration and regeneration of muscle tissue.
High blood levels of creatine kinase (CPK) showed greater than 5 times the normal levels also supporting the rhabdomyolysis findings[clarification needed]. CPK is an enzyme found mainly in heart, brain, and skeletal muscle that tends to rise when inflammation occurs during normal exercise. When these levels rise in excess of the normal level (less than 200), and become more than five times higher, severe cell damage to the muscles, brain, and heart ensue[clarification needed]. The higher the CPK, the greater the cellular damage done[clarification needed]. Extremely high levels of CPK cause rhabdomyolysis to these muscles and organs[clarification needed]. Without treatment, kidney damage occurs and death in the more severe cases. Confirmed polymyositis with the skin signs is known as dermatomyositis.
Some cases of dermatomyositis are a paraneoplastic phenomenon, indicating the presence of cancer. In cases involving cancer, the cancer is usually pre-existent, with removal of the cancer resulting in remission of the dermatomyositis. The onset of a rash in patients with pre-existing myositis requires investigation of the neoplastic possibility.
In his 1988 article, Clinical pathologic correlations of Lyme disease by stage, noted Lyme disease researcher Dr. Alan Steere observed, "[...] the perivascular lymphoid infiltrate in clinical myositis does not differ from that seen in polymyositis or dermatomyositis. All of these histologic derangements suggest immunologic damage in response to persistence of the spirochete, however few in number."
Dermatomyositis occurs more commonly in female patients. It presents as a proximal symmetrical muscle weakness with vasculitis affecting the skin, muscles and internal organs. Patients find it hard to raise their arms to comb their hair or walk up the stairs due to the proximal muscle weakness. It can be severe enough to affect the muscles needed for speech and swallowing and is also known to cause respiratory compromise. Calcinosis can occur in the skin, joints and tissues. Upon investigation, characteristically one would find an elevated ESR and CPK along with typical EMG findings of spontaneous muscle fibrillation and short polyphasic muscle potentials.
Gottron's papules, scaly erythematous eruptions or red patches overlying the knuckles, elbows, and knees are a characteristic feature of Dermatomyositis. Other skin manifestations involve periungual telangiectasias and a heliotropic (purple) rash over the upper eyelids.
X-ray findings sometimes include dystrophic calcifications in the muscles, and patients may or may not notice small calcium deposits under the skin. Many do not have any calcium deposits of any kind. The rash also may come and go, and may not be dependent on the severity of the muscle involvement at the time. "Gottron's papules" (pink patches on the knuckles and other extensor surfaces) and priapism are associated with this disorder.
The main symptoms include skin rash and symmetric proximal muscle weakness which may be accompanied by pain. The pain may resemble the type experienced after strenuous exercise. Some dermatomyositis patients have little pain, while in others (esp. in JDM), the pain may be severe. It is important to remember that this condition varies from person to person in many ways. Also in many cases muscle may deteriorate and render the patient temporarily paralyzed unable to walk, run, get out of bed, or even swallow food and liquids.
Skin findings occur in dermatomyositis but not PM and are generally present at diagnosis. Gottron's sign is an erythematous, scaly eruption occurring in symmetric fashion over the MCP and interphalangeal joints (can mimic psoriasis). The heliotrope or "lilac" rash is a violaceous eruption on the upper eyelids and in rare cases on the lower eyelids as well, often with itching and swelling (most specific, though uncommon)[clarification needed]. Shawl (or V-) sign is a diffuse, flat, erythematous lesion over the back and shoulders or in a "V" over the posterior neck and back or neck and upper chest, which worsens with UV light. Erythroderma is not a flat, erythematous lesion similar to the shawl sign but located in other areas, such as the malar region and the forehead. Periungual telangiectasias and erythema occur.
Mechanic's hands (also in PM) refers to rough, cracked skin at the tips and lateral aspects of the fingers forming irregular dirty-appearing lines that resemble those seen in a laborer (this is also associated with the anti-synthetase syndrome). See: sclerodactyly. Psoriaform changes in the scalp can occur. Centripetal flagellate erythema comprises linear, violaceous streaks on the trunk (possibly caused by itching pruritic skin). Calcinosis cutis (deposition of calcium in the skin) is usually seen in juvenile dermatomyositis, not adult dermatomyositis. Dysphagia (difficulty swallowing) is another feature, occurring in as many as 33% of cases.
There is a form of this disorder that strikes children, known as juvenile dermatomyositis (JDM). For the most part juvenile dermatomyositis is the same as the adult form, but the relationship with cancer is far lower, or non-existent.
Cross sections of muscle reveal muscle fascicles with small, shrunken polygonal muscle fibers on the periphery of a fascicle surrounding central muscle fibers of normal, uniform size.
Aggregates of mature lymphocytes with small, dark nuclei and scant cytoplasm are seen surrounding vessels. Other inflammatory cells are distinctly uncommon. Immunohistochemistry can be used to demonstrate that both B- and T-cells are present in approximately equal numbers.
The diagnosis of dermatomyositis can be confirmed by muscle biopsy, EMG,and blood tests. It should be noted, however, that only muscle biopsy is truly diagnostic; liver enzymes and EMG are relatively non-specific. Other enzymes, specifically creatine phosphokinase (CPK), are the major tool in assessing the progress of the disease and/or the efficacy of treatment. On the muscle biopsy, there are two classic microscopic findings of dermatomyositis. They are:
Dermatomyositis must be differentiated from other common, lymphocyte predominant inflammatory myopathies. If present, the characteristic perifascicular atrophy makes this distinction trivial.
There is some overlap in the microscopic appearances of different inflammatory myopathies, but some helpful differences are often present. The rimmed vacuoles of inclusion body myositis (IBM) are absent in dermatomyositis. Polymyositis is characterised by diffuse or patchy inflammation of the muscle fascicles, a random pattern of muscle atrophy, and T-cell predominance with T-cells seen invading otherwise viable appearing muscle fibers. Dermatomyositis has been associated with cases of Lyme Disease.
This disease has no known cure. Specialized exercise therapy may supplement treatment to enhance quality of life.
Medications to help relieve symptoms include:
Before the advent of modern treatments such as prednisone, intravenous immunoglobulin, plasmapheresis, chemotherapies, and other drugs, the prognosis was poor. Now there are numerous treatments and immunomodulatory drugs. Fortunately, more than 90% of patients today will do well for many years, with remission being a possibility. However, it is still important that treatment begin as soon as possible.
Gottron's papules. Erythematous plaques overlying the elbows in a patient with juvenile dermatomyositis. In some patients, small erythematous plaques may overly the extensor aspects of larger joints, such as the elbows, knees, and medial malleoli. This is considered to be an extended part of the spectrum of Gottron's papules.
Gottron's papules. Erythematous plaques overlying the elbows in a patient with juvenile dermatomyositis. In some patients, small erythematous plaques may overly the extensor aspects of larger joints, such as the elbows, knees, and medial malleoli. This is considered to be an extended part of the spectrum of Gottron's papules. Note in Figure, a focal area of dystrophic calcification at the site of Gottron's papules, which is indicative of damage, as discussed below.
Heliotrope is often associated with periorbital edema and telangiectasias of the upper eyelids. In the resolution stage, atrophy or dyspigmentation (hypo- or hyperpigmentation) may be apparent. Heliotrope. Subtle erythema and minimal edema involving both upper eyelids, with extension to the lower eyelids.