Polymyositis and dermatomyositis: causes, symptoms, diagnosis, treatment

Polymyositis and dermatomyositis are rare systemic rheumatic diseases characterized by inflammatory and degenerative muscle changes (polymyositis) or muscles and skin (dermatomyositis). The most specific skin manifestation is a heliotrope rash.

The muscle lesions are symmetrical and include weakness, some soreness and subsequent atrophy of the proximal muscles of the upper extremity belt. Complications can include internal organ damage and malignancy. Diagnosis is based on the analysis of the clinical picture and evaluation of muscle disorders by determining the concentrations of the relevant enzymes, performing MRI, electromyography and biopsy of muscle tissue. The treatment uses glucocorticoids, sometimes in combination with immunosuppressants or immunoglobulins administered intravenously.

Women are sick twice as often as men. The disease can occur at any age, but is more often detected in the interval from 40 to 60 years; in children from 5 to 15 years.

[1], [2], [3]

What causes dermatomyositis and polymyositis?

The cause of the disease is supposed to be an autoimmune reaction to muscle tissue in genetically predisposed individuals. The disease is more common in the presence of a burdened family history and carriers of some HLA antigens (DR3, DR52, DR56). Possible start-up factors are viral myositis and malignant neoplasms. There are reports of the detection in muscle cells of structures similar to picornaviruses; In addition, viruses can induce similar diseases in animals. The association of malignant tumors with dermatomyositis (much less often than with polymyositis) suggests that tumor growth can also be a trigger mechanism for the development of the disease as a result of triggering autoimmune reactions to common tumor and muscle antigens.

In the walls of the blood vessels of skeletal muscles, deposits of IgM, IgG and the third complement component are detected; this is especially true in children with dermatomyositis. Patients with polymyositis may also develop other autoimmune processes.

Pathophysiology of dermatomyositis and polymyositis

Pathological changes include cell damage and their atrophy against a background of inflammation of varying severity. The muscles of the upper and lower extremities, as well as the face, are less affected than other skeletal muscles. The defeat of the visceral musculature of the pharynx and the upper parts of the esophagus, less often of the heart, stomach or intestine, can lead to a disruption in the functions of these organs. High concentrations of myoglobin, caused by rhabdomyolysis, can cause kidney damage. There may also be inflammatory changes in the joints and lungs, especially in patients who have antisynthetic antibodies.

Symptoms of dermatomyositis and polymyositis

The onset of polymyositis can be acute (especially in children) or subacute (usually in adults). Acute viral infection sometimes precedes or is the starting factor of the manifestation of the disease, the most frequent manifestations of which are weakness of proximal muscles or skin rashes. Pain sensations are less expressed than weakness. Perhaps the development of polyarthralgia, the phenomenon of Raynaud, dysphagia, violations of the lungs, common symptoms (fever, lowering its mass, weakness). The phenomenon of Reynaud is often found in patients who have concomitant connective tissue diseases.

Muscle weakness may progress for several weeks or months. However, for the clinical manifestation of muscle weakness, a minimum of 50% of the muscle fibers must be affected (thus, the presence of muscle weakness indicates progression of the myositis). Patients may experience difficulty lifting their arms above shoulder level, walking up the stairs, rising from sitting. Due to the pronounced weakness of the pelvic muscles and the shoulder girdle, patients can be riveted to a wheelchair or bed. With defeat of the flexor of the neck, it becomes impossible to tear off the head from the pillow. The defeat of the muscles of the pharynx and the upper parts of the esophagus leads to a violation of swallowing and regurgitation. The muscles of the lower, upper limbs and face are usually not affected. However, the development of limb contractures is possible.

Skin eruptions, noted with dermatomyositis, usually have a dark color and erythematous character. Periorbital swelling of purple color (heliotrope rash) is also characteristic. Skin eruptions may slightly rise above the skin level and be smooth or covered with scales; localization of rashes - forehead, neck, shoulders, chest, back, forearms, lower legs, eyebrows, knee areas, medial malleoluses, back surfaces of interphalangeal and metacarpophalangeal joints, lateral side (Gottron's symptom). Possible hyperemia of the base or periphery of the nails. On the skin of the lateral surface of the fingers, it is possible to develop desquamative dermatitis, accompanied by the appearance of cracks. Primary skin lesions are more often resolved without consequences, but can lead to the development of secondary changes in the form of dark pigmentation, atrophy, scars or vitiligo. Possible the formation of subcutaneous calcifications, especially in children.

Approximately 30% of patients develop polyarthralgia or polyarthritis, often accompanied by swelling and joint effusion. Nevertheless, the severity of articular manifestations is low. More often, they occur when patients have antibodies to Jo-1 or other synthetases.

The defeat of the internal organs (with the exception of the pharynx and upper esophagus) in polymyositis is less common than in other rheumatic diseases (in particular, SLE and systemic scleroderma). Rarely, especially with an antisynthetic syndrome, the disease manifests as an interstitial pneumonitis (in the form of dyspnea and cough). Heart arrhythmias and conduction disorders may develop, but they are usually asymptomatic. Manifestations from the gastrointestinal tract are more common in children who also suffer from vasculitis, and may include vomiting with an admixture of blood, melena and perforation of the intestine.

Classification of polymyositis

There are 5 variants of polymyositis.

1. Primary idiopathic polymyositis, which can occur at any age. With it, there is no skin lesion.
2. Primary idiopathic dermatomyositis is similar to the primary idiopathic polymyositis, but with it there is a lesion of the skin.
3. Polymyositis and dermatomyositis associated with malignant neoplasms can occur in patients of any age; most often observed in elderly patients, as well as in patients with other connective tissue diseases. The development of malignant neoplasms can be observed both within 2 years before and within 2 years after the debut of myositis.
4. Children's polymyositis or dermatomyositis is associated with systemic vasculitis.
5. Polymyositis and dermatomyositis can also occur in patients suffering from other connective tissue diseases, most often with progressive systemic sclerosis, mixed connective tissue disease and SLE.

Inclusion of the muscle of the trunk into the group of polymyositis of myositis is incorrect, since the latter is a separate disease characterized by clinical manifestations similar to those of a chronic idiopathic polymyositis. However, it develops in old age, often affects the muscles of the distal parts of the body (for example, the upper and lower extremities), has a longer duration, responds poorly to treatment and is characterized by a typical histological picture.

[4], [5], [6], [7], [8]

Diagnosis of dermatomyositis and polymyositis

Poliomyositis should be suspected in patients with complaints of weakness of proximal muscles, accompanied by their painfulness or without it. Examination for dermatomyositis is necessary for patients complaining of rashes resembling heliotrope or Gotthron symptom, as well as in patients with manifestations of polymyositis, combined with any skin lesions that correspond to dermatomyositis. The clinical manifestations of polymyositis and dermatomyositis may resemble those of systemic sclerosis or, less often, SLE or vasculitis. The reliability of the diagnosis is increased by matching the largest possible number of these five criteria:

1. weakness of proximal muscles;
2. characteristic skin rashes;
3. increased activity of muscle tissue enzymes (creatine kinase or, in the absence of an increase in its activity, aminotransferases or aldolase);
4. characteristic changes in myography or MRI;
5. characteristic histological changes in the biopsy of muscle tissue (absolute criterion).

A muscle biopsy can exclude some clinically similar conditions, such as muscle torso muscle and rhabdomyolysis caused by a viral infection. The changes revealed by histological examination may be different, but typical are chronic inflammation, foci of degeneration and regeneration of muscles. Before the onset of potentially toxic treatment, an accurate diagnosis should be made (usually by histological verification). With MRI, it is possible to identify foci of edema and inflammation in the muscles followed by a targeted biopsy.

Laboratory tests allow reinforcing or, on the contrary, eliminating the suspicion of the presence of the disease, as well as useful in assessing its severity, the possibility of combining with another similar pathology and diagnosing complications. Despite the fact that antinuclear antibodies are detected in some patients, this phenomenon is more typical for other connective tissue diseases. About 60% of patients have antibodies to the nuclear antigen (PM-1) or whole cells of the thymus and Jo-1. The role of autoantibodies in the pathogenesis of the disease remains unclear, although it is known that antibodies to Jo-1 are a specific marker of an antisynthetic syndrome, including fibrosing alveolitis, pulmonary fibrosis, arthritis and the Reino phenomenon.

Periodic assessment of creatine kinase activity is useful for monitoring treatment. Nevertheless, with severe muscle atrophy, the activity of the enzyme may be normal, despite the presence of chronic active myositis. MRI data, muscle biopsies or high values of creatine kinase activity often help differentiate the recurrence of polymyositis and myopathy induced by glucocorticoids.

Since many patients have undiagnosed malignant neoplasms, some authors recommend screening of all adults with dermatomyositis and those suffering from polymyositis over the age of 60 according to the following scheme: physical examination, including breast examination, gynecological examination and examination of the rectum ( including the study of feces for latent blood); clinical blood test; biochemical blood tests; mammography; determination of the cancer embryonic antigen; general urine analysis; chest X-ray. The need for such screening for younger patients who do not have clinical signs of malignant tumors has been questioned by some authors.

[9], [10], [11], [12]

Treatment of dermatomyositis and polymyositis

Before stopping inflammation, it is necessary to limit physical activity. Glucocorticoids are first-line drugs. In the acute stage of the disease, adult patients need prednisolone (inside) at a dose of 40 to 60 mg per day. Regular detection of creatine kinase activity is an early indicator of efficacy: in most patients, its decrease or normalization occurs within 6 to 12 weeks following the increase in muscle strength. After the normalization of the enzyme activity, the dose of prednisolone decreases: first approximately 2.5 mg per day during the week, then more quickly; when the activity of the muscle enzymes increases, the dose of the hormone is increased again. Recovered patients can do without glucocorticoids, but more often adult patients require long-term glucocorticoid therapy (10-15 mg of prednisolone per day). The initial dose of prednisolone for children is 30-60 mg / m ² once a day. If there is a remission> 1 year, children may have a cessation of glucocorticoid therapy.

In some cases, in patients receiving high doses of glucocorticoids, sudden increase in muscle weakness occurs, which may be due to the development of glucocorticoid myopathy.

If an inadequate response to treatment with glucocorticoids, as well as with the development of glucocorticoid myopathy or other complications requiring a dose reduction or withdrawal of prednisolone, immunosuppressants (methotrexate, cyclophosphamide, azathioprine, cyclosporine) should be used. Some patients can receive only methotrexate (usually at doses exceeding those in the treatment of RA) for more than 5 years. Intravenous immunoglobulins can be effective in patients refractory to drug therapy, but their use increases the cost of treatment.

Myositis associated with primary and metastatic tumors, as well as myositis of the trunk muscles, are usually more refractory to glucocorticoid therapy. The development of remission associated with malignant tumors of myositis is possible after removal of the tumor.

What prognosis does dermatomyositis and polymyositis have?

Long-term remission (and even clinical recovery) for 5 years are noted in more than half of treated patients; in children this indicator is higher. Relapse, however, can develop at any time. The overall five-year survival rate is 75%, higher in children. The causes of death in adults are severe and progressive muscle weakness, dysphagia, decreased nutrition, aspiration pneumonia or respiratory failure due to lung infections. Poliomyositis is more severe and resistant to treatment in the presence of damage to the heart and lungs. Death in children can occur due to intestinal vasculitis. The overall prognosis of the disease is also determined by the presence of malignant neoplasms.