Polymyositis and dermatomyositis are inflammatory myopathies, usually idiopathic, characterized by diffuse inflammation of striated muscle, expressed clinically by muscle fatigue which has proximal location (in polymyositis) associated with skin rash (in dermatomyositis). Polymyositis and dermatomyositis are rare diseases that can occur at any age, usually between 5 and 15 years in children and among adults between 40 to 60 years. This disease is twice as common in women than in men.
Bohan and Peter proposed the following classification of inflammatory myopathies:
- Type I: Adult idiopathic polymyositis;
- Type II: Adult idiopathic dermatomyositis;
- Type III: dermatomyositis or polymyositis associated with neoplasia;
- Type IV: dermatomyositis or polymyositis of the children associated with vasculitis;
- Type V: polymyositis and dermatomyositis associated with other connective tissue diseases (overlap syndromes);
- Type VI: inclusion-bodies myositis;
- Type VII: eosinophilic myositis, giant cell myositis and ossificant myositis.
The pathogenesis is incompletely known, but assume that different causal factors are involved, acting through autoimmune mechanism.
Genetic susceptibility by implication of genes like HLA DR3 and HLA DRW52;
Retrovirus infections, especially Epstein-Barr and Coxsackie. These viruses appear to initiate an autoimmune myositis by molecular mimetism with some muscle antigens.
Pathogenic mechanism is immunological. Antigens against which triggers the autoimmune response are unknown, probably of muscular and microvascular nature.
Antibodies have uncertain role and are represented by:
- cytoplasmic antibodies: anti-RNA t synthetase, anti-SRP;
- nuclear antibodies: Anti I-2.
Muscular manifestations: muscle fatigue accompanied by muscle weakness, usually painless, is the main symptom. It occurs slowly, is symmetrical and can affect any muscle. Appears initially at the proximal segment:
- pelvic belt: is interested in more than 90% of cases and lead to failure in flexion of the copse on the abdomen and difficulties in climbing stairs;
- scapular belt: is affected in more than 85% of cases and makes it difficult to raise arms and combing;
- flexors muscles of the neck: raising the head with difficulty from the pillow and difficulty in maintaining orthostatic position.
Skin Manifestations are present in dermatomyositis and are expressed by:
- heliotrope rash (occurs after exposure to the sun) is located on the face (periorbital red rash with swelling of the eyelids), neck (shaped “V” erythema) and shoulders ( erythema in the form of a scarf);
- Gottron sign: maculopapular lesions, consisting of prominent red, scaly spots, which are localized on the dorsal part of the proximal interphalangeal and metacarpophalangeal joints, elbows, knees and external malleolus;
- nail telangiectasia;
- calcifications of soft tissues (skin, subcutaneous tissue and fascia);
- hands with irregular, thickened and cracked skin.
Articular Manifestations: arthralgia, arthritis which is not erosive and deforming.
Gastrointestinal disorders: dysphagia by involving striated musculature of the oropharynx and upper esophagus (this is a sign of poor prognosis) and gastro-intestinal ulcers.
Cardiac and pulmonary manifestations are less common than in other connective tissue diseases and occur in severe forms of disease. May occur arrhythmias, myocarditis, heart failure, pneumonia and respiratory muscle damage.
Cancers are more common in patients with dermatomyositis: ovarian cancer, breast cancer, colon cancer, lung cancer and melanoma.
- Increased muscle enzymes: CPK, CPK-MM, ALT, AST, LDH. CPK is the most sensitive, it can increase in the active form of the disease up to 10-50 times and evolve parallel with disease activity;
- Electromyography shows suggestive changes of inflammatory myopathy: spontaneous fibrillation at rest, action potential of short duration and small amplitude produced by muscle contraction;
- Muscle and skin biopsy allow the histopathologic diagnosis.
The diagnosis of polymyositis and dermatomyositis is based on laboratory explorations and on Bohan and Peter criteria for inflammatory myopathies. The criteria are:
- Symmetric weakness in the belts, neck and extremities with progressive decline within a few weeks or months, which may be associated with dysphagia or respiratory muscle involvement;
- Increased muscle enzymes: CPK, CPK-MM, ALT, AST, LDH;
- Electromyographic abnormalities;
- Muscle biopsy: inflammation, necrosis, regeneration, atrophy.
If there are four criteria the diagnosis is certain, if three criteria are present then the diagnosis is probable and if two criteria are present then the diagnosis is possible.
Therapy aims to suppress the inflammatory process in order to reduce destructive extensive muscle. The treatment depends on the clinical presentation and is done in steps:
- Step I: high-dose of prednisone;
- Stage II: azathioprine or methotrexate;
- Stage III: intravenous immunoglobulin;
- Stage IV: cyclosporine, chlorambucil, cyclophosphamide and mycophenolate.
In exacerbations of disease is recommended bed rest. The surgical treatment is offered only if the cancer is associated and consists of removing the tumor, thereby improving symptoms or even cure the disease.