Diagnosis of juvenile dermatomyositis

Non-invasive research methods

Electrocardiography

The ECG reveals signs of metabolic disturbances in the myocardium, tachycardia. In myocarditis, conduction slowdown, extrasystoles, and decreased electrical activity of the myocardium are recorded. Occasionally, ischemic changes in the heart muscle are observed - a reflection of generalized vasculopathy affecting the coronary vessels.

Echocardiographic examination

EchoCG in myocarditis shows dilation of the heart cavities, thickening and/or hyperechogenicity of the walls and/or papillary muscles, decreased contractile and pumping function of the myocardium, and in pericarditis - dissection or thickening of the pericardial layers.

Ultrasound examination of abdominal organs

Ultrasound data reveals non-specific changes in the liver and spleen: increased vascular pattern and/or echogenicity of the parenchyma.

Spirography

The spirogram (conducted after 5 years) shows restrictive changes as a result of a decrease in the strength of respiratory movements.

Chest X-ray

In most patients, the radiograph shows an increase in the vascular pattern, sometimes local, and in rare cases, changes in the pulmonary interstitium, and a high position of the diaphragm as a result of its paresis. In patients who have not received treatment for a long time, deformation of the pulmonary pattern is formed.

Electromyography

On the electromyogram (EMG), with a normal speed of nerve impulse conduction, the myogenic nature of changes is determined in the form of a decrease in the amplitude and shortening of the duration of the action potentials of muscle fibers, spontaneous activity in the form of fibrillations.

Laboratory research

Complete blood count

A general blood test in the acute period of juvenile dermatomyositis is usually unchanged or there is a moderate increase in ESR (20-30 mm/h), slight leukocytosis (10-12x10 ⁹ /l), normochromic anemia, however, often these changes are due to an association with infection.

Biochemical blood test

Increased levels of "muscle breakdown enzymes" (CPK, LDH, AST, ALT, aldolase) that have diagnostic value. In acute processes, progressive skeletal muscle damage, the levels of CPK and LDH exceed the norm by 10 times or more. The level of CPK at the time of the initial examination is elevated in 2/3 of patients with juvenile dermatomyositis. The level of LDH, being a less specific but more sensitive test, is elevated in 4/5 patients, but to a lesser extent; during treatment, it remains elevated longer. The level of AST exceeds the norm more often and to a greater extent than ALT. It is advisable to examine the level of all 5 enzymes in the blood serum in juvenile dermatomyositis due to the fact that in one patient, at certain intervals, the level of only one of them may be elevated.

Immunological examination

During the active period of the disease, some immunological changes are detected. Determination of myositis-specific antibodies is not used in practice due to the low frequency of their detection in the juvenile form of the disease. Only in interstitial pulmonary syndrome does determination of anti-jo-1 antibodies have practical value.

Currently, positive ANF in the active phase of the disease is detected in 50-86% depending on the sensitivity of the technique (as a rule, not in such a high titer as in systemic lupus erythematosus), usually reaching 1:40-1:80. Approximately 1/4 of patients in the active period can be found to have an increased IgG level, every tenth patient has a positive rheumatoid factor. In severe vasculitis syndrome, reactions to antibodies to cardiolipins (ACL) are positive.

Invasive research methods

Muscle biopsies reveal changes of an inflammatory and degenerative nature: cellular infiltration between muscle fibers and around small vessels with a predominance of lymphocytes, with the participation of histiocytes and plasma cells; necrosis of muscle fibers with loss of transverse striation, elements of regeneration. In the chronic process, atrophy of muscle fibers and signs of interstitial fibrosis predominate.

In our opinion, in typical cases the diagnosis is established based on the clinical picture and laboratory data. EMG and muscle biopsy data do not always correspond to the established criteria due to artifacts and sclerotic changes that distort the results, therefore these diagnostic methods should be used in controversial, unclear cases.

Differential diagnostics

Differential diagnosis of juvenile dermatomyositis is carried out with a large number of diseases.

Juvenile polymyositis very rarely develops in childhood. It is characterized by weakness of the proximal and distal parts of the limbs, hypotension, dysphagia. The disease is often chronic and poorly treatable with glucocorticosteroids. A muscle biopsy is necessary to confirm the diagnosis. Polymyositis in the first year of life may be a manifestation of intrauterine infection.

Infectious myositis is caused by viruses, protozoa and bacteria. Viral myositis is caused by influenza viruses A and B, coxsackie B, the disease lasts 3-5 days, accompanied by severe myalgia, fever, catarrhal and general symptoms.

The clinical picture of toxoplasmosis resembles dermatomyositis.

Trichinellosis is accompanied by fever, diarrhea, abdominal pain, eosinophilia, swelling of the periorbital space and muscles, most often the face, neck and chest.

Neuromuscular diseases and myopathies (Duchenne muscular dystrophy, Myasthenia gravis, myotonia, etc.) are characterized by the absence of typical skin manifestations.

Duchenne muscular dystrophy is characterized by slowly progressive muscle weakness (mainly proximal) in the absence of muscle hardening, and is hereditary in nature.

Myasthenia gravis is characterized by involvement of the ocular and distal muscles of the extremities, and a decrease in the feeling of weakness after the administration of cholinergic drugs.

Myositis in other systemic connective tissue diseases, in particular in systemic lupus erythematosus, overlap syndromes, systemic scleroderma, is quite pronounced, accompanied by myalgia, distinct muscle weakness and increased levels of "muscle breakdown enzymes". In such cases, the severity of other clinical symptoms and the presence of immunological markers of other systemic connective tissue diseases are important in diagnostics.

Ossifying myositis progressiva (Munchmeyer disease) is a rare, inherited, autosomal dominant disorder characterized by fibrosis and calcification of large axial muscles, leading to stiffness and severe disability. The process begins in the muscles of the neck and back, spreading to the extremities.

It is important to remember that muscle weakness can be a manifestation of some endocrinopathies (hypo- and hyperthyroidism, hypo- and hyperparathyroidism, diabetes mellitus, steroid myopathy, Addison's disease, acromegaly), metabolic disorders (glycogen storage diseases, mitochondrial myopathy), toxic and drug-induced myopathy (D-penicillamine, colchicine, etc.)

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