Dermatomyositis is a non-purulent inflammatory lesion involving mainly the transverse muscles with a lymphocytic infiltrate and may or may not be associated with a variety of skin lesions. It is characterized clinically by symmetrical weakness of the limb girdle, cervical and pharyngeal muscles, often involving multiple organs, and may be associated with tumors and other connective tissue diseases.
Skin damage in polymyositis and dermatomyositis
The skin lesions of dermatomyositis do not coincide with or parallel the onset of muscle symptoms or the degree of muscle involvement.
Etiology
The exact etiology of the disease is unknown, but it is generally thought to be related to genetics and viral infections. There are significant racial differences in the onset of polymyositis and dermatomyositis. The incidence of polymyositis is highest in African Americans, with a black to white incidence ratio of 3 to 4:1. The incidence of childhood dermatomyositis is higher in Asia and Africa than in Europe and the United States. The presence of the disease in identical twins and first-degree relatives also suggests that it has a genetic predisposition.
Clinical presentation
The disease usually starts insidiously and progresses slowly over weeks, months, or years. Very few patients have an acute onset, with severe muscle weakness, or even rhabdomyolysis, myoglobulinuria and renal failure within days. Patients may have morning stiffness, weakness, loss of appetite, weight loss, fever (low to moderate fever, or even high fever), joint pain, and a few patients have Raynaud’s phenomenon.
1.Muscle manifestations
Muscle involvement is usually bilateral and symmetrical, with scapular and pelvic girdle muscles most commonly involved, followed by cervical and pharyngeal muscles, respiratory muscles are rarely involved, and orbicularis oculi and facial muscles are rarely involved. About half of the patients have myalgia and/or muscle pressure. Myasthenia initially affects the scapular girdle and pelvic girdle muscles, while distal muscle weakness is rare. About half of the patients have cervical muscle involvement, especially cervical flexor muscle involvement, which manifests as difficulty in raising the head when lying down and inability to tilt the head when sitting; pharyngeal or upper transverse esophageal muscle involvement may present with dysphagia, hoarseness and dysphonia, and choking and coughing when ingesting liquid food through the nostrils. Involvement of the smooth muscle of the digestive tract is rare. Weakness of the lower esophageal sphincter can lead to acid reflux and esophagitis, and chronic cases can cause esophageal stricture. When the scapular girdle is involved, there may be difficulty in raising the arm and inability to comb the hair and dress; respiratory muscle weakness may cause chest tightness and difficulty in breathing, and in serious cases, a ventilator is needed to assist breathing; when the patient has pelvic
When patients have pelvic girdle muscle weakness, they may show difficulty in getting up and down steps, inability to stand on their own after squatting or difficulty in standing up from the seat, gait staggering and difficulty in walking.
2. Pulmonary manifestations
Dyspnea during activity is a non-specific but more serious symptom. Polymyositis and dermatomyositis involving respiratory muscles can lead to respiratory muscle weakness. Such patients have difficulty in expelling sputum and are prone to lung infections. The most serious complication is acute progressive alveolitis, which presents with fever, shortness of breath, severe cough, and rapidly progressive dyspnea, which can lead to adult respiratory distress syndrome in severe cases. More common is chronic progressive interstitial pulmonary fibrosis, which presents with progressive dyspnea and whose symptoms are easily masked by symptoms of muscle involvement because of its insidious onset; many other patients have no symptoms of pulmonary involvement and have interstitial fibrosis detected only on radiography and/or pulmonary function tests. On auscultation, a twisting sound at the base of both lungs may be heard.
On X-ray, there is a hairy glassy appearance in the early stage and a reticular or honeycomb shadow in the late stage. Pulmonary function tests show restrictive ventilation impairment and reduced diffusion function. Pulmonary hypertension may develop in advanced stages of the disease, leading to right heart hypertrophy and right heart failure in severe cases. A few patients may have pleuritis and pleural effusion.
3.Heart performance
Cardiac involvement is common, usually mild, and rarely has clinical symptoms. The most common are heart rhythm disturbances, such as palpitations and arrhythmias. Congestive heart failure, which can occur in late stages, is caused by myocarditis or myocardial fibrosis. Occasionally, myocarditis is seen. Myocardial isoenzymes (MB) of creatine kinase (CK) may be elevated, but are not necessarily associated with myocardial involvement and are mostly produced by regenerating myogenic fibers from damaged muscle.
4. Renal lesions
Renal lesions are rare, proteinuria and nephrotic syndrome have been reported occasionally.
5. Skin manifestations
The rash appears before myositis in 55% of patients, simultaneously with myositis in 25%, and after myositis in 15%. The type and extent of the rash varies from person to person, and the rash may be different in the same patient at different stages of the disease. In some patients, the rash and myasthenia gravis may parallel each other, while in others the rash and myasthenia gravis may not be related.
Dermatomyositis has a variety of cutaneous manifestations. One that is diagnostically specific is Gottron’s maculopapular rash or Gottron’s sign. It is commonly seen on the extensor surfaces of the metacarpophalangeal and interphalangeal joints, elbows and knees, and friction-prone areas such as the shoulders and hips. Characteristic rashes include.
① A dark purplish-red rash on the eyelids, especially the upper lid, either on one or both sides, often with periorbital edema and dilated capillaries near the lid margin. In severe cases of edema, both lids obscure the eyes and prevent vision. This purplish
The red rash may also appear on the forehead, cheekbones, bridge of the nose, nasolabial folds, anterior neck, upper chest (V-shaped distribution) and posterior neck, upper back, shoulders and lateral upper arms (shawl-like distribution).
②”Mechanic’s hand”-like changes: skin keratinization, thickening and cracking of finger pads. Hyperkeratosis with follicular keratosis may also be present on the palms, soles, trunk and extremities; smudgy, dark black horizontal stripes appear on the palms and sides of the fingers. It is called “mechanic’s hand” because it is similar to the hand changes of manual laborers. Other skin and mucous membrane changes: red atrophic plaques may appear on the scalp, which are often misdiagnosed as psoriasis or seborrheic dermatitis; dilated capillaries around the nail, or fetish spots. Photosensitivity, phlegmon itch, lipofuscinosis, skin mucin deposition, leukoplakia, multifocal fatty atrophy and Raynaud’s phenomenon have also been reported. Some patients have typical dermatomyositis changes on skin biopsy, with Gottron’s sign and cutaneous manifestations of another type of dermatomyositis, but without the enzymatic changes and clinical signs of dermatomyositis, a condition known as dermatomyositis without myositis. It has been estimated to account for 10% of all dermatomyositis, with some of these patients achieving partial or complete remission over time, some presenting with muscle involvement and signs of muscle weakness, and some presenting with tumors.
Examination
1. Routine laboratory tests
The white blood cell count may be normal or decreased, and 2/3 of the patients may have increased sedimentation. Blood IgG, IgA, IgM, immune complexes and a2 and Y globulin may be increased. Complement C3 and C4 may be reduced.
2.Urinary creatine measurement
The urinary creatine excretion can be increased before the muscle enzyme profile is increased, but this change can occur in various muscle lesions and is not specific for this disease.
3.Measurement of myoglobin
Myoglobin is found only in cardiac muscle and transverse muscle. Most patients with myositis have elevated serum myoglobin, and its fluctuations parallel the disease, and sometimes its changes appear before CK changes, but the specificity is poor.
4. Autoantibody examination
Autoantibodies can be detected in the serum of most patients and these antibodies can be classified as.
① myositis-specific autoantibodies that appear only in inflammatory myopathies.
② autoantibodies that are often found in inflammatory myopathies but are not specific for myositis.
(iii) autoantibodies that appear in syndromes where myositis and other diseases overlap.
For example, anti-rRNP and anti-Sm antibodies can be detected in cases with SLE, anti-Scl-70 antibodies in cases with systemic sclerosis, and anti-SSA and anti-SSB antibodies in cases with dry syndrome. In addition, non-specific antibodies such as anti-myoglobin antibody, rheumatoid factor, anti-myosin antibody, anti-troponin and pro-myosin antibody can also be detected.
5.Myozyme spectrum examination
In the course of the disease, serum enzymes of muscle origin can be increased, and their sensitivity from high to low is creatine kinase (CK), aldolase (ALD), aspartate aminotransferase (AST), alanine aminotransferase (ALT), lactate dehydrogenase (LDH), etc. Carbonic anhydrase U1 is the only isoenzyme present in skeletal muscle, which is increased in polymyositis and other skeletal muscle lesions, and is valuable for the diagnosis of muscle lesions.
6.Electromyography
Electromyography is the insertion of a needle electrode into skeletal muscle, which records, amplifies, and displays the electrical activity of the muscle fibers through an oscilloscope outside the cell.
Typical changes include a triad of signs.
(i) enhanced insertion potential activity, fibrillation potentials and positive sharp waves.
(ii) spontaneous odd high-frequency discharges.
(3) low amplitude, short duration, multi-phase motor unit potential.
7.Histopathological examination
It is best to select the proximal muscles such as quadriceps and deltoid muscles.
(1) The main pathological changes of myositis are myocyte damage, necrosis and inflammation, and the resulting secondary myocyte atrophy, regeneration, hypertrophy, and replacement of muscle tissue by fibrosis and fat. 90% of patients with myositis may have abnormal muscle biopsies, showing damage to muscle fibers, or even necrosis, with varying degrees of regeneration and varying thickness of muscle fibers.
(2) Skin pathological changes are usually
The main manifestations are: mild epidermal thickening or atrophy of the spiny layer, liquefaction and degeneration of the basal cells. The superficial dermis is edematous with scattered or focal lymphocyte (mostly CD4+ T cells), plasma cell and histiocyte infiltration. Fibrin-like material with positive PAS staining was found at the true epidermal junction and around the superficial dermal vessels, and focal mucin accumulation was sometimes seen in the dermis with positive Arsenic blue staining. The subcutaneous fat shows focal lipofuscinosis with mucinous degeneration of adipocytes in the early stages and extensive calcification in the later stages.The pathology of Gottron lesions is characterized by hyperkeratosis and thickening of the spinous layer on top of the above pathological changes.
Diagnosis
The diagnosis is based on symmetrical proximal muscle weakness, pain and tenderness with characteristic skin lesions such as purplish-red edematous spots centered around the orbit, Gottron’s sign and rigid dilated capillary erythema of the nail root crease.
The diagnosis of the disease can be confirmed by the combination of increased serum myoplasmic enzymes and CPK, LDH, AST, ALT and aldolase and, if necessary, electromyographic changes and biopsy of the diseased muscle. It is still adopted by most clinicians.
The table of diagnostic criteria proposed by Bohan and Peter in 1975 is still adopted by most clinicians.
Table Bohan and Peter’s diagnostic criteria for polymyositis and dermatomyositis
1. Progressive weakness of the symmetrical limb girdle and cervical flexor muscles over a period of weeks to months, with possible dysphagia or respiratory muscle involvement
2, skeletal muscle tissue examination shows type I and type II muscle fiber necrosis, phagocytosis, regeneration with basophilic degeneration, muscle membrane cell nuclei become large, nucleoli are obvious, muscle bundle membrane atrophy, fiber size varies, with inflammatory exudate
3, elevated serum skeletal muscle enzymes, such as CK, ALD, AST, ALT and LDH
4, electromyography with triadic changes: i.e. short time frame, low amplitude multiphase motor potentials; frontofacial potentials, positive sharp waves; insertional provocation and bizarre high frequency discharges
5. Characteristic skin changes include: lavender eyelid rash with periorbital edema; Gottron’s sign; scaly redness on the back of the hand, especially the metacarpophalangeal and proximal phalangeal joints.
The rash may also involve the knees, elbows, ankles, face, neck, and upper trunk bilaterally.
Judgment criteria.
polymyositis: confirmed: meeting criteria 1 to 4; rash-like: meeting any 3 of all 1 to 4 criteria
Suspicious: meeting any 2 of all 1 to 4 criteria.
Dermatomyositis: confirmed: meeting any 3 of the criteria in articles 5 and 1 to 4; proposed rash: meeting any 2 of the criteria in articles 5 and 1 to 4.
Suspicious: fulfilling any 1 of the criteria in article 5 and 1 to 4.
Cited in NEnglJMed 292;344,1975
Treatment
The disease is chronic and has a long course. The effectiveness of treatment depends on the type of disease, the treatment plan, and the active cooperation of the patient and family.
1.Glucocorticoids
Clinical experience has proved that glucocorticoids are reliable in the treatment of idiopathic inflammatory myopathies, and are therefore considered the drug of choice for the treatment of polymyositis and dermatomyositis. The lighter ones can be taken orally once in the morning, and the heavier ones are best divided into three oral doses, and once the condition is controlled, it can be changed to one oral dose.
Once the disease is under control, it will be changed to one oral dose. The general course of treatment is not less than 2 years, and finally the drug can be discontinued. If there is no recurrence in 3 years, it is unlikely to recur in the future, and if there is no recurrence in 5 years, it can be basically cured.
2.Immunosuppressant
The commonly used ones are methotrexate and azathioprine. For serious cases, early application of immunosuppressants in combination with glucocorticoids is now advocated.
(1) Methotrexate for adults, once a week, and increase the amount according to the patient’s condition. The dose of methotrexate can be reduced after the disease is stabilized. Methotrexate is maintained in small doses for several months to a year, and premature discontinuation can cause relapse. The combination of methotrexate and glucocorticosteroid can improve muscle strength and muscle enzymes, and reduce the dosage of hormone, thus reducing its side effects, so early application is generally advocated.
(2) Azathioprine combined with glucocorticoids is significantly more effective than hormones alone and can reduce the dose of hormones. However, the drug is slow to take effect, usually after 3 months. The main adverse effects include bone marrow suppression, gastrointestinal reactions and elevated liver enzymes.
(3) Other cyclophosphamide (cyclophosphamide), leflunomide, small doses of cyclophilin A, antimalarials, and immunoglobulin intravenous therapy can play a role in refractory dermatomyositis.
Prognosis
The prognosis of idiopathic inflammatory myopathies continues to improve with the advent of immunosuppressive therapy. In addition to the use of immunosuppressive agents, early diagnosis and treatment, as well as effective control of complications, contribute to an improved prognosis.