The clinical characteristics of Polymyositis (PM) and Dermatomyositis (DM) are non-purulent inflammatory myopathies of skeletal muscles, PM refers to no skin damage, such as myositis with rash is called DM. It can also involve multiple systems and organs, and can be accompanied by tumors. The cause of this disease is unknown, but it is an autoimmune disease. The pathogenesis is related to viral infections, immune abnormalities, genetics and tumors. MicroRNA virus-like structures have been found in myocytes, and tubular inclusions resembling paramyxovirus nucleosomes have been found in skin and muscle vessel walls and endothelial cells by electron microscopy. Cell-mediated immune responses have been found to play an important role in muscle. Deposits of IgM, IgG, and C3 are found in the skeletal bone blood vessels, with a higher rate of positivity especially in the childhood type of dermatomyositis. The phenomenon of correlation between malignancy and dermatomyositis suggests that tumors can cause myositis, which may be the result of an immune response against common antigens of muscle and tumor. PM/DM is not uncommon in our country, but the incidence is not clear. The incidence in the United States is 5 per million people, with a female prevalence and a male to female ratio of 1:2. The disease can occur at any age and has a bimodal onset, with a peak in children aged 5 to 14 years and in adults aged 45 to 60 years. In 1975, Bohan and Peter classified PM/DM into five categories: 1) primary polymyositis; 2) primary dermatomyositis; 3) PM/DM combined with tumors; 4) childhood PM or DM; and 5) PM or DM with other connective tissue diseases (overlapping syndrome). 1982, Witaker added two categories to this classification, namely inclusion body myositis and others (nodular, focal, and periorbital). In 1982, Witaker added two categories to this classification, namely inclusion body myositis and others (nodular, focal and periorbital myositis; eosinophilic myositis; granulomatous myositis; proliferative myositis). Clinical manifestations] The disease is insidious in adults and has a more rapid onset in children. Acute infection may be the precursor or cause of the disease. The early symptoms are proximal muscle weakness or rash, general malaise, fever, malaise, weight loss, etc. 1, muscle The disease involves the transverse muscles and is characterized clinically by weakness of the proximal muscles, often with symmetrical damage, with muscle swelling and pressure pain in the early stages and muscle atrophy in the late stages. Most patients do not have distal muscle involvement. (1) Muscle weakness: almost all patients present with varying degrees of muscle weakness. Myasthenia gravis may occur suddenly and continue to progress for weeks to months or more. The clinical manifestations are related to the site of the involved muscles. Shoulder girdle muscle and proximal upper extremity muscle weakness: inability to lift the upper extremity flat or up, comb the hair, or put on the head. Weakness of pelvic girdle muscles and thigh muscles: inability or difficulty to lift legs, inability to get into a car, go upstairs, sit down or get up after squatting. The cervical flexors can be severely involved: difficulty in raising the head in a flat position, and the head is often tilted back. Weakness of the laryngeal muscles causes difficulty in articulation and hoarseness. The involvement of the transverse muscle of the upper pharynx and esophagus causes difficulty in swallowing, choking and coughing when drinking water, and liquid flowing out of the nostrils. Weak and dilated peristalsis of the lower esophagus and small intestine causes acid reflux, esophagitis, dysphagia, epigastric distention and absorption disorders. It is difficult to differentiate from the symptoms of progressive systemic sclerosis. Involvement of the thoracic muscles and diaphragm presents with superficial breathing, dyspnea, and causes acute respiratory insufficiency. Judgment of the degree of muscle weakness: Grade 0: complete paralysis; Grade 1: muscles can contract slightly and cannot produce movement; Grade 2: limbs can move in planes but cannot be lifted; Grade 3: limbs can be lifted off the bed (resistance to geocentric attraction); Grade 4: resistance can be resisted; Grade 5: normal muscle strength. (2) Myalgia There may be muscle swelling in the early stage of the disease, and about 25% of patients have pain or pressure pain. 2. Skin DM has skin damage in addition to muscle symptoms. Most of them are slightly dark erythema. The skin lesions are slightly commercialized out of the skin surface, the surface is smooth or scaly. The lesions can often fade completely, but may also remain brownish pigmentation, atrophy, scars or white spots. Calcification of the skin may also occur, especially in children. Generalized calcinosis is seen especially in untreated or inadequately treated patients. The skin lesions are characterized by (1) periorbital edema with a dark purple-red rash, seen in 60%-80% of patients with DM; (2) Gottron’s sign, a rash located on the extensor surfaces of joints, mostly at the elbow, metacarpophalangeal, proximal interphalangeal joints, but also on the skin of the knee and inner ankle, manifesting as erythema with scaling, skin atrophy, and hypopigmentation. (3) Diffuse erythematous rash in the “V” area of the neck and upper chest, and also on the forehead, cheeks, preauricular area, cervical triangle, shoulders and back. (4) Vasculitis manifestations such as dark purple congested rash on the base and both sides of the nails, finger ulcers, infarct foci on the nail edges, Raynaud’s phenomenon, reticular bruises, and polymorphic erythema. Chronic cases sometimes show multiple keratotic papules, patchy hyperpigmentation, capillary dilation, mild skin atrophy and pigment loss, called vascular atrophic heterochromia DM.(5) Some patients have keratosis, cracks in the skin of the outer palm surface of both hands, rough and flaky skin, similar to the hands of skilled workers, called “skilled” hands. This is especially common in anti-Jo-1 antibody PM/DM. The first two types of skin lesions above are characteristic for the diagnosis of DM. The extent of the lesions may not parallel the extent of the muscle lesions, and in a few patients the rash appears before the muscle weakness. About 7% of patients have a typical rash, but there is no muscle weakness, myopathy, or normal muscle enzyme profile, which is called “dermatomyositis without myopathy”. 3. Joints Arthralgia and arthritis are seen in about 20% of patients and are asymmetric, often affecting the finger joints. 4.Gastrointestinal tract 10%-30% of patients have dysphagia and food reflux, which is caused by the involvement of upper esophagus and pharyngeal muscles, and barium retention in the pear-shaped fossa of the esophagus can be seen in barium swallowing radiography. 5, lung About 30% of patients have interstitial lung changes. The clinical manifestations of acute interstitial pneumonia and acute interstitial pulmonary fibrosis include fever, dry cough, dyspnea, cyanosis, and fine wet rales in the lungs, and hairy, granular, nodular, and reticular shadows on X-ray in the acute stage. In the advanced stage of pulmonary fibrosis X-ray examination can be seen. Honeycomb or whorl shadows. Some patients have a chronic course with an insidious clinical presentation and a slow onset of progressive dyspnea with dry cough. Pulmonary function is measured as restrictive ventilatory dysfunction and diffusion dysfunction. Rapid development of pulmonary fibrosis is one of the important causes of death in this disease. Only 1/3 of patients have myocardial involvement, with inflammatory cell infiltration, interstitial edema and degeneration, focal necrosis, ventricular hypertrophy, rhythm disturbances, congestive heart failure, and pericarditis. About 30% of electrocardiograms and echocardiograms show abnormalities, with ST-segment and T-wave abnormalities being the most common, followed by conduction block, atrial fibrillation, pre-term contractions, and small to moderate pericardial effusions. 7. Kidney Renal lesions are rare. Very few patients with fulminant onset may develop myoglobinuria and acute renal failure due to rhabdomyolysis. A few patients with PM/DM may have focal proliferative glomerulonephritis, but most patients have normal renal function. 8, calcium deposits Most often seen in patients with chronic dermatomyositis, especially in children, calcium deposits in soft tissue, if calcium deposits in the subcutaneous, ulceration in the deposits can have lime-like flow out. Most of the tumors are solid tumors such as: lung cancer, gastric cancer, breast cancer, nasopharyngeal cancer and lymphoma. The inflammatory symptoms of the muscle can be improved after the tumor is removed. 10, other connective tissue diseases About 20% of patients can be accompanied by other connective tissue diseases, such as systemic sclerosis, systemic lupus erythematosus, dry syndrome, polyarteritis nodosa, etc. PM and DM coexist with other connective tissue diseases and meet their respective diagnostic criteria, called overlap syndrome. 11, PM/DM in children Children have more DM than PM, about 10 times to 20 times, with rapid onset, muscle edema, obvious pain, retinal vasculitis, and often accompanied by gastrointestinal bleeding, mucosal necrosis, vomiting blood or black stool, and even perforation and need for surgery. Later in the disease, subcutaneous, muscle calcium deposits, muscle atrophy. 12, inclusion body myositis (inclusion body myositis) This disease is mostly seen in men over 50 years old, with insidious onset, lesions involving the proximal muscle groups of the limbs, but also the distal muscle groups. Unlike PM, muscle weakness and myasthenia are poorly symmetrical, finger flexors and foot drop are common, and myalgia and muscle pressure are rare. Myoenzymes are normal and respond poorly to hormone therapy. The pathology is characterized by eosinophilic inclusion bodies found in the cytoplasm and nucleus of myocytes, and electron microscopy shows tubular and filamentous inclusion bodies in the cytoplasm and nucleus. The diagnosis of PM/DM is not difficult for typical cases, but atypical cases need to be differentiated from other causes of myopathy, such as motor neuron disease, myasthenia gravis, progressive myotonic dystrophy, rheumatic polymyalgia, etc. Diagnostic points of PM/DM: 1. ( 2 ) Typical skin rash and distribution. In some patients, the rash only appears in the inner canthus of the eye and on both sides of the nasal bridge at the beginning of the disease, or there is a typical rash without muscle weakness should be noted. ( 3 ) Fever is not uncommon in PM/DM patients, especially in those with concurrent lung damage. 2, auxiliary tests ( 1 ) serum muscle enzymes: the majority of patients in a certain stage of the disease process can appear increased muscle enzyme activity, as one of the important serum indicators for the diagnosis of the disease. Creatine enzymes include creatine kinase (CK), aldolase (ALD), lactate dehydrogenase (LDH), portal aminotransferase (AST), carbonic anhydrase III and so on. CK is the most sensitive of the above-mentioned myoenzymes. An increase in myoenzymatic activity indicates recent muscle damage and an increase in myocyte membrane permeability, so the level of myoenzymes has a parallel relationship with the change in myositis. It can be used as an indicator for diagnosis, efficacy monitoring and prognosis evaluation. The elevation of myosin often precedes the clinical manifestations by several weeks, and myosin is no longer released after advanced myasthenia. In patients with chronic myositis and extensive muscle atrophy, myosin levels can be normal even in the active phase. CK has 3 isoenzymes: CK-MM (mostly from skeletal muscle and to a lesser extent from cardiac muscle); CK-MB (mainly from cardiac muscle and rarely from skeletal muscle); and CK-BB (mainly from brain and smooth muscle). CK-MM activity accounts for 95-98% of the total CK activity. PM/DM is mainly dominated by alterations in CK-MM. Carbonic anhydrase III is the only isoenzyme present in skeletal muscle and is elevated in skeletal muscle lesions. However, it is not routinely detected. Other myoenzymes derived from other tissues and organs at the same time are not as helpful as CK in the diagnosis of PM and DM.(2) Myoglobin measurement Myoglobin is only found in cardiac and skeletal muscle, and can be elevated when there is muscle damage, inflammation, and strenuous exercise. Sometimes it can precede CK.(3) Autoantibodies ①Anti-nuclear antibody (ANA): the positive rate in PM/DM is 20%-30%, which is not specific for the diagnosis of myositis. ② Anti-Jo-1 antibody: It is a marker antibody for the diagnosis of PM/DM, with a positive rate of 25%, and up to 60% in patients with combined interstitial lung lesions. Patients with anti-Jo-1 positive PM often present clinically with anti-synthetase antibody syndrome: muscle weakness, fever, interstitial pneumonia, arthritis, Raynaud’s sign, and “mechanic’s hand”. (4) Electromyography Almost all patients can have EMG abnormalities, which manifest as myogenic damage, i.e., fibrillation waves, positive sharp waves, insertion provocation and high-frequency discharge during muscle relaxation; short-time low voltage polyphasic motor potentials during mild contraction, and interference phase during maximal contraction. (5) muscle biopsy Take the proximal muscles of the damaged limb such as deltoid and quadriceps, muscles with pressure pain and moderate weakness are good to send for examination, and the EMG insertion should be avoided. Myositis is often focally distributed and requires multi-site sampling if necessary to improve positive results. Muscle pathological changes: ① Inflammatory cells (lymphocytes, macrophages, plasma cells mainly) infiltrate around the interstitium and blood vessels of muscle fibers. (ii) Myofiber degeneration necrosis and regeneration, manifested by muscle bundle size, fiber necrosis, regenerated muscle fibers basophilic, with large vacuolated nuclei and obvious nucleoli. (iii) Myofibrillar atrophy was characterized by the most obvious periphery of the muscle bundles. The skin pathological changes are not specific. 3, Diagnostic criteria for PM and DM Diagnostic criteria proposed by Bohan and Peter (1975): (1) symmetric proximal muscle weakness with or without dysphagia and respiratory muscle weakness; (2) elevated serum enzyme profile, especially elevated CK; (3) abnormal electromyography; (4) abnormal muscle biopsy; (5) characteristic skin damage. With the above (1), (2), (3), (4) can confirm the diagnosis of PM, with three of the above (1)-(4) may be PM, with only two for suspected PM. with (5), plus three or four can confirm the diagnosis of DM; Article (5), plus two may be DM, Article (5), plus one for suspected DM. 4, the disease needs to be differentiated from the following diseases (1) motor nerve Source disease: myasthenia gravis starts from the distal limb, progressive muscle atrophy, no myalgia, and neurogenic damage on electromyography. (2) Myasthenia gravis: generalized diffuse muscle weakness, significant decrease in muscle strength after progressive persistent or repeated exercise, normal serum muscle enzymes and muscle biopsy, positive serum anti-acetylcholine receptor (AchR) antibody, neostigmine test helps to diagnose. (3) Myotonic dystrophy: muscle weakness starting from the distal limb, no myalgia, and genetic family history. (4) Rheumatic polymyalgia: the age of onset is often older than 50 years, manifested by pain, weakness and stiffness of proximal muscle groups such as neck, scapular girdle and pelvic girdle, blood sedimentation may be increased, muscle enzymes, electromyography and muscle biopsy are normal, and glucocorticoid therapy has significant efficacy. (5) Infectious myopathy: myopathy is associated with viral, bacterial, and parasitic infections and manifests as myalgia and muscle weakness after infection. (6) endocrine abnormalities due to myopathy: for example, periodic paralysis caused by hyperthyroidism, with weakness of both lower limbs, symmetrical, with myalgia, aggravated by activity, hypokalemia during episodes, muscle symptoms relieved by potassium supplementation; hypothyroidism due to myopathy, mainly manifested as muscle weakness, but also progressive muscle atrophy, commonly chewing muscles, sternocleidomastoid muscles, quadriceps muscles and muscles of the hand, muscle contraction after Flaccidity is prolonged, and relaxation is slow after clenching the fist. (7) Metabolic myopathy: PM should also be differentiated from myopathies such as mitochondrial disease, disorders of purine metabolism, disorders of lipid metabolism and disorders of carbohydrate metabolism. (8) Others: It should also be distinguished from drug-induced myopathy, such as myopathy caused by long-term use of high-dose hormones, myalgia starting from the lower extremities, normal muscle enzymes; myasthenia gravis caused by long-term use of penicillamine, etc.; ethanol, chloroquine (hydroxychloroquine), cocaine, colchicine, etc. can cause toxic myopathy. Treatment plan and principles】 1, general treatment In the acute stage, bed rest is required, passive limb exercise to prevent muscle atrophy, appropriate exercise after symptom control, give a high-calorie, high-protein diet, avoid infection. 2, drug treatment (1) glucocorticoid: is the first choice of drugs for this disease, the usual dose of prednisone 1, 5-2mg/kg/d, morning once orally, severe cases can be divided into oral doses, most patients in 6-12 weeks after treatment muscle enzymes decreased, close to normal. The dose should be reduced when muscle strength is clearly recovered and myoenzymes are normalized. The dose should be reduced slowly (generally about 1 year), to a maintenance amount of 5-10mg/d and then continue to use the drug for more than 2 years, in the process of reducing the dose, if the disease recurrence should be promptly added immunosuppressant, for the rapid development of the disease or respiratory muscle weakness, dyspnea, dysphagia, available methylprednisolone 0, 5-1g/d intravenous shock treatment, for 3 days, changed to 60mg/d oral, and then according to the symptoms and The dosage is then gradually reduced according to the symptoms and myozyme levels. It should be noted that infection should be closely observed during the course of hormone administration, and anti-infective drugs should be added when necessary. (2) Immunosuppressants: Immunosuppressants should be added promptly for patients with recurrent and severe disease. The combined application of hormone and immunosuppressant can improve the efficacy, reduce the dosage of hormone and avoid adverse reactions in time. (1) Methotrexate (MTX): commonly used dose amount is 10-15mg/week, orally or with saline 20ml, slowly pushed intravenously, if there is no adverse reaction, the dosage can be increased according to the condition, but the maximum dose does not exceed 30mg/week, gradually reduce the dosage after the condition is stabilized, and maintain treatment for several months to more than 1 year. The adverse effects of MTX include increased liver enzymes, bone marrow suppression, hematocrit, and stomatitis. Blood tests and liver and kidney functions should be checked regularly during the drug administration. Adverse reactions include bone marrow suppression, hematocrit and liver enzyme increase. Blood tests should be performed every 1-2 weeks at the beginning of the drug, and then every 1-3 months for routine blood tests and liver function. Cyclophosphamide (CYC): Those who cannot tolerate or are not satisfied with MTX can switch to CYC 50-100mg/d orally, and for severe cases, 0,8-1g plus 100ml of saline and intravenous shock treatment. Adverse reactions mainly include bone marrow suppression, hematocrit, hemorrhagic cystitis, ovarian toxicity, and induction of malignancy. During the drug administration, blood routine and liver function should be monitored. 3. Patients with combined malignant tumor, if the tumor is removed, myelitis symptoms can be naturally relieved. Prognosis】 Early diagnosis, reasonable treatment, the disease can be satisfactory long-term remission, patients can engage in normal work, study, and enjoy the same quality of life as ordinary people. This is especially true for pediatric patients. Adult patients can die from severe progressive muscle weakness, dysphagia, malnutrition, and respiratory failure due to aspiration pneumonia or recurrent lung infections. Those with polymyositis complicated by cardiac or pulmonary pathology are often severely ill and poorly treated. Children usually die from vasculitis of the intestines. The prognosis of patients with myositis complicated by malignancy is generally dependent on the prognosis of the malignancy.