Overview of Polymyositis and Dermatomyositis
Polymyositis and dermatomyositis (PM/DM) is a group of systemic, non-suppurative inflammatory diseases of skeletal muscles, mainly involving the proximal limbs and neck muscles, with clinical manifestations of symmetrical weakness and atrophy of proximal limb girdle muscles, neck and even pharyngeal muscles, and in severe cases leading to myocardial and respiratory muscle involvement and death.PM/DM can also involve a variety of organs with tumors or other connective tissue diseases. DM can also involve a variety of organs, accompanied by tumors or other connective tissue diseases, DM can also be accompanied by specific rashes. There is a tendency to refer to both as idiopathic inflammatory myopathies.
Etiology
The etiology of PM/DM may be related to immunity, infection, genetics, immunization, stress conditions, medications, and a number of diseases that can also lead to the development of this disease. The incidence is 0.5 to 8.4 per million. Pathology is characterized by degeneration of skeletal muscle fibers and interstitial inflammatory changes. It is clinically classified into 7 categories: polymyositis, dermatomyositis, dermatomyositis without myopathy, childhood dermatomyositis, tumor-associated myositis, collagen vascular disease-associated myositis, and inclusion body myositis.
Pathological features of PM: muscle biopsy pathology is an important basis for the diagnosis and differential diagnosis of PM/DM. PM muscle biopsy specimens stained with ordinary hematoxylin-eosin (HE) often show myofibrils of different sizes, degeneration, necrosis and regeneration, as well as inflammatory cell infiltration, which is not specific, and can be seen in a variety of reasons for the muscle lesions, which can not be used to distinguish PM from other myopathies. Immunohistochemistry, myocytes can be seen to express MHCⅠ (histocompatibility complex I) molecules, the infiltrating inflammatory cells are mainly CD8+ T cells, which are multifocally distributed around the myofibers and within the myofibers, this is a more characteristic manifestation of PM, and is also the most important pathological criterion for the diagnosis of PM.
Pathological features of DM: The muscle pathology of DM is characterized by the distribution of inflammation around blood vessels or in and around fascicular septa, but not within the muscle fascicles. The infiltrating inflammatory cells are predominantly B cells and CD4+ T cells, which are distinctly different from PM. However, myofiber expression of MHCⅠ molecules was also significantly upregulated. Intramuscular capillary density was reduced, but the remaining capillary lumen was markedly dilated. Myofiber injury and necrosis usually involved part of the muscle bundles or resulted in perifascicular atrophy. Perifascicular atrophy is a characteristic manifestation of DM, and it has been suggested that if muscle biopsy shows perifascicular atrophy, DM can be diagnosed even if no obvious inflammatory manifestations are seen.
Symptoms
1. Prevalent population
It is more common in females, and the incidence is twice as high as that in males. The peak age groups are 10 to 15 years old and 45 to 60 years old.
2. First symptoms
Most of them are hidden and chronic, and the first symptom is fatigue, tiredness or muscle pressure pain; a few of them are acute and sudden onset.
3. Muscle lesions
Early muscle weakness mainly involves the shoulder girdle muscles and pelvic girdle muscles, and about half of the patients have neck and pharyngeal muscle involvement, especially flexor muscle involvement. The affected muscles have obvious pain, tenderness, activity limitation and muscle weakness. Corresponding manifestations are difficulty in lifting the upper limbs, inability to carry objects, combing hair, lower limb weakness, difficulty in walking, running, climbing stairs, difficulty in lifting the head, difficulty in swallowing, dysphagia, etc. Involvement of respiratory muscles may also cause shortness of breath, dyspnea and even respiratory arrest. Cardiac muscle involvement has panic, discomfort in the precordial area, even stuffy pain, shortness of breath, arrhythmia. However, facial muscles and extraocular muscles are rarely involved.
4. Skin lesions
In DM, 1/4 of the rashes appear at the same time with myositis and 1/2 precede myositis.
(1) Positive rash refers to the dark purple-red macules and papules distributed on the upper eyelids, periorbital area, zygomatic area, “V” shaped area of the neck, shoulders and upper back, which are sensitive to light and may be accompanied by edema: the edematous dark purple-red macules appearing on the periorbital area are located in the upper eyelids near the inner canthus, and the obviously dilated capillaries can be seen when the eyes are closed, and there is occasionally a pinpoint hemorrhage spot on the tip of them. Occasionally there is a pinpoint hemorrhage at its tip. This type of rash usually appears and disappears early with myositis, and is related to the activity of the disease.
(2) Gottron’s sign is located on the interphalangeal joints, metacarpophalangeal joints, metatarsophalangeal joints, elbow, knee extensors, and the medial side of the ankle joints. It is a (purplish)-red maculopapular rash with clear borders, accompanied by oedema and scaling, and may be accompanied by atrophy of the skin and hypochromia, which is not related to the disease activity.
(3) Heterochromatosis-like skin rash is mainly distributed on the forehead, upper chest and other exposed areas, with multiple keratotic papules, accompanied by blotchy dark brown hyperpigmentation, capillary dilation, mild skin atrophy and hypopigmentation, not related to disease activity. There may also be nail root folds, capillary dilatation erythema, nail folds may have irregular thickening, and sometimes there may be manifestations such as hard, tight skin on the extremities.
(4) Malignant erythema On the basis of DM lesions, a kind of chronic, fiery red, diffuse erythema is found on the head and face, which is drunken-like appearance, accompanied by more dark brown, grayish-brown pigmented spots and a large number of coiled and dendritic dilated capillaries, and the discoloration of the slides is often suggestive of malignant tumors.
(5) Other skin manifestations Raynaud’s phenomenon, photosensitivity, skin vasculitis manifestations, subcutaneous nodules, purpura and urticaria.
(5) Arthralgia/arthritis
The degree of arthralgia/arthritis is mild, symmetric, non-invasive, and mainly in the small joints of the fingers. Some patients have joint deformity caused by muscle contracture.
6. Digestive tract involvement
Dysphagia, esophageal and gastric emptying abnormalities may be present. In children, DM may present with gastrointestinal ulcers, bleeding and ischemic necrosis caused by vasculitis.
7. Pulmonary lesions
There are mainly acute and chronic interstitial lesions, but also aspiration pneumonia caused by respiratory muscle weakness.
8. Heart involvement
The manifestations are congestive heart failure and severe arrhythmia.
9. Kidney
Myoglobinuria, hematuria, proteinuria and tubular urine, etc. Most of the kidneys have normal function.
10. Other manifestations
Subcutaneous calcium deposits are seen in chronic, pediatric DM patients, and severe cases may cause disability. There may also be systemic manifestations, such as fever, mostly low to moderate fever, if there is high fever, it suggests that there may be infection; fatigue, weight loss, lymph node enlargement can also occur, and some have thrombocytopenia, peripheral neuritis, epilepsy and arachnoid hemorrhage.
Examination
1. Enzymology
Urinary creatine, blood and urine myoglobin are elevated; serum muscle enzymes such as CK, ALT, AST, ALD (aldolase), LDH can be elevated, and their activities are parallel to the disease activity. Among them, CK (mainly CK-MM) is mainly elevated.
2. Autoantibodies
Antibodies against various muscle components (myoglobin, myosin, troponin, promyosin, etc.), ANA (spot type is the most common), anti-tRNA synthetase antibodies such as anti-Jo-1 (anti-synthetase syndrome) antibodies, anti-mi-2 antibodies, anti-PM-Scl antibodies, anti-U1-RNP and SSA antibodies may be positive, and there may also be RF positivity.
3. Immunology
ESR, CRP, γ-GT, IgG, IgM, IgA, IC may be increased, C3, C4 decreased, blood test may have mild anemia and increased leukocytes and eosinophils, a few have proteinuria.
4. Electromyography (EMG)
EMG three-phase changes are: ① insertional excitation, spontaneous muscle fibrillation, high sharp positive waves; ② complex polyphasic, short-time potentials during random contraction; ③ paroxysmal recurrent high-frequency potentials.
5. Pathologic examination
Muscle pathology: there are different degeneration, necrosis and regeneration of muscle fiber bundles, and inflammatory cell infiltration around blood vessels. There may also be atrophy of muscle bundles. Skin pathology: edematous dark purple erythema shows epidermal atrophy, liquefaction and degeneration of basal cells, and infiltration of lymphocytes in the superficial layer of the dermis; Gottron’s papules have hyperkeratosis of the epidermis, hypertrophy of the stratum spinosum, and papillomatous proliferation.
Diagnosis
Bohan and Peter’s diagnostic criteria (1975): ① Symmetric weakness of the limb-girdle and anterior cervical flexors, lasting weeks to months, with or without weakness of the esophageal or respiratory muscles. ② Muscle biopsy showing inflammatory muscle changes. ③ Elevated serum skeletal muscle muscle enzymes. ④ Electromyographic changes. ⑤ Skin manifestations of tophi rash, Gottron’s sign, and peri-nail congestive rash.
Possession of the first 3-4 items (DM plus rash) confirms the diagnosis of PM; possession of 2 of the first 4 items (DM plus rash) is likely to be PM; possession of 1 of the first 4 items (DM plus rash) is likely to be PM.
Differential Diagnosis
A variety of diseases can cause skin and muscle lesions. If there is a typical rash and muscle weakness, DM is generally not difficult to diagnose, the most easily misdiagnosed clinically is PM, which needs to be differentiated from a variety of types of diseases: PM should be differentiated from the main types of muscle include: infection-related myopathy, IBM, thyroid-related myopathy, metabolic myopathy, drug myopathy, hormonal myopathy, myotonic dystrophy, eosinophilic myositis, and tumor-related myopathy. associated myopathies, among others.
Treatment
1. General treatment
Pay attention to rest, especially in the acute stage, absolute bed rest; do not overstress, exertion, regular life; regulate the diet structure, eat more vitamins, sugar and protein-rich and low-fat food; strengthen the psychological treatment, adhere to the regular medication and follow up. DM patients should pay attention to sunscreen. In addition, nursing staff should pay attention to help patients turn over and pat their backs to prevent them from developing pneumonia and pressure sores. Find the cause of the disease, treat the symptoms, treat the original disease, and eliminate the tumor if there is a tumor. Actively prevent and treat various infections.
2.Drug treatment
(1) Glucocorticoid is the first choice of drugs for this disease. Medium and small doses are enough for mild cases, while heavy cases (with respiratory muscle or important organ involvement) need to be treated with large doses of hormone for maintenance or shock therapy. Generally, muscle strength and muscle enzymes will improve after 2 weeks, and dysphagia caused by interstitial lung disease, arthropathy, pharyngeal and upper esophageal lesions can also be relieved. After the muscle strength and muscle enzymes are restored, the hormones are gradually and slowly reduced, and the drug is usually discontinued after 2 to 3 years of maintenance. Whether the initial dose of hormone is appropriate and whether the long-term treatment is adequate is the key to the treatment of this disease. In addition, non-fluoride-containing hormones such as prednisone and hydrocortisone should be chosen to avoid drug-induced myositis.
(2) Immunosuppressant Glucocorticosteroids with poor efficacy, intolerance or complications and relapse when hormone dosage is reduced should be added with immunosuppressant, which can improve the symptoms, reduce the dosage of hormone and reduce complications.
(3) Other treatments Immunomodulators such as transfer factor, thymic peptide, intravenous immunoglobulin, etc.; plasma exchange can be used if necessary. Chinese medicine and traditional Chinese medicine can also be given as adjunctive treatment.