OVERVIEW

What is dermatomyositis?

Dermatomyositis is a systemic autoimmune disease primarily characterized by muscle and skin damage, often involving multiple organs and systems. The cause of this disease remains unknown but is believed to be associated with autoimmune dysfunction, genetic factors, and viral infections.

How common is dermatomyositis? What is the survival rate?

The incidence of dermatomyositis in China is unclear, while reported rates abroad are approximately 0.6–1 per 10,000, with a higher prevalence in women than in men.

Due to the use of corticosteroids and immunosuppressants, the mortality rate of this disease has significantly decreased compared to the past. Most patients can achieve recovery or remission with treatment. The 5-year and 8-year survival rates reach 80% and 73%, respectively.

Is dermatomyositis hereditary?

Although some studies have reported genetic markers possibly linked to dermatomyositis, familial occurrences of this disease remain rare.

SYMPTOMS

What are the characteristics of muscle lesions in dermatomyositis?

Symmetrical proximal limb muscle weakness (muscles of the arms close to the trunk and shoulders), accompanied by myalgia or muscle tenderness.

When proximal upper limb muscles are affected, difficulty in raising arms, combing hair, or dressing may occur. When proximal lower limb muscles (muscles close to the hips) are involved, it often manifests as difficulty climbing stairs, squatting, or standing up from a seated position.

• Skin lesions: Periorbital rash, presenting as edematous violaceous erythema on the upper eyelids or around the eyes. This rash may also appear on the cheeks, nasal bridge, neck, anterior chest (V-shaped area), and shoulders/back.
• Gottron's papules: Erythematous scaly rash on extensor surfaces of joints. Periungual lesions: Erythema and petechiae at the nail fold. "Mechanic's hands": Hyperkeratosis, fissures, and roughness on the palmar and lateral aspects of fingers, resembling the hands of manual laborers.
• Muscle lesions: Symmetrical proximal limb muscle weakness with myalgia or tenderness. Upper limb involvement causes difficulty raising arms, combing hair, or dressing. Lower limb involvement leads to trouble climbing stairs, squatting, or standing up.
• Lung involvement: The most common pulmonary manifestations are interstitial pneumonia, pulmonary fibrosis, and pleuritis, presenting as chest tightness, shortness of breath, cough, sputum, dyspnea, and cyanosis. Lung involvement significantly impacts prognosis.
• Cardiac involvement: The most common manifestations are arrhythmias and conduction blocks. Severe cases may develop heart failure, a major cause of mortality.
• Other organ involvement: Renal (proteinuria, hematuria, casts), gastrointestinal (dysphagia, choking, epigastric pain), and joint (swelling/pain) manifestations may occur.

What are the characteristics of skin lesions in dermatomyositis?

• Periorbital violaceous erythema (heliotrope rash) on upper eyelids or around eyes, which may extend to cheeks, nasal bridge, neck, anterior chest (V-sign), and shoulders/back (shawl sign).
• Gottron's papules: Erythematous scaly rash on extensor surfaces. Periungual lesions: Erythema and petechiae at nail folds.
• "Mechanic's hands": Hyperkeratosis, fissures, and roughness on palmar/lateral finger surfaces.

Which organ is most frequently affected in dermatomyositis? What are the manifestations?

The lungs are most commonly involved. Interstitial pneumonia, pulmonary fibrosis, and pleuritis are typical pulmonary lesions, presenting as chest tightness, dyspnea, cough, sputum, or cyanosis at any disease stage.

Pulmonary involvement is a major prognostic factor.

Does dermatomyositis affect the heart?

Cardiac involvement occurs in 25-70% of cases, though symptomatic cases are rarer. Arrhythmias and conduction blocks are most common. Severe cases may develop heart failure, a significant cause of death.

What are the clinical manifestations of dermatomyositis?

Muscle and skin lesions are the two primary features. Multiple organs/systems may be affected. Prodromal symptoms like fatigue, anorexia, weight loss, and fever often precede onset.

Is dermatomyositis strongly associated with cancer?

Malignancy occurs in 15-60% of patients—up to 10 times higher than the general population. Cancer screening is crucial for dermatomyositis patients.

What cancers may accompany dermatomyositis?

Associated malignancies vary but commonly include nasopharyngeal, ovarian, breast, melanoma, colon cancers, and non-Hodgkin's lymphoma. Middle-aged/elderly patients are more prone to malignancy comorbidity.

CAUSES

What causes dermatomyositis?

The cause of dermatomyositis is unclear. Research suggests it may be related to viral or toxoplasma infections, drug induction, genetic factors, and autoimmune abnormalities.

DIAGNOSIS

How to determine if muscle strength is normal?

Assessment of muscle weakness severity:

• Grade 0: Complete paralysis, unable to contract or produce movement;
• Grade 1: Slight muscle contraction without movement;
• Grade 2: Limb can move horizontally but cannot lift;
• Grade 3: Limb can lift off the bed (against gravity);
• Grade 4: Can resist resistance;
• Grade 5: Normal muscle strength.

What tests are needed for suspected dermatomyositis?

Routine tests include: complete blood count, erythrocyte sedimentation rate (ESR), C-reactive protein (CRP), myoglobin, complement C3/C4. Special tests include muscle enzymes, electromyography (EMG), muscle biopsy, and autoantibodies.

What are the main muscle enzymes?

Muscle enzymes primarily include creatine phosphokinase (CK), aldolase, alanine aminotransferase (ALT), aspartate aminotransferase (AST), and lactate dehydrogenase (LDH). Among these, CK is the most sensitive for dermatomyositis, and its elevation correlates with the degree of muscle damage.

Is a muscle biopsy always necessary for dermatomyositis?

Muscle biopsy is one of the key diagnostic criteria for dermatomyositis. If dermatomyositis is highly suspected but diagnostic criteria are not fully met, a muscle biopsy is required to confirm the diagnosis.

How is dermatomyositis diagnosed?

The 1975 Bohan criteria are commonly used clinically:

• Symmetric muscle weakness and pain;
• Elevated muscle enzymes;
• Characteristic skin rashes, including heliotrope rash (violaceous edematous erythema on upper eyelids) and Gottron's sign (violaceous keratotic or atrophic erythema over extensor surfaces of joints);
• Myopathic changes on electromyography (EMG);
• Positive muscle biopsy findings, such as muscle fiber degeneration, necrosis, regeneration, vascular proliferation, and inflammatory cell infiltration.

A diagnosis of dermatomyositis is made if the third criterion is met along with any three of the other four criteria.

When is dermatomyositis considered in remission, and can medication be discontinued?

Remission is assessed based on clinical symptoms, muscle strength, and laboratory markers. If the patient has no significant discomfort, normal muscle strength, and normalized markers (e.g., muscle enzymes, ESR, CRP), the condition is generally considered in remission. However, discontinuation of medication should be decided by a specialist after comprehensive evaluation. Even after stopping medication, regular follow-ups are necessary.

What is the difference between dermatomyositis and polymyositis?

Both are idiopathic inflammatory myopathies. Dermatomyositis involves proximal limb, scapular, neck, and pharyngeal muscle inflammation along with characteristic skin rashes, while polymyositis lacks skin manifestations.

How to detect interstitial lung disease (ILD) early in dermatomyositis?

About 30% of dermatomyositis patients develop interstitial lung changes. Acute ILD may present with fever, dry cough, dyspnea, cyanosis, and fine crackles on auscultation. Imaging may show ground-glass, nodular, or reticular opacities, progressing to honeycombing in advanced stages. Some patients have a chronic, insidious course with progressive dyspnea and dry cough. Therefore, all dermatomyositis patients, regardless of respiratory symptoms, should undergo routine chest X-rays for early detection.

Is muscle weakness always present in dermatomyositis?

Muscle weakness can result from various conditions, such as infection-related myopathy, thyroid-associated myopathy, metabolic myopathy, drug-induced myopathy, steroid myopathy, and muscular dystrophy. Dermatomyositis diagnosis requires excluding these factors and adhering to diagnostic criteria.

TREATMENT

Can dermatomyositis be completely cured?

No. Currently, there is no medical method to completely cure dermatomyositis. However, with proper and timely treatment, the condition can be effectively controlled, its progression slowed, and some patients may return to a normal state with fewer relapses.

What are the main treatment methods for dermatomyositis?

The primary treatments are hormone and immunosuppressant therapies, supplemented by other methods, following individualized principles:

• Glucocorticoids: Usually oral prednisone; severe cases may require high-dose methylprednisolone pulse therapy.
• Immunosuppressants: Commonly used include methotrexate, azathioprine, cyclosporine A, cyclophosphamide, and hydroxychloroquine.
• Other therapies: For recurrent and refractory cases, intravenous immunoglobulin injections, biologics (e.g., anti-tumor necrosis factor antibodies, anti-B cell antibodies), and plasma exchange may be used.
  Other adjunctive treatments such as adenosine triphosphate, neostigmine, high-dose vitamin E, vitamin C, and cod liver oil can also aid recovery.

How are hormones generally used in dermatomyositis patients? How long is the treatment?

Hormones remain the first-line treatment for dermatomyositis, with the principles of early, sufficient, and long-term use.

The dosage depends on the condition. Acute cases typically receive intravenous or intramuscular administration, while stable or slowly progressing cases are treated orally. The dose is gradually reduced after the condition is controlled. Efficacy is assessed based on clinical symptoms, muscle strength tests, and serum muscle enzyme levels.

Hormone tapering should not be too rapid, generally not exceeding 1/5 of the original dose each time. The maintenance dose is 5–20 mg/day, and hormone therapy should last at least 2–3 years. Some patients can discontinue use entirely, while others require long-term maintenance.

What are the side effects of long-term hormone use in dermatomyositis patients?

Since dermatomyositis requires long-term, high-dose hormone therapy, careful attention must be paid to preventing and managing side effects.

Common side effects include steroid-induced myopathy, infections, steroid-induced diabetes, gastrointestinal ulcers, steroid-induced psychiatric symptoms, electrolyte imbalances, and osteoporosis.

How can the side effects of hormone use in dermatomyositis patients be prevented and managed?

To reduce hormone side effects, gastric mucosal protectants (to prevent gastrointestinal ulcers) and calcium supplements (with calcitriol or alfacalcidol to prevent osteoporosis) can be used alongside hormone therapy.

For high-dose hormone use, blood potassium levels should be monitored, and potassium supplements (e.g., potassium citrate, Slow-K) should be given if levels are low. Infections should be detected and treated early.

Is dermatomyositis complicated by interstitial lung disease dangerous? How should it be treated?

Dermatomyositis with interstitial lung disease is relatively common, occurring in 5%–65% of cases, with a high mortality rate. It is a significant factor affecting prognosis.

There is no specific treatment for dermatomyositis with interstitial pneumonia. Glucocorticoids combined with immunosuppressants remain the first-line treatment. Early diagnosis and treatment are crucial to reduce mortality.

What factors are related to the prognosis of dermatomyositis?

Before the use of corticosteroids, the mortality rate of dermatomyositis was quite high. With hormone and immunosuppressant therapy, mortality has significantly decreased, and most patients achieve remission or recovery.

The 5-year and 8-year survival rates are 80% and 73%, respectively. Pediatric dermatomyositis has better treatment outcomes.

Poor prognosis is often associated with older age, acute onset, dysphagia, interstitial pneumonia, cardiac involvement, or malignancy. Most deaths result from malignancies, respiratory/circulatory failure, or severe infections.

DIET & LIFESTYLE

What should dermatomyositis patients pay attention to in daily life (diet, daily routine, exercise)?

• Avoid direct sunlight as much as possible. Wear hats, gloves, long-sleeved clothing, or use an umbrella when going out.
• Avoid consuming seafood (fish, shrimp, crab) and other foods that may cause allergies.
• Avoid spicy and irritating foods (such as onions, ginger, garlic, etc.).
• Limit oily foods and avoid overeating.
• Do not smoke or drink alcohol.
• Avoid using cosmetics or hair dyes.
• Ensure adequate sleep, balance work and rest, maintain a positive mood, exercise moderately, and protect against cold, wind, and dampness.
• Attend regular follow-up examinations.

Can dermatomyositis patients have children?

Dermatomyositis patients can have children, but this must be based on the condition being properly controlled. Before pregnancy, patients should consult a rheumatologist to assess their condition and adjust medications and dosages to minimize the impact on the fetus and ensure a safe pregnancy.

What kind of muscle care should dermatomyositis patients receive?

The general principles of care for dermatomyositis are: During the acute phase, patients should rest in bed and perform simple passive joint and muscle exercises twice daily to prevent tissue atrophy, but active exercises are not encouraged.

During the recovery phase, patients can engage in light activities in moderation, avoiding fast movements or excessive range of motion. Gradually increase activity levels based on muscle strength recovery, but avoid overexertion during functional exercises to prevent elevated serum enzyme levels.

Gently massage muscles daily and try to manage daily life independently to slow muscle decline, improve coordination, and delay muscle atrophy. At the same time, avoid direct sunlight exposure or extreme cold to prevent further damage to muscles and skin.

PREVENTION

Can Dermatomyositis Be Prevented?

Although the exact cause and pathogenesis of dermatomyositis remain unclear, it may still be possible to prevent or reduce the onset of dermatomyositis and polymyositis by controlling related risk factors and conditions.

• Control transmission routes of viral and toxoplasma infections to minimize exposure;
• Closely monitor reactions to medications that may induce myopathy or alter muscle enzymes, such as penicillamine and statins, to prevent myopathy;
• For patients with immune deficiencies (e.g., complement deficiency) or a predisposition to rheumatic diseases, avoid factors like vaccinations or medications that may trigger myositis.