Dermatomyositis (DM) is a rare, chronic, autoimmune disorder characterized by both inflammatory muscle disease and distinct cutaneous manifestations. Although it can affect individuals of all ages, sexes, and ethnicities, the disease demonstrates a higher prevalence in adult females. DM is often triggered by an immune-mediated process in genetically predisposed individuals, which may be exacerbated by environmental factors such as infections, drugs, or malignancies. Additionally, DM frequently coexists with other connective tissue diseases like systemic lupus erythematosus, rheumatoid arthritis, scleroderma, Sjogren’s syndrome, and mixed connective tissue disease.

Pathophysiology and Risk Factors

While the exact etiology of dermatomyositis remains unknown, the disease is believed to result from autoimmune dysregulation, where the immune system attacks the skin and muscles. In some cases, the condition may be associated with underlying malignancies, particularly in older adults. The frequency of cancer in adults with DM ranges between 10% and 50%, with an increased risk for cancers such as ovarian, breast, lung, gastric, and other female genital cancers. This relationship underscores the need for thorough oncologic screening in adult patients diagnosed with DM. In pediatric cases, calcinosis, or the deposition of calcium salts under the skin, can develop, leading to firm, yellow-to-white lumps, especially in the knuckles and elbows.

Clinical Manifestations

Dermatomyositis often presents with non-specific systemic symptoms such as fatigue, weakness, and muscle pain. The skin manifestations may precede or accompany the muscle symptoms. One of the most notable dermatologic features is the heliotrope rash, a purple discoloration affecting the eyelids, which is characteristic of the condition. Gottron’s papules, which are scaly, erythematous lesions over the knuckles, are another hallmark of DM. Other skin findings include poikiloderma, a condition marked by thin, atrophic skin, visible blood vessels, and hyperpigmented spots in sun-exposed areas such as the face, neck, shoulders, and upper chest.

Muscle Involvement

Muscle weakness, particularly in the proximal muscles (e.g., hips, shoulders, upper arms, and neck), is a hallmark of dermatomyositis and can result in significant functional impairment. This symmetric weakness can progress to involve all muscle groups, causing difficulties with daily tasks such as standing up from a sitting position, climbing stairs, or combing hair. Tenderness may be present in affected muscles, particularly during advanced stages of the disease. In approximately 15-30% of cases, interstitial lung disease or pulmonary involvement may develop, complicating the clinical course.

Diagnosis

The diagnosis of dermatomyositis is clinical, supported by characteristic skin findings such as the heliotrope rash and Gottron’s papules. A skin biopsy can confirm the diagnosis by revealing specific histopathological features, including perifascicular atrophy and perivascular inflammation. Additionally, blood tests measuring creatine kinase and aldolase levels help assess the extent of muscle damage. The presence of autoantibodies such as anti-Jo-1, anti-Mi-2, and anti-SRP can support the diagnosis and offer insights into disease prognosis. Imaging techniques such as MRI and electromyography are valuable tools in detecting muscle inflammation and evaluating muscle electrical activity. Muscle biopsy remains the gold standard for confirming the diagnosis, especially in cases where the clinical presentation is unclear or other inflammatory myopathies need to be excluded.

Management

While dermatomyositis has no known cure, treatment is aimed at controlling inflammation, improving muscle strength, and managing skin manifestations. Corticosteroids such as prednisone are the mainstay of therapy and are effective in reducing muscle inflammation and improving skin symptoms. The dosage of corticosteroids is usually tapered based on the patient’s response to treatment and the severity of the disease. In patients with refractory or severe disease, immunosuppressive agents like methotrexate, azathioprine, cyclophosphamide, and mycophenolate mofetil may be used either alone or in combination with corticosteroids to suppress the immune response.

In cases of non-responding dermatomyositis or those with complications such as lung involvement, intravenous immunoglobulin therapy may be considered. Sun protection is also critical in the management of DM, as sun exposure exacerbates skin damage. Patients are advised to use broad-spectrum sunscreens, sun-protective clothing, and hats to prevent further skin deterioration. Additionally, physical therapy plays a crucial role in maintaining or improving muscle strength and flexibility, enhancing quality of life and functional capacity.

Conclusion

Dermatomyositis is a complex autoimmune disorder that primarily affects the skin and muscles. Although the exact etiology remains unclear, it is often triggered by environmental factors in genetically predisposed individuals. The disease presents with characteristic cutaneous and muscular symptoms, and its diagnosis relies on a combination of clinical features, laboratory tests, and biopsy findings. While there is no cure for dermatomyositis, modern therapies, including corticosteroids, immunosuppressive drugs, and physical therapy, can significantly improve symptoms and quality of life. Ongoing research is essential to uncover more effective treatments and better understanding of the disease pathogenesis.

References

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