Dermatomyositis

Dermatomyositis (DM) is a long-term inflammatory disorder affecting the skin and muscles. It is characterised by a distinct skin rash and progressive muscle weakness. Although it usually manifests in individuals in their 40s and 50s, it can affect people of all ages, with a higher prevalence among women. The condition is chronic and carries potential complications such as calcinosis, lung inflammation, and heart disease.

Signs and Symptoms

Skin

One of the hallmark features of dermatomyositis is the characteristic skin rash. The rash can appear in various forms including a "heliotrope" (purplish or lilac) discolouration around the eyes, often accompanied by swelling. Additionally, rashes may appear on the upper chest and back, known as the "shawl" or "V-sign." Gottron's sign, another common rash, manifests as red or violet, sometimes scaly, slightly raised papules that erupt on finger joints, elbows, knees, or feet.

Gottron's papules on finger joints

Muscles

Muscle weakness is another primary symptom, particularly affecting the proximal muscles such as those in the shoulders and thighs. This progressive weakness makes everyday tasks like standing up, lifting, and climbing stairs increasingly difficult.

Other Symptoms

Around 30% of individuals with DM experience mild joint pain and swelling. Additionally, lung involvement can result in cough and difficulty breathing, and heart involvement may lead to arrhythmias. Gastrointestinal complications, more common in juvenile DM, can include vomiting blood and black tarry bowel movements.

Causes

The exact cause of dermatomyositis remains unknown, although it is hypothesised to result from an autoimmune response possibly triggered by viral infections or cancer. A significant proportion of DM cases are associated with malignancies like ovarian, breast, and lung cancer. Genetic predispositions also play a role, with certain HLA subtypes linked to autoimmune dermatomyositis.

Diagnosis

The diagnosis of dermatomyositis is based on a combination of clinical criteria:

1. Muscle weakness in both thighs or both upper arms.
2. Elevated levels of enzymes found in skeletal muscle detected via blood tests.
3. Electromyography showing characteristic erratic and repetitive high-frequency signals.
4. Muscle biopsy revealing mononuclear white blood cells between muscle cells and abnormal muscle cell degeneration.
5. Presence of typical rashes such as heliotrope rash and Gottron's sign.

Treatment

While there is no cure for dermatomyositis, various treatments can manage and alleviate symptoms. Standard treatment includes corticosteroids, either in pill form or intravenously, and immunosuppressive drugs like azathioprine and methotrexate for those not responding to steroids. Intravenous immunoglobulin is also beneficial. Physical therapy is very important to prevent muscle atrophy and regain strength and range of motion. For skin manifestations, topical corticosteroids and high-protection sunscreen are recommended. In severe cases, surgery may be required to remove painful calcium deposits.

Prognosis

Prior to modern treatments, the prognosis for dermatomyositis was poor. Currently, the condition can be managed effectively with appropriate therapy, although complications involving the heart and lungs remain serious concerns. The cutaneous and muscular symptoms may not always improve concurrently, making treatment challenging.

Epidemiology

Dermatomyositis typically peaks in incidence among individuals aged 40–50, with a higher prevalence in women. The disease affects approximately one to 22 per 100,000 people.

History

The diagnostic criteria for dermatomyositis were established in 1975. The term "amyopathic dermatomyositis" or "DM sine myositis" was coined in 2002 for cases where skin involvement occurs without muscle weakness.

Notable Cases

Several notable individuals have been affected by dermatomyositis, including opera singer Maria Callas, actor Laurence Olivier, and American football player Ricky Bell.

Research

Ongoing research aims to understand the underlying causes and biomarkers of dermatomyositis. Clinical trials are investigating various drugs, including ajulaemic acid, adrenocorticotropic hormone gel, and abatacept, among others.

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Self-assessment MCQs (single best answer)

What is the primary characteristic of dermatomyositis affecting the skin?

Which age group is most commonly affected by dermatomyositis?

Which of the following is NOT a common symptom of dermatomyositis?

What type of rash is characterised by red or violet, slightly raised papules on finger joints, elbows, knees, or feet?

What is a potential complication of dermatomyositis involving the lungs?

Which diagnostic method involves detecting erratic and repetitive high-frequency signals in dermatomyositis?

What is the term used for dermatomyositis cases where skin involvement occurs without muscle weakness?

Which medication is commonly used in the treatment of dermatomyositis?

What is the primary role of physical therapy in managing dermatomyositis?

Which of the following is a potential gastrointestinal complication of juvenile dermatomyositis?