Dermatomyositis

What happens in dermatomyositis

The immune system attacks small blood vessels in the skin and muscles, causing inflammation and damage. It belongs to a group of diseases called idiopathic inflammatory myopathies, along with polymyositis and other forms of myositis. The cause is unknown, but genetics, viral infections, sunlight, medicines and, in adults, cancers may act as triggers.

Symptoms

Skin

The rash often appears before or at the same time as muscle weakness:

• Heliotrope rash: purple or violet discoloration of the upper eyelids, often with swelling
• Gottron papules: red or purple scaly bumps over the knuckles, elbows and knees
• Shawl and V signs: red rash over the shoulders, upper back and front of the chest
• Holster sign: rash on the outer thighs
• Nailfold changes: visible blood vessels and ragged cuticles
• Mechanic's hands: rough, cracked skin on the sides of the fingers
• itching, often marked, and worsening with sun exposure
• scalp scaling and hair thinning

Muscles

• symmetrical weakness of muscles close to the trunk: shoulders, hips, thighs and neck
• difficulty climbing stairs, getting up from a chair, combing hair or lifting objects overhead
• muscle aches or tenderness in some people
• difficulty swallowing (dysphagia) if throat muscles are involved

Some people have the rash without muscle weakness (amyopathic dermatomyositis).

Other organs

• Interstitial lung disease: scarring of the lungs, causing breathlessness and dry cough, particularly with certain antibodies (anti-MDA5, anti-synthetase)
• Joint pain and swelling
• Raynaud's phenomenon: fingers turning white or blue in the cold
• Heart involvement: rhythm problems or heart muscle inflammation (uncommon)
• Calcinosis: hard calcium deposits under the skin, especially in children

Dermatomyositis and cancer

In adults, dermatomyositis is linked to cancer in roughly 15 to 25% of cases, usually diagnosed within 3 years before or after the skin disease starts. Common cancers include ovarian, lung, pancreatic, stomach, colorectal and breast cancers, and lymphoma. Certain antibodies (anti-TIF1-gamma, anti-NXP2) raise the risk. Adults with new dermatomyositis therefore have age-appropriate cancer screening, often including CT scans, and ongoing monitoring. Children with juvenile dermatomyositis do not have an increased cancer risk.

Diagnosis

• Examination of the rash and muscle strength
• Blood tests: muscle enzymes (CK, aldolase), inflammatory markers, and myositis-specific antibodies
• MRI of muscles to show inflammation and guide biopsy
• Electromyography (EMG)
• Muscle or skin biopsy to confirm the diagnosis
• Lung function tests and chest CT for lung involvement
• Swallowing studies, ECG and echocardiogram as needed

Treatment

• Corticosteroids (prednisone) are the first treatment for muscle disease.
• Steroid-sparing medicines such as methotrexate, azathioprine or mycophenolate allow steroid doses to be reduced.
• IV immunoglobulin (IVIG) is effective for dermatomyositis, particularly for difficult skin and muscle disease.
• Rituximab, tacrolimus or cyclophosphamide for severe disease or lung involvement.
• Hydroxychloroquine and topical steroids or tacrolimus for skin disease.
• Sun protection: broad-spectrum sunscreen, protective clothing and avoiding peak sun, since UV light worsens the rash.
• Physical therapy: supervised exercise improves strength and is safe.
• Speech and swallowing therapy for dysphagia.
• Bone protection with calcium, vitamin D and other treatment during long-term steroids.

Outlook

Most people respond to treatment, though it may take months and relapses are common. Some reach remission and can stop medicines. Outcomes are worse with severe lung disease or associated cancer. In children, early aggressive treatment reduces calcinosis and long-term complications.

Frequently asked questions

What does a dermatomyositis rash look like?

Typical signs are a purple or violet rash on the upper eyelids, red or purple scaly bumps over the knuckles, and a red rash on the chest, shoulders and upper back that worsens in sunlight. The rash is often itchy.

What are the first symptoms of dermatomyositis?

Often a skin rash appears first, followed by gradually worsening weakness of the shoulders, hips and thighs, making stairs, standing up and lifting the arms harder. Some people have fatigue, muscle aches or difficulty swallowing.

Is dermatomyositis linked to cancer?

In adults, yes. Up to about a quarter of adults with dermatomyositis have an associated cancer, often found around the time of diagnosis. Cancer screening is recommended for adults with new dermatomyositis. It is not linked to cancer in children.

Can dermatomyositis be cured?

There is no cure, but treatment controls the disease in most people, and some achieve long-term remission and stop medicines. Treating any associated cancer can improve dermatomyositis as well.