Dermatomyositis: symptoms, causes and treatment

BAD says the symptoms can include a skin rash that can be itchy, feeling tired and run down, and muscles that feel sore and stiff. The rash usually appears before muscle weakness starts, and sunlight makes it worse. Some people have only a skin rash with no muscle symptoms, while others have both, and these can occur all at once or at different times.

In white skin tones the rash can appear red or purple; in brown and black skin tones it can appear purple or brown. BAD says it is usually more severe on sun-exposed areas, and the skin areas most often affected are around the eyes, over the finger and hand knuckles, the front of the neck (often in a V shape) and the skin around the fingernails.

Myositis UK describes a patchy, dusky red "heliotrope" rash, typically on the hands or face, which on the face is often over the cheeks and about the eyes and can look violet over the eyelids. Muscle weakness most often affects the neck, arms or hips and can make it difficult to lift the arms above the shoulders, climb stairs, get up from sitting or lying, or raise the head. Myositis UK says there may be some trouble swallowing and the voice may become nasal or deeper.

• A rash, often around the eyes, over the knuckles, on the front of the neck and around the fingernails, worse in sunlight.

• Muscle weakness in the neck, arms or hips, which can make stairs and overhead reach hard.

• Sore, stiff or tender muscles, and tiredness.

• Joint pains in some people (Myositis UK).

• Difficulty swallowing or a change in voice in some people (Myositis UK).

The word comes from the Latin for skin (dermis), muscles (myos) and inflammation (itis), BAD explains. Myositis UK describes dermatomyositis as a form of myositis that causes chronic muscle inflammation and weakness, affecting the muscles and connective tissues of the body and sometimes the joints.

Unlike other forms of myositis, Myositis UK says dermatomyositis includes the presence of a red heliotrope rash, and there is also a risk of calcinosis, which is more common in juvenile dermatomyositis, the childhood form.

BAD says treatment options are discussed during clinic appointments and, if different parts of the body are involved, other specialists may also be involved. When the condition is more active, stronger treatments are used; when it is less active, fewer or milder treatments are used.

Corticosteroid tablets lower the response of the immune system. At first a high dose is often used, which is then slowly reduced over several weeks or months. BAD says long-term steroid use can be linked to side effects including stomach irritation, thinning of the bones, diabetes, eye problems and weight gain, and that steroids taken for more than 6 weeks in a row should never be suddenly stopped without talking to a healthcare professional.

Other immune suppressants such as methotrexate, mycophenolate mofetil and azathioprine can be used alone or with steroids. Hydroxychloroquine may help the rash, and sometimes injections such as rituximab or intravenous immunoglobulin are used. Myositis UK says that if there is no response, pulsed intravenous treatment or plasma exchange can be considered, and immunosuppressive drugs are monitored with regular blood tests.

BAD says the cause is unknown but it is believed to be an autoimmune condition. Myositis UK says it is thought to be down to a number of factors, both genetic and environmental, and nothing a particular individual has done themselves. Some feel myositis may be started by a virus or by a combination of a viral infection and a defective immune system.

Myositis UK says it is not inherited, and there is as yet no way to predict who in the general population will be affected.

BAD says that, rarely, dermatomyositis can affect the muscles that line the organs. If the oesophagus is affected, acid can leak out of the stomach (heartburn) and swallowing can be difficult. If the chest wall muscles are affected, it can be hard to breathe deeply, and the lungs can over time become stiff. The heart can rarely be affected, causing palpitations and dizzy spells.

Calcinosis is when calcium is deposited in the skin or muscles, which BAD says look like small firm yellow or white lumps under the skin, sometimes sore. If a lump becomes painful or causes problems, an operation to remove it may be suggested.

BAD says it is important in adults to look for signs of underlying cancer, which occurs in 1 in 4 adults with dermatomyositis and is rare in children. Tell your healthcare professional about unexplained weight loss, a change in bowel habit, bleeding from the back passage, a cough that lasts more than 3 weeks, blood in the urine or night sweats. BAD also advises attending all UK cancer screening appointments, as people with dermatomyositis have a higher risk of cancer.

BAD says healthcare professionals may arrange blood tests, skin biopsies (a small sample of skin looked at under a microscope), and investigations of the muscles including an MRI scan, biopsy or electromyography (EMG), which records electrical activity in the muscles. Other tests to look for causes may also be considered.

Myositis UK says that experienced doctors at a centre familiar with the disease will recognise myositis after a simple examination, and that this is then confirmed by a combination of tests. When muscles are damaged they release enzymes such as creatine kinase (CK) into the blood, which a routine blood sample can detect. Blood tests alone will not confirm myositis but are a useful starting point.

BAD says dermatomyositis cannot be cured, but it often goes away after several years, which is called remission. Myositis UK says many children can expect their disease to go away with appropriate treatment, and that in adults a small percentage get well within two years. For most adults it is a case of living with the disease and understanding as much about the illness as possible so that a nearly normal life can be led, even during periods of increased pain and weakness.

Myositis UK says it is a chronic illness but is rarely fatal. It also says there is always a possibility of the disease returning, and that hormonal changes, particularly in pregnancy, can carry a slight chance of a flare-up, so a medical opinion should be sought before planning pregnancy or when deciding about oral contraception.

BAD says dermatomyositis can get worse after exposure to sunlight. It recommends staying in the shade between 10am and 3pm, wearing sunscreen of SPF 50 or more with the UVA circle logo and/or 4 or 5 UVA stars, applying plenty 15 to 30 minutes before going out and reapplying every 2 hours, and protecting the skin with clothes, a wide-brimmed hat and large ultraviolet protective sunglasses.

Regular exercise can help to reduce problems linked with muscle weakness, says BAD, and Myositis UK says exercise is encouraged even in the early phases, guided by your doctor and physiotherapist.

See a GP if you develop a persistent rash together with muscle weakness, or if you have difficulty lifting your arms or climbing stairs. If you already have dermatomyositis, tell your specialist team promptly about new difficulty swallowing, breathing deeply, palpitations or dizzy spells, since BAD says these can occur when the muscles of the oesophagus, chest wall or heart are affected, and about any of the cancer-related symptoms listed above.

Call 999 or NHS 111 as you would for anyone who has severe difficulty breathing, chest pain or a collapse.

On the NHS, a GP usually refers to dermatology or rheumatology, and further specialists such as neurologists or respiratory physicians may join if other organs are involved. Because it is rare, Myositis UK emphasises that experienced doctors at a centre familiar with the disease are best placed to recognise and confirm it.

Some people also see a private specialist for a faster assessment or second opinion. Immune-suppressing medicines need regular monitoring blood tests, so it helps to be clear who will arrange and review these, and to share results with your NHS team.