Antisynthetase syndrome: symptoms, lung involvement, tests and treatment

Myositis is the name for a group of rare conditions in which muscles become inflamed, weak, tired and painful. Antisynthetase syndrome sits within that group but has a distinct pattern. Myositis UK explains that antibodies normally help to keep the body well by attacking bacteria and viruses, whereas autoantibodies mistakenly attack healthy tissue. In this syndrome the target is a set of enzymes called aminoacyl-tRNA synthetases, which are essential for good muscle function.

Arthritis UK notes that some people with this condition have in the past been told incorrectly that they have polymyositis or dermatomyositis. It has some similar symptoms but is now classed as a separate condition.

Because the features can appear in different combinations and at different times, the syndrome is often recognised late. A person may have one feature, or several, and Myositis UK says the syndrome can appear alongside Raynaud's phenomenon, mechanic's hands, polyarthralgia (pain in several joints) and interstitial lung disease.

Myositis UK says the symptoms include all those typical of the conditions mentioned above, which means muscle inflammation, reduced blood flow to the fingers in Raynaud's and dry, cracked skin in mechanic's hands, as well as fever or inflammatory arthritis.

• Muscle weakness, tiredness and pain, often in the shoulders, hips and thighs, which Arthritis UK says can make everyday tasks such as climbing stairs or brushing hair difficult.

• A dry cough or breathlessness from interstitial lung disease. Arthritis UK says a dry cough can occur before skin and muscle symptoms.

• Raynaud's phenomenon, in which the fingers and toes turn white, then blue, and feel very cold, then red and throbbing as they warm.

• Dry, cracked skin on the hands (mechanic's hands).

• Joint pain or inflammatory arthritis, and fever.

See a GP if you have unexplained muscle weakness, a persistent dry cough or breathlessness, or joint pain together with Raynaud's changes or skin changes on the hands. Arthritis UK stresses that the lung involvement can be serious, so symptoms such as a new cough or breathlessness should not be left. If you are very breathless at rest, cannot speak in full sentences, or have chest pain, call 999 or go to A&E.

Arthritis UK notes that myositis can sometimes affect the muscles that carry out tasks such as breathing and swallowing. Difficulty with either needs urgent assessment.

Myositis UK says a blood test screening for myositis-specific autoantibodies can be carried out to test for antisynthetase syndrome. Arthritis UK explains that there is no single test that can show for certain that someone has myositis. A doctor will take a history, examine you and, since symptoms overlap with many conditions, arrange blood tests and other examinations.

Arthritis UK lists blood tests for signs of muscle damage, inflammation and autoantibodies (including ANA, ENA and anti-Jo-1), electromyography (EMG), muscle biopsy and MRI. Because the lungs can be affected, the specialist team will also want to assess the lungs, which is why a new cough or breathlessness is taken seriously.

Some other conditions can look similar to myositis, according to Arthritis UK, including side effects of some medicines such as statins and steroids, thyroid conditions, low vitamin D, infections and other rare muscle conditions, so these are considered before a diagnosis is made.

Myositis UK says antisynthetase syndrome is treated similarly to other types of myositis using steroids, although early and aggressive treatment is particularly important. Because each person is a fairly unique case, other treatment may be used alongside, such as anti-TNF inhibitors for arthritis and immunosuppressants for lung disease.

Myositis UK says the long-term outlook varies with the severity of the condition and its symptoms, that it is considered a chronic illness that often requires long-term treatment, and that people are generally very responsive to steroid and immunosuppressive treatment. If the lungs are affected, the outlook can change somewhat: those with progressive interstitial lung disease may have a worse prognosis because of breathing problems, but in most cases, it says, the disease is not progressive.

Arthritis UK says that even in severe cases myositis usually responds to treatment, although many people need lifelong drug treatment to keep it under control. Monitoring of muscle and lung function, bone health and medicine side effects is part of long-term care.

On the NHS, antisynthetase syndrome is usually looked after by rheumatology, often with respiratory specialists, after referral from a GP. Because it is rare, ask whether your team has experience of myositis or can link with a specialist myositis centre.

Private rheumatologists and chest physicians offer faster appointments or second opinions. Antibody tests, lung scans and treatment are the same in principle, and the main differences are waiting times and continuity. Whoever you see, make sure someone is responsible for monitoring your lungs, as this affects long-term outcome.