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Author: Dr Priyam Sobarun, Dermatology Registrar, 2014.
Antisynthetase syndrome is a rare inflammatory muscle disease related to dermatomyositis and polymyositis.
The hallmark of antisynthetase syndrome is the presence of serum autoantibodies directed against aminoacyl-tRNA synthetases. These are cellular enzymes involved in protein synthesis. Antisynthetase antibodies include Jo-1, PL-7, PL-12, OJ, EJ, KS, Wa, YRS and Zo. Anti-Jo-1 antibodies are the most commonly detected in antisynthetase syndrome.
Antisynthetase syndrome is 2–3 times more common in women than in men.
The cause of antisynthetase syndrome is unknown. It is classified as a chronic autoimmune disease.
The main clinical features of antisynthetase syndrome are:
Antisynthetase syndrome can present with a variety of clinical features and these may vary over time.
Symptoms of antisynthetase syndrome
Some case studies have reported various malignancies occurring within 6–12 months of the diagnosis of antisynthetase syndrome. Age-appropriate screening is therefore recommended, as for dermatomyositis.
The clinical presentation is a clue to the diagnosis of antisynthetase syndrome. Special investigations help to support the diagnosis. These may include the following depending on the clinical context:
Glucocorticosteroids are the mainstay of treatment for antisynthetase syndrome and are often required for several months or years. Prednisone is initially given at high doses (1 mg/kg/day) for 4–6 weeks to achieve disease control, then tapered slowly over 9–12 months to the lowest effective dose to maintain remission. In more severe cases, pulsed intravenous (IV) methylprednisolone for 3-5 days may be necessary.
Improvement in muscle strength can take several weeks or months. Symptomatic improvement is a more reliable indicator of response to treatment than serum CK levels.
Prophylactic treatment is recommended against steroid-induced osteoporosis and certain fungus infections such as Pneumocystis jirovecii. Need for immunisations should be assessed prior to commencing therapy.
Other immunosuppressive medications may be used, such as:
Physical therapy and rehabilitation should start early to prevent muscle deconditioning and to improve weakness.
Patients with antisynthetase syndrome respond well to systemic steroids and/or immunosuppressive agents if they only have muscle involvement.
If lungs are involved, the severity and type of lung injury determine the prognosis. Older age at onset (>60 years), presence of malignancy, and negative ANA antibody test confer a worse prognosis.
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