Antisynthetase syndrome is a chronic autoimmune condition that affects the muscles and various other parts of the body. The signs and symptoms can vary but may include muscle inflammation (myositis), polyarthritis (inflammation of many joints), interstitial lung disease, thickening and cracking of the hands, and Raynaud phenomenon. The exact underlying cause is unknown; however, the production of autoantibodies (antibodies that attack normal cells) that attack certain enzymes in the body called 'aminoacyl-tRNA synthetases' appears to be linked to the cause of the syndrome. These autoantibodies may arise after viral infections, or patients may have a genetic predisposition. Treatment is based on the signs and symptoms present in each person but may include corticosteroids, immunosuppressive medications, and/or physical therapy.

• Fever
• Loss of appetite
• Weight loss
• Muscle inflammation (myositis)
• Inflammation of multiple joints (polyarthritis)
• Interstitial lung disease (ILD) causing shortness of breath, coughing, and/or dysphagia
• Mechanic's hands (thickened skin of tips and margins of the fingers)
• Raynaud phenomenon

Some studies suggest that affected people may be at an increased risk for various types of cancer, as well. Some symptoms of the disease seem to vary according to the autoantibody involved in the disease. Myopathy occurs more often in patients with anti-Jo-1 or anti-PL-7; anti-Jo-1 is related to severe arthritis and "mechanic's hand", while anti-PL-12 with higher rates of Raynaud phenomenon; and anti-PL-7, anti-PL-12, anti-KS, and anti-OJ with cases of ILD.

Aminoacyl-tRNA synthase (ARS) autoantibodies associated with ASS include anti-Jo1 (anti-histidyl), anti-EJ (anti-glycyl), anti-OJ (anti-isoleucyl), anti-PL7 (anti-threonyl), anti-PL12 (anti-alanyl), anti-SC (anti-lysil), anti-KS (anti-asparaginyl), anti-JS (anti-glutaminyl), anti-Ha or anti-YRS (anti-threonyl), anti-tryptophanyl, and anti-Zo (anti-phenylalanyl) autoantibodies, with anti-Jo1 being the most common.

• Blood tests to evaluate levels of muscle enzymes such as creatine kinase and aldolase
• Laboratory tests to look for the presence of autoantibodies associated with antisynthetase syndrome
• High resolution computed tomography (HRCT) of the lungs
• Electromyography (EMG)
• Muscle biopsy
• Pulmonary function testing
• Magnetic resonance imaging (MRI) of affected muscles
• Evaluation of swallowing difficulties and aspiration risk
• Lung biopsy

Not all patients with antisynthetase antibodies or even those classified as having the antisynthetase syndrome have all manifestations of this syndrome. Diagnosis is considered in patients with an antisynthetase antibody plus two major criteria or one major criterion and two minor criteria:

Major criteria:

1. Interstitial lung disease (not explained by environmental, occupational, medication exposure, and not related to any other base disease)

2. Polymyositis or dermatomyositis

Minor criteria:

1. Arthritis

2. Raynaud phenomenon

3. Mechanic's hand

Corticosteroids are typically the first-line of treatment and may be required for several months or years. These medications are often given orally; however, in severe cases, intravenous methylprednisolone may be prescribe initially. Immunosuppressive medications may also be recommended, especially in people with severe muscle weakness or symptomatic interstitial lung disease. According to recent studies, Rituximab is the medication option when patients with lung disease do not respond well to other treatments. Physical therapy is often necessary to improve weakness, reduce further muscle wasting from disuse, and prevent muscle contractures.

Several studies have shown that the following factors may be associated with a worse prognosis:

• Older age at onset (greater than 60 years)
• Severity and extension of lung disease: The more severe and extensive lung involvement the worse the prognosis
• Presence of malignancy (cancer)
• Delay in diagnosis and treatment: Prognosis is better when the patients are treated early
• Having a negative Jo1 antibody test: Several studies have shown that Jo1 status seems to be associated with prognosis, suggesting that non-Jo1 patients (patients who have other anti-ARS antibodies, that are non-Jo1) have worse survival rates than Jo1 patients.