<prompt> Which of the following antibodies is specific for myositis:Anti - Jo-1Anti - Scl-70Anti - SmAnti- ku  <response>: Answer is AAnti-Jo-1: Anti-Jo-1 Antibodies Antibodies to histidyl - tRNA are the most common and most clinically assayed Myositis Specific Antibodies MSA Myositis Specific Antibodies MSA Myositis Specific antibodies are autoantibodies, usually directed against intracellular ribonucleoproteins that are involved in protein translation. The three best described Myositis Specific Antibodies MSA are Anti-Jo-1directed to t-RNA histidyl-synthetase, Anti-Mi2 and Anti - SRP Anti Signal Recognition Paicle The sensitivity of these antibodies is believed to be low Specific MSA are however associated with ceain clinical features and prognosis. M.S.A Association Clinical Features Prognosis Anti-Jo-I Polymyositis Relatively Acute Onset Moderate 30 sensitive Predicts deforming ahritis, Reynauds Phenomenon and Pulmonary fibrosis Moderate Response to therapy but persistent disease Anti-Mi-2 Dermatomyositis Relatively Acute Onset Good 5 sensitive Predicts classical dermatomyositis rash V sign, Shawl sign and cuticular over growth Good response to therapy and good prognosis Anti- SRP Polymyositis Very Acute onset Poor Dermatomyositis 5 sensitive Predicts severe weakness, palpitations no rash Poor response to therapy and poor prognosis 