The Antinuclear Antibody Test in the Diagnosis of Antisynthetase Syndrome and Other Autoimmune Myopathies.

Abstract

Autoantibodies directed to intracellular macromolecules are a characteristic feature of antinuclear antibody (ANA)-associated rheumatic diseases (AARD) such as systemic lupus erythematosus, systemic sclerosis, mixed connective tissue disease, Sjögren syndrome, and autoimmune inflammatory myopathies (AIM). Some of these autoantibodies are highly specific for the individual AARD and hence are termed disease-specific antibodies, and some are included in the classification and/or diagnostic criteria for these diseases1. In this context, the report by Aggarwal, et al in The Journal 2 is timely and provides insight into the value of screening for anticytoplasmic antibodies (anti-CytAb) as an adjunct to the diagnosis of the antisynthetase syndrome, a subset of AIM3. In their retrospective analysis of 202 patients with antisynthetase syndrome, the anti-CytAb test performed better than the conventional ANA indirect immunofluorescence (IIF) test in identifying antisynthetase syndrome as evidenced by higher sensitivity (72% vs 50%) and specificity (89% vs 6%). Consequently, they indicate that a negative ANA test does not rule out the diagnosis of antisynthetase syndrome or AIM. That a negative ANA does not indicate autoantibody negativity in antisynthetase syndrome or AIM is an important message that may be misunderstood by clinicians. Despite remarkable efforts to standardize ANA nomenclature by the International Consensus on ANA Pattern (ICAP) committee4,5, there is considerable confusion about the term ANA . The efforts of the ICAP were recognized by Aggarwal, et al , but they, as well as some diagnostic laboratories and clinicians, continue to interpret and understand the definition of ANA in a strict sense, meaning only autoantibodies that react with nuclear targets are properly regarded as ANA. The spectrum of autoantibody targets in the nucleus is wide and includes components of the nuclear envelope, nuclear pore complex, nuclear matrix, nucleoplasm, chromatin and chromosomes, nucleolus, and promyelocyte leukemia/coiled bodies … Address correspondence to Dr. M.J. Fritzler, University of Calgary, 3330 Hospital Dr. NW, Calgary, Alberta T2N 4N1, Canada. E-mail: fritzler{at}ucalgary.ca