Subgroups of canine antinuclear antibodies in relation to laboratory and clinical findings in immune-mediated disease

Background:  Autoimmune system diseases in dogs are commonly referred to as systemic lupus erythematosus (SLE), with a positive antinuclear antibody (ANA) test as a hallmark. In human patients, other systemic ANA-positive diseases with overlapping diagnostic features, referred to as SLE-related diseases, are described.  Objectives:  The objective of this study was to investigate whether different patterns of ANA reactivity represent different systemic autoimmune diseases in dogs. Methods:  Dogs with serum positive for ANA by indirect immunofluorescence (IIF-ANA, titer ≥1:100) (n=56) were identified retrospectively from the patient population at the Department of Small Animal Clinical Sciences, Swedish University of Agricultural Sciences. Dogs were grouped on the basis of ANA staining patterns, and the results of immunodiffusion tests. Clinical, hematologic, serum biochemical, radiologic, and pathologic examinations were described for each group.  Results:  Dogs with a chromosomal–positive, homogeneous ANA staining pattern (n=14) had clinical signs involving multiple organ systems; 8 dogs were anemic. Dogs with a speckled IIF-ANA staining pattern (n=42) primarily had clinical signs of musculoskeletal disorders, fatigue and fever. Precipitating antibodies by immunodiffusion were found only in dogs with a speckled IIF-ANA staining pattern and comprised 4 different subgroups based on antigen specificity. Conclusions: In dogs with homogeneous IIF-ANA staining, SLE is a probable diagnosis because of the diversity of clinical manifestations and autoantibody reactivity against chromosomal antigens. Dogs with a speckled IIF-ANA pattern may have SLE-related diseases, which, in turn, may be correlated with different immunodiffusion subgroups. These syndromes had overlapping clinicopathologic features, as described for human patients.