Investigation of antinuclear antibodies in canine atopic dermatitis

Serum samples from 40 atopic dogs and 20 healthy dogs were assayed for antinuclear antibodies (ANA) using a human epithelial cell line (HEp-2) and standard indirect immunofluorescent methods. Samples from the atopic dogs were grouped according to the presence (n = 28) or absence (n = 12) of facial lesions at any moment during the follow-up period. Positive ANA titres were found in 10 of the 40 atopic dogs analysed (25%) whereas samples from the control group were negative. Eight atopic dogs with facial lesions had a positive titre (28.57%) in contrast with atopic dogs without facial lesions where two positive samples (16.67%) were found; however, the differences were statistically not significant. Endpoint titres were low (1/40), only two samples yielded a 1/80 positive titre and one sample had a 1/320 titre, all of them from the facial lesions group. Response to immunotherapy was classified as positive only in four of the 10 ANA-positive patients (40%) compared with a response rate of 73% (22 of 30) in the ANA-negative atopic dogs. However, a Fisher's exact test showed a two-sided P-value of 0.122 which was considered statistically not significant. The overall response rate to immunotherapy for all atopic dogs was 65% (26 of 40). In conclusion, the prevalence of ANA is higher in atopic than in healthy dogs, especially if facial lesions are present. Although a clinically significant pathogenic contribution is not probable, this higher prevalence should be taken into account in the differential diagnosis of canine autoimmune dermatitis.