Correlation between Histopathological Findings and Results of Direct Immunofluorescence in the Diagnosis of Canine Localized Cutaneous Chronic Lupus Erythematosus

Abstract

Background: Localized chronic cutaneous lupus erythematosus (CCLE), also known as discoid lupus erythematosus, is one of the most prevalent canine autoimmune skin diseases. Histopathology is considered the gold standard for the diagnosis of CCLE and the accuracy of which can be increased by use of direct immunofluorescence (DIF). This study aimed to investigate the fluorescence pattern revealed by DIF in cases of canine localized CCLE and to establish and compare its effectiveness with that obtained from histopathology.

Materials, Methods & Results: Eleven dogs suspicious to localized CCLE, i.e., those animals that presented mucocutaneous lesions as erythema, leucoderma, erosive-ulcerative lesions, and loss of nasal planum architecture and its transition to the haired skin underwent medical physical and laboratory examinations (blood count, platelet count, determination of alanine transaminase, alkaline phosphatase, total protein, serum albumin, urea, creatinine). Only those animals that proved to be normal across both the physical and laboratorial evaluation were included in Group I. Animals belonging to this group were submitted to general anesthesia to biopsy two samples of lesioned skin from nasal planum to histopathologic examination and DIF test. Five dogs with no skin lesions were included in Group II as negative control to the DIF assay. Two samples of no lesioned skin from nasal planum were biopsied to histopathologic and DIF evaluation. The kappa (k) coefficient was used to determine the degree of agreement and reliability of the results of both tests. A P-value < 5% was considered to be statistically significant. In Group I, all animals were normal across both the physical and laboratorial evaluation. A diagnosis of canine CCLE was established in 81.8% (9/11) of the animals based on histopathology analysis. Two dogs, numbers 10 and 11, respectively, had histopathologic findings suggestive of cutaneous leishmaniasis and compatible with canine demodicosis. The DIF assay confirmed the diagnostic of canine CCLE in 100% (11/11) of the cases, including dogs numbers 10 and 11. Direct immunofluorescence positivity for canine localized CCLE was determined by the presence of homogeneous green fluorescence in the basement membrane zone, with IgM and C3 immunoreagents being found at a significantly higher frequency (P = 0.007) than IgA and IgG (P = 0.017 and P = 0.037, respectively). In Group II, no alterations from histopathologic examination and unspecific fluorescence from DIF reaction were shown in all animals belonging to this group. A substantial and significant degree of agreement or reliability (k = 0.738 and P = 0.002, respectively) was established between the results of both tests.

Discussion: In veterinary medicine, there is a lack of studies about DIF around autoimmune dermatoses. This is the first manuscript comparing histopathological and direct immunofluorescence findings in the diagnostic of dogs with localized CCLE. In the present study, the positivity to the DIF assay for canine localized CCLE was established by the presence of green fluorescence of a homogeneous morphologic pattern, especially for IgM and C3, located in the BMZ and cutaneous annexes. Direct immunofluorescence excluded the suspicion of cutaneous leishmaniasis determined by the histopathological findings and confirmed the diagnostic of canine localized CCLE in the dog number 10. Statistically, a substantial degree of agreement and reliability was shown between DIF and histopathology. Therefore, we concluded that the DIF assay is a highly effective and useful complementary examination that improves our ability to diagnose canine CCLE.