Utility of direct immunofluorescence testing for IgA in patients with high and low clinical suspicion for dermatitis herpetiformis.

Abstract

The purpose of this study was to examine the utility of direct immunofluorescence (DIF) testing for the characteristic immunoglobulin A deposits of dermatitis herpetiformis (DH) in patients stratified into high and low clinical suspicion subgroups. We retrospectively analyzed the results of H&E and DIF testing in 77 cases of suspected DH and separated them into high and low clinical suspicion subgroups based on clinical impression at the time of biopsy. The overall sensitivity and specificity of routine (H&E) histologic evaluation were 0.75 and 0.951, respectively. Although there were 13 cases of DH (of 36 total cases) in the high clinical suspicion subgroup, there were only three (of 41 total cases) in the low clinical suspicion subgroup. In the high clinical suspicion subgroup, the positive predictive value (PPV) was 0.9, and the negative predictive value (NPV) was 0.846. Alternatively, the PPV was 0.6 and the NPV was 1.0 for the low clinical suspicion subgroup. Histologic false negatives did occur, but all were in patients within the high clinical suspicion subgroup. It is anticipated that the NPV and PPV will vary due to differing clinical practice characteristics; however, in patients with a low clinical suspicion for DH, these data argue that it may be reasonable to first perform a biopsy for routine histologic evaluation before requesting DIF analysis.