Determination of the optimum site for diagnostic biopsy for direct immunofluorescence in bullous pemphigoid.

The distributions in deposition of immunoreactants in bullous pemphigoid before and after initiating treatment were investigated. Punch biopsies of skin were performed on each patient from up to five different sites and studied by direct immunofluorescence (DIF). Both groups showed the highest diagnostic yield for DIF from perilesional biopsies, with positivity of 78% from the pretreatment group and 83% from the post-treatment group. The percentage of positive DIF for remaining sites in the pre-treatment group were as follows: 50% lower back, 62% oral mucosa, 70% flexor aspect of forearm, 70% anterior aspect of thigh. The post-treatment group had positive DIF of other sites biopsied as follows: 59% anterior aspect of thigh, 64% flexor aspect of forearm, 68% back. We conclude that a single perilesional biopsy is usually sufficient to provide positive DIF and more than two biopsies is seldom justified as it is unlikely to increase the yield of positive DIF. If it is not possible to obtain a perilesional biopsy, then the anterior aspect of thigh or flexor aspect of forearm is a suitable alternative site. If a second biopsy is considered after initiating treatment, it should be taken from the oral mucosa as this has been shown in a separate study to have a higher rate of positive DIF than uninvolved skin.