Artifactual Stratum Corneum Calcification of the Beagle Dog Tongue

Examination of H&E-stained tongue samples from a 26-week intravenous infusion study of Beagle dogs, utilizing a compound with no recognized effect on mineral metabolism, exhibited superficial stratum corneum calcification in both treated and control animals. This resulted in the search for possible causes of the finding to help clarify confounding issues. Retrospective examination of 11 studies performed before the signal case indicated that the problem existed in the testing facility but was not recognized. Prior to 2008, this finding was not observed, perhaps indicating the requirement for a change in procedures or suppliers. Based on the hypothesis that the calcium salts were deposited from bone during processing, a series of tests was performed by fixing tongue and femur along with different tissues, processed routinely to slide, and stained with H&E and von Kossa stains. We conclude that the presence of superficial stratum corneum calcification of the tongue in dogs demonstrated in toxicology studies is an artifactual change related to the processing of tissues, specifically the fixation of tongue in the same container as bone and stomach. This change should not be confused with compound-related effects, even when the incidence varies between controls and treated animals.