How useful is periodic acid-Schiff stain to detect fungi in biopsies from dermatoses of the palms and soles?

Abstract

Periodic acid-Shiff (PAS) stain may help to diagnose fungal infection in biopsies from dermatoses of the palms and soles. It is questionable whether PAS stain should be used routinely or only when tinea is suspected clinically. A total of 195 consecutive punch biopsies of dermatoses from the palms (90) or soles (105) were stained with PAS, regardless of the clinical differential diagnosis. PAS stain showed fungi in the corneal layer of 6 (3%) of the 195 biopsies. Tinea was included in the differential diagnosis in 48 cases, of which 3 (6%) were PAS positive. PAS stain was also positive in 3 (2%) of 147 cases in which tinea was not suspected clinically. All 6 PAS-positive cases were detected in reaction patterns not readily classified as particular diagnostic entities: non-inflammatory keratoderma (2, 11%), chronic lichenified dermatitis (2, 6%), spongiotic psoriasiform dermatitis (1, 2%), and spongiotic dermatitis (1, 4%). There is a low concordance rate between the clinical suspicion and the actual demonstration of fungi by PAS stain in dermatoses of the palms and soles. Routine PAS stains in non-suspected cases have a relatively low yield, which may be improved by limiting the PAS stain to reaction patterns not readily classified as particular diagnostic entities.