Necrotizing infundibular crystalline folliculitis manifesting as a perforating mucinosis: a case report.

: Necrotizing infundibular crystalline folliculitis (NICF) is a rare entity manifesting as waxy folliculocentric papules comprised of filamentous birefringent crystalline deposits. We report a case of NICF in an 85-year-old man, presenting as gritty, cream-colored, and erythematous papules across the midline back. Biopsy demonstrated a pale plug comprised of copious mucin. The diagnostic crystals were initially overlooked because of softening of the paraffin block with 10% ammonia solution, which dissolved the crystals in the initial sections. X-ray microanalysis confirmed the organic nature of the crystals. This is the first report of NICF from North America. Our case highlights the presence of mucin in some cases of NICF and serves as a cautionary tale on the pitfalls of postprocessing artifacts in the histology laboratory.