This 43-year-old man presented with several erythematous papules on his penis. The clinician was concerned for bowenoid papulosis. While consistent with bowenoid papulosis, this is not something we diagnose on histology, as the findings are identical to other forms of squamous cell carcinoma in situ. We sign these out as "full-thickness dysplasia". In this case, there was an incidental finding of amyloid, possibly representing macular or lichen amyloidosis. There was no clinical evidence for systemic amyloidosis. This amyloid material stained with Congo Red and keratin immunohistochemical stains. The etiology is unknown, but likely due to chronic irritation.
This high power view is a Congo Red stain. The stain highlights this amorphous material, supporting the presence of amyloid, or beta-pleated sheets.