This biopsy came from the dorsal foot of an immunocompetent adult patient who awoke with painful vesicles on the hands, feet, and mouth. The clinical differential diagnosis was hand, foot, and mouth disease/coxsackie virus infection vs. bullous lichen planus. The patient had a prior biopsy 6 months ago that looked more like PLEVA than lichen planus and looked nothing like this current biopsy.
The necrotic vesicle is very small, a few millimeters in diameter. One might think of herpes virus infection at low power, although I usually see more inflammation and necrosis with herpes and usually a larger lesion. The infiltrate in this biopsy is more lymphocytic, rather than neutrophilic. It lacks the 3 M’s of multinucleation, molding of nuclei, and margination of the nuclear chromatin that you seen in herpes, although within the necrosis the cells can look multinucleated. Immunohistochemistry for herpes may be of help in such cases.
Hand-foot-mouth disease occurs in summer and early fall. It is commonly associated with coxsackievirus A16 but could be associated with other viruses like enterovirus 71. This is the second biopsied case of HFMD I’ve seen in a week. I’m expecting the third any day now.