What is this tender, solitary, inflamed nodule?

Case 2:

This tender, solitary, inflamed nodule appeared 6 weeks earlier on the forearm of a 60-year-old man. The lesion has been rapidly growing.

What condition do you suspect?

A.  Inflamed epidermoid cyst.
B.  Keratoacanthoma.
C.  Squamous cell carcinoma.
D.  Infected hair follicle.
E.  Giant molluscum contagiosum.

(Answer on next page.)

An excisional biopsy confirmed the clinical impression of a keratoacanthoma, B. The clinical clue is the central keratotic core in a rapidly growing, dome-shaped nodule. Squamous cell carcinoma is in the differential of keratoacanthoma. A pustular core is characteristic of folliculitis; an epidermoid cyst contains cheese-like material. Molluscum contagiosum lesions do not have a central core.