Subcutaneous myospherulosis.

Myospherulosis is an uncommon subcutaneous disorder believed initially to be caused by an endosporulating fungus. Recently investigators have disproved an infectious cause and have shown that the disease represents an alteration in red blood cells, usually produced by petrolatum or lanolin, with an accompanying foreign-body-type response. We report the case of a 57-year-old woman who had received a penicillin injection approximately 40 years before she developed a cystic mass in the right buttock. Examination of the mass revealed the classic histologic findings of this disease.