A previously healthy 22-year-old woman was referred for evaluation of a round plaque in the middle of her forehead. One month earlier, she had volunteered for electroencephalographic studies. The procedure lasted 2 hours, and because the electrode on the forehead was difficult to maintain, the operator vigorously rubbed the skin with an alcohol-ether solution. An erythematous papule was visible under the electrode at the end of the procedure.
Physical examination revealed an oval, very hard plaque measuring 1.5 cm in diameter (Figure 1). The border was slightly elevated and erythematous. The center of the lesion was yellowish and sprinkled with white spots, from which a very firm, whitish material could be extracted. A von Kossa–stained biopsy specimen is shown in Figure 2.
Guillod JF, Hauser C, Ruffieux P, Masouyé I, Harms M. Skin Injury After Electroencephalography. Arch Dermatol. 2002;138(3):405-410. doi:10.1001/archderm.138.3.405