The white, round spots seen in this lesion were entirely consistent with SK and were not misinterpreted (choice “a”). Since melanoma is not known to display this type of spot, choice “b” is also incorrect. Biopsy reports are occasionally wrong, of course, but the diagnosis of melanoma is fraught with such serious implications that the call is not made if specific criteria are not met. These include specific stains for that diagnosis, histologic findings, and the concurrence of multiple observers, so it is unlikely that the histologic diagnosis is incorrect (choice “d”).
This leaves the correct answer, choice “c,” discussed below.
There is truly no law saying that two lesions can’t appear in the same location—and as this case illustrates, it definitely happens. Had we performed additional biopsies, no doubt features of SK would have been seen in corroboration of the dermatoscopic findings.
This case also emphasizes another useful principle: Pay just as much attention to the owner as to the lesion itself. This patient was quite fair and sun-damaged, so any odd lesion he developed would be suspect, let alone one that looked like this.
One final thing to be learned from this case is that as useful as dermatoscopes can be, they still must take a backseat to common sense.