(BMJ)—A 15-yo boy presented w/ hyperpigmented plaques on his neck x1y. He could not remove them w/ soap and forceful scrubbing. Tests excluded insulin resistance and malignancy. Dermoscopy: large polygonal platelike brown scales in mosaic pattern. What is the dx?
Tinea versicolor
Terra firma forme dermatosis
Epidermal nevus
Acanthosis nigricans
Dermatitis neglecta
You are correct. Dermoscopy findings were suggestive of terra firma forme dermatosis, a benign cause of skin pigmentation that is not uncommon, particularly in young adults. Dx in this pt was confirmed by removal of plaques using isopropyl alcohol wipes. Differential diagnosis includes acanthosis nigricans, dermatitis neglecta, confluent and reticulated papillomatosis, epidermal nevus, tinea versicolor, and seborrheic keratosis. Greater awareness of this easily treatable condition would prevent misdiagnosis and subsequent unnecessary investigations.

BMJ 2017;357:j1860