Notalgia paresthetica is the best correct answer for Quiz 649 on Derm101.com, not postinflammatory hyperpigmentation
To the editor
Interactive quizzes are one of the components of Derm101 (www.derm101.com), a website that hosts many educational resources, including the journal Dermatopathology: Practical and Conceptual. At this time, there are more than 800 quizzes on the website.
The authors of Quiz 649 posted the case of a man with two somewhat nummular patches of hyperpigmentation on the upper back (Fig. 1A), which on biopsy showed melanophages around venules of the superficial plexus and in dermal papillae (Fig. 1B).The authors diagnosed the findings in this case as postinflammatory hyperpigmentation. But, on reviewing the images of this quiz, I think that the best diagnosis in this case is notalgia paresthetica.
Fig. 1A and B
Clinical appearance and histopathology of the case presented as quiz number 649. Reproduced from “Interactive Quizzes,” available at: www.derm101.com
First defined by Astvatsaturov in 1934,  notalgia paresthetica (NP) is a primary sensory neuropathy of unknown cause affecting the second to the sixth thoracic spinal nerves.  The characteristic symptom is pruritus on the back occasionally accompanied by pain, paresthesia, or hyperesthesia. The dermatologic finding consists of a well-circumscribed hyperpigmented patch and is thought to be the result of chronic rubbing and scratching that follows the pruritus.  A skin biopsy in NP may show intraepithelial necrotic keratinocytes with melanin and melanophages in the papillary and mid dermis, [2,3] and there is no specific pathological feature. However, some authors observed a significant increase in the number of dermal nerves in a case of notalgia paresthetica. Immunohistochemical examination using a neural marker, S-100, positively stained the nerves. Interestingly, a biopsy from perilesional skin also showed an abnormal nerve proliferation. 
No definite treatment has been found for this disorder and most of the cases reported to date are anecdotal. Topical capsaicin is the option used most widely among dermatologists. Transcutaneous electrical nerve stimulation, gabapentin, oxcarbazepine , botulinum toxin and Ultraviolet B have recently shown promising effects. 
In short, I emphasize the importance of clinicopathological correlation in reaching a more precise diagnosis in this case.