The cure for boredom

As a histopathologist, one’s experience with daily casework has remarkable consistency yet can vary considerably. Before initiating a day’s work as a dermatopathologist, one can expect certain trends to occur. With certainty, one can expect to encounter solar keratosis, solar lentigo, basal cell carcinoma, and spongiotic dermatitis. Tumors or proliferations of melanocytes will also undoubtedly be in the mix. Whether removed because of irritation, for cosmesis, or due to genuine clinical concern for the possibility of malignancy, a day at the microscope always includes the evaluation of conventional melanocytic nevi, flat compound and junctional (Clark/dysplastic) nevi, and melanomas. Joy in a given day can be contributed by the unexpected return of old friends. Microscopically distinctive disorders such as chondrodermatitis nodularis helicis, warty dyskeratoma, erythema nodosum, or Meyerson’s nevus may appear under the scope periodically and provoke an intellectual smile. Numerous other disorders may present as a distinct rarity and trigger scholarly amusement. A few days ago, a granular cell basal cell carcinoma crossed my stage. Its appearance charmed me, and at the moment it also sunk in that considerable time had passed since encountering a similar tumor. A vagary in the practice of any dermatopathologist is the occasional clustering of similar unusual cases, phenomena, or morphologies. One might come across adenosquamous carcinoma twice in a week and then wait months for another encounter. Typically this is written off as coincidence, although one wonders if bias triggered by recent visual experiences could be a cofactor. Does seeing a particular cellular morphology, such as cytoplasmic vacuoles, in a given tumor make one more attuned to that morphology, and thus more prone to making a particular type of diagnosis in the cases that follow? Sometimes encountering a peculiarity, remembering it, and the finding it again and again can serve as the basis for advancing the field. For example, when first encountering perineural involvement in association with an adnexal tumor such as trichoepithelioma,1,2 one might not recognize its significance. Indeed, because neurotropism is ingrained in all of us as a manifestation of malignancy, encountering benign tumor wrapped around a nerve might provoke an interpreter to render a false diagnosis of cancer! However, after encountering a phenomenon repeatedly, such as the identification of perineural extension in seven conventional examples of desmoplastic trichoepithelioma,1 it becomes clear that a novel observation has arrived. In a similar vein, a recent oddity in my practice is that I am encountering the juxtaposition of melanocytic and neural differentiation quite routinely. Of course, we all encounter ‘‘neurotization’’ of melanocytic nevi on a daily basis, but I am alluding to something different. It started with the recognition of perineuriomatous differentiation within melanocytic nevi,3 which I suspect is a relatively common phenomenon, but it has moved beyond that. Recognizing similarities and overlap between melanocytes and the nerve sheath is nothing new, of course, as it has been clear for decades that both are neurocristic in origin.3,4 The observation that melanocytes share key light microscopic and immunophenotypic characteristics with peripheral nerves comes as no surprise to any serious student of cutaneous histomorphology or cutaneous embryology. It has even been postulated that the stem cell reservoir for repopulation of cutaneous melanocytes may reside in superficial peripheral nerves.5 In short, it is widely known and well documented that melanocytes and nerves are closely intertwined. Three recent cases have been illustrative of new aspects of the expansive interplay between melanocytes and the nerve sheath. The first represented a non-pigmented nodular proliferation of plump cells with avid HMB-45 and Melan-A immunopositivity from the leg of a young woman.6 (Editor’s note: the case will be presented in full in a forthcoming issue of the JCP.) Because of its size,