Abstract
Diffuse neurofibromas is an uncommon type of neurofibroma, a benign proliferation of schwann cells of the peripheral nerve sheath, and are most commonly located on the head and neck in children and young adults.1 Rare reports with melanocytic differentiation have been reported in association with NF1.2 We present a case of a 77 year old female who presented for a large “birthmark” on her back that had been previously diagnosed as a neurofibroma and dermal nevus with neurotization by histopathology. However, due to the unique clinical picture and pruritis that was associated with the lesion, the patient was treated with gabapentin and topical steroids. Repeat biopsy revealed scattered spindled cells in the papillary dermis that were diffusely positive for S100 and Melan A consistent with a diffuse neurofibroma with melanocytic differentiation. Van Gieson's stain showed normal dense and delicate elastic fibers. Neurofibromatosis workup is currently pending. A similarly distributed diffuse neurofibroma with melanocytic differentiation was reported along the spine of an 18 year old male with other signs suggestive of neurofibromatosis type I.3 This case highlights the importance of the unique appearance of diffuse neurofibromas, particularly with melanocytic differentiation, and the need for diligence on part of the pathologist as they can appear in similar appearance to anetoderma. 1. Kumar BS, Gopal M, Talwar A, Ramesh M. Diffuse neurofibroma of the scalp presenting as circumscribed alopecic patch. Int J Trichology. 2010 Jan;2(1):60-2. 2. Jože Pižem 1, Kimberly M Nicholson, Jerica Mraz, Victor G Prieto. Melanocytic differentiation is present in a significant proportion of nonpigmented diffuse neurofibromas: a potential diagnostic pitfall. Am J Surg Pathol. . 2013 Aug;37(8):1182-91 3. Friedrich RE, Hagel C. Pigmented (melanotic) diffuse neurofibroma of the back in neurofibromatosis type 1. GMS Interdiscip Plast Reconstr Surg DGPW. 2018 Aug 3;7:Doc04
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