|Year : 2015 | Volume
| Issue : 2 | Page : 306-308
Pigmented neurofibroma of the skin
Hemalata Mahantappa, Suguna Belur Venugopal, Swati Agarwal
Department of Pathology, Kempegowda Institute of Medical Sciences, Bangalore, Karnataka, India
|Date of Web Publication||16-Dec-2015|
Department of Pathology, Kempegowda Institute of Medical Sciences, Bangalore, Karnataka - 560 070
Source of Support: None, Conflict of Interest: None
Pigmented neurofibroma is a rare variant of neurofibroma commonly associated with neurofibromatosis 1 of diffuse type. Histopathologic examination is essential to differentiate it from other pigmented lesions. We report here a case of pigmented neurofibroma of skin, which was diagnosed after histopathology, histochemistry and immunohistochemistry. We also review the pertinent literature to highlight the differential diagnoses.
Keywords: Neurofibroma, neurofibramatosis, pigmented neurofibroma
|How to cite this article:|
Mahantappa H, Venugopal SB, Agarwal S. Pigmented neurofibroma of the skin
. Arch Med Health Sci 2015;3:306-8
| Introduction|| |
Pigmented neurofibroma (PNF) is a unique subtype of neurofibroma characterized by melanin-laden cells, accounting for less than 1% of all neurofibromas and is mostly seen in patients with neurofibromatosis I.  The pigment is not usually appreciated on gross examination and requires histopathologic examination.  The pigmented cells express both S-100 protein and melanin markers in contrast to surrounding nonpigmented cells, which express S-100 protein only.  Melanin producing cells can be explained on the basis of common origin of melanocytes and Schwann cells from multipotent neural crest cells.
| Case Report|| |
A 48-year-old male presented with a gradually increasing swelling over left gluteal region along with multiple small cutaneous swellings all over body since childhood [Figure 1]a]. He had a family history of similar swellings in his father and sister. He had a large, elevated, soft, slightly tender, nonulcerated mass measuring 11 × 8 × 2 cm over left gluteal region. The patient also had café-au-lait spots [Figure 1]a]. The resected large, rubbery skin covered mass measured 12.5 × 9 × 2 cm. The cut section showed poorly demarcated, solid, gray tan, glistening tumor involving skin and subcutis. The striking feature was the dark brown to blackish streaks of pigmentation [Figure 1]b].
|Figure 1: (a) Diffuse neurofi bromatosis with café-au-lait spots (arrow) (b) A large, solid gray tan, glistening tumor involving skin and subcutis with striking brown to blackish streaks of pigmentation|
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Microscopic examination showed overlying normal epidermis with dermis showing interlacing bundles of loosely arranged spindle-shaped and elongated cells with wavy nuclei within myxocollagenous background. Admixed were dendritic, tadpole-shaped and epithelioid pigmented cells in clusters throughout the tumor. The pigment was brownish black and granular [Figure 2]a]. Also seen was Wagner-Meissner like bodies [Figure 2]b]. Mitotic figures were absent.
|Figure 2: (a) Loosely arranged spindle cells with wavy nuclei and pigmented cells (H and E) × 100× (b) Wagner-Meissner like bodies (H and E) × 100×|
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On histochemical staining, pigment containing cells (Jet Black) [Figure 3]a] were positive for Fontana-Masson silver nitrate reduction and were depigmented when bleached with KMNO 4 [Figure 3]b]. On immunohistochemistry, the tumor cells and pigmented cells were diffusely positive for S100 protein [Figure 4]a], whereas with HMB 45 only the pigmented cells were positive [Figure 4]b].
| Discussion|| |
Our patient was a 48-year-old male with clinical features suggestive of diffuse neurofibromatosis, type 1 [Figure 1]a]. The tumor was ill-defined and rubbery, and involved dermis and subcutis. On cut section, it was gray tan glistening with visible brownish black streaks of pigmentation [Figure 1]b]. 
Schwann cells embedded in fine fibrillary collagenous matrix, small nerve segments and scattered Wegener-Meissner like bodies, a typical component of diffuse type neurofibroma was evident in our case [Figure 2]b].  Melanin laden cells with the unique pattern of distribution in deep dermis and subcutis, accompanying the typical features of neurofibroma [Figure 2]a] is a major helpful tool in distinguishing PNF from other "pigmented tumors."
The PNF needs to be differentiated from other pigmented lesions. The dermatofibrosarcoma protuberans (PDFSP) is an uncommon tumor with a strong predilection for truncal region and has a high local recurrence. , It has uniform fibroblastic cells with prominent storiform pattern and dendritic pigment cells in random distribution, unlike the unique distribution pattern of pigmented cells in PNF. The tumor cells in PDFSP are strongly positive for CD34 and lack diffuse S100 protein immunoreactivity, with S100 expression seen only in the pigmented cells.  In PNF, immunohistochemically, the tumor cells and pigmented cells show diffuse positivity for S100 protein [Figure 4]a]. 
Melanotic Schwannoma is a rare form of pigmented neural tumor linked to an autosomal dominant disorder (Carney's complex) characterized by the presence of myxomas, spotty pigmentation, endocrine overactivity and other abnormalities.  This tumor is deep seated with a predilection for paravertebral region and upper alimentary tract. Macroscopically, it is better "marginated" and exhibits pigmentation and cystic change.  Histologically, tumors show cellular areas alternating with hypocellular areas interspersed with pigmented cells. Pigmented cells are somewhat large and more epithelioid with a large nucleus having open chromatin, and a distinct melanoma like nucleolus.  These features are not evident in PNF.
Cellular blue nevus is an "acquired" melanotic lesion presenting typically in young adults in the lumbosacral and buttock regions.  The tumor has pigmented dendritic cells, and pale staining spindle shaped cells in nodular aggregates. The tumor spreads into the reticular dermis often extending in a dumbbell-shaped configuration into the subcutis. It exhibits more solid, organoid or nested growth pattern in comparison with PNF, and typically lacks abnormal nerve trunks and Wagner-Meissner like bodies. 
The distinction between giant congenital nevus with neuroid features and PNF is less clear. The typical clinical features and microscopic lesion showing junctional activity along with well-defined superficial nevus cells intermixed with a lesser component of diffuse neurofibroma support the diagnosis of congenital neuronevus over that of a PNF. ,
Neuocristic hamartoma is difficult to differentiate from PNF.  Clinically, it presents as an isolated mass with normal skin tone or bluish discoloration, preferentially involving face or scalp. Histologically, neuocristic hamartoma shows complex proliferation of nevomelanocytes, Schwann cells, and pigmented dendritic and spindle cells.
To conclude, PNF is a rare variant of neurofibroma that has often been confused with other pigmented cutaneous lesions. Typical histomorphologic features with unique patterns of melanogenesis, histochemical stains and immunohistochemistry enable diagnosis of PNF accurately and also help differentiate it from other pigmented tumors.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4]