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This report describes the clinical, onychoscopic, nail clipping, and histopathologic features of a malignant onychopapilloma. A 71-year-old male presented to our outpatient clinic for a stable, asymptomatic lesion on his left middle finger that had been present for 2 years. Prior nail clipping histopathology showed nail plate thinning with subungual abnormal onychocytes. Clinical examination revealed a 2-mm-wide streak of longitudinal xanthonychia extending to the proximal nail fold, with distal hyperkeratosis and onycholysis. Onychoscopy showed irregular longitudinal nail plate ridging with scattered punctate hemorrhagic foci. An excisional nail unit biopsy demonstrated cellular atypia of the nail bed epithelium, matrix metaplasia, longitudinal abnormal onychocytes, increased Ki-67 staining, and negative HPV immunoperoxidase staining, confirming the diagnosis of malignant onychopapilloma., (© 2024 The Authors. Journal of Cutaneous Pathology published by John Wiley & Sons Ltd.)

Melanoma of the nail apparatus is challenging to diagnose for both dermatologists and dermatopathologists. Misdiagnosis or delayed diagnosis of nail unit melanoma can have fatal consequences and legal ramifications. This review educates dermatopathologists on challenges and traps they should be aware of to avoid misdiagnosis of nail unit melanoma. We present illustrative difficult cases that introduce several themes regarding challenges in the diagnosis of nail unit melanoma: specimens with subtle histopathologic findings, challenges in immunoperoxidase interpretation, and how clinical knowledge and surgical procedural knowledge are mandatory to make the diagnosis. Dermatopathologists will be aware of when and how to suspect nail unit melanoma in unusual circumstances., (© 2023 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.)

We call on dermatologists and dermatopathologists to include nail clipping histopathology as an essential component of the routine evaluation of melanonychia. This manuscript demonstrates a case where an adult woman with broad melanonychia of the right thumbnail declined a nail matrix biopsy, but was amenable to a nail clipping.The nail clipping showed pigmentation, melanocyte remnants, and small cavities in the nail plate. These features have been published previously by our group as a clue to nail unit melanoma within nail clippings.This patient was rapidly triaged for nail matrix biopsy, which demonstrated nail unit melanoma in situ. Every patient with melanonychia can benefit from a nail clipping by examination of the location of the pigmentation within the nail plate for surgical planning, and if melanocyte remnants are detected, the nail clipping also serves as a rapid triage mechanism for nail matrix biopsy to evaluate for nail unit melanoma. Fontana-stained sections will highlight the pigmentation in the nail plate, and its location in the nail plate can easily be described by the dermatopathologist. Nail clippings performed in the setting of clinically apparent melanonychia may show helpful histopathologic findings of pigmented fungi, hemorrhage, external pigmentation, features of other pigmented nail unit tumors, as well as other entities. Nail clipping histopathology can provide extensive information in the evaluation of melanonychia with minimal discomfort for a patient, and little disruption to a physician's clinic flow. With this additional case of a nail unit melanoma diagnosed after initial concern found in a nail clipping, as well as other information in the literature, it is clear that melanocyte remnants found in nail clippings are reliable concerning features related to nail unit melanoma in adults. With knowledge of these histopathologic features in nail clippings and the significance of melanocyte remnants, the dermatopathologist can play a crucial role in the use of a nail clipping as a life-saving diagnostic maneuver. Accordingly, given the potential benefit to patients in this setting, as well as other uses of a nail clipping in the evaluation of melanonychia, we call on dermatologists and dermatopathologists to innovate the routine evaluation of melanonychia through the routine employment of nail clippings for histopathologic evaluation., (© 2022 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.)

Basal cell nevus syndrome (BCNS) is an autosomal dominant condition caused most often by a loss-of-function mutation in the Patched-1 (PTCH1) gene. It is characterized by the development of varied benign and malignant tumors, including numerous cutaneous basal cell carcinomas (BCCs). The PTCH1 gene is integral in hair follicle development and loss of function mutation may lead to BCCs with an infundibulocystic histopathology in BCNS patients. Few studies have described the histopathological features of BCCs in BCNS. The recognition of these histopathologic features by dermatologists, dermatopathologists, and others caring for children will allow earlier and more effective identification of BCNS. We performed a retrospective analysis of 25 BCCs in 11 patients aged 5 to 19 years with BCNS and evaluated the histopathologic features on hematoxylin-eosin-stained sections. Our study found that 80% of BCCs in BCNS patients occurred on the head and neck with 64% of the specimens demonstrating infundibulocystic differentiation. Infundibulocystic differentiation is a common finding in BCCs found in BCNS. The finding of cutaneous neoplasms consistent with BCC with infundibulocystic differentiation in children is common in pediatric patients with BCNS and can be considered to be an early marker of the disorder, prompting further clinical investigation., (© 2020 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.)

Background: Pachyonychia congenita (PC) is a rare autosomal dominant disorder of keratinization mediated by genetic mutations in KRT6A, KRT6B, KRT6C, KRT16, or KRT17. While nail dystrophy in PC has a significant impact on quality of life, the histopathological features of the nail plate in PC have not been previously reported. We report the histopathological features of nail plates provided by 19 patients with genetically confirmed PC., Methods: Nineteen patients with genetically confirmed PC provided a total of 56 nail plates for histopathologic examination. The nail plates were examined for the presence of hyphae, yeast, bacteria, neutrophils, parakeratosis, plasma globules, and hemorrhage. Specimens with onychomycosis (three patients) were excluded from the analysis., Results: No specific histopathological feature was identified in PC nails. Parakeratosis and plasma globules were the most prominent features in both clinically affected and unaffected PC nails. There was a significant association between clinical dystrophy of all 20 nails and KRT6A mutations, and a lack of dystrophy of all 20 nails in KRT6B mutations., Conclusions: Parakeratosis and plasma globules in the absence of other inflammatory disorders should raise PC in the histopathologic differential diagnosis. The presence of onychomycosis in a nail plate does not exclude a diagnosis of PC., (© 2019 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.)

The lunula is the semi-lunar shaped area seen at the proximal aspect of the nail unit. It is the most distal aspect of the nail matrix that can be visualized through the transparent nail plate. The term red lunula describes erythema that partially or completely replaces the normal white color of the lunula. Red lunulae have been associated with a number of dermatologic and systemic conditions. However, the etiology and histopathology of the red lunula have not been characterized. We report a case of red lunulae of the fingernails in an adult male. Histopathologic examination revealed an increased density of benign-appearing and mildly dilated vascular channels present in the superficial papillary dermis of the nail matrix. To our knowledge, this is the first report of distinct pathologic findings seen on histologic examination of a red lunula. The increased vascularity of the lunula seen microscopically correlates with the clinically observed red color. These findings raise the possibility that systemic or local factors are responsible for angiogenesis within the nail unit in disorders associated with the red lunula., (© 2013 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.)

Onychocytic matricoma is a newly described matrical tumor of the nail unit that clinically presents with localized thickening of the nail plate and melanonychia and represents a benign acanthoma of onychocytes. Onychocytic matricoma can be classified according to its histopathologic type (acanthotic, papillomatous or keratogenous with retarded maturation) and pigmentation (pigmented, melanocytic or non-pigmented). However, there are no published reports of non-pigmented onychocytic matricoma. We report a case of hypopigmented onychocytic matricoma that presented with a thickened nail plate, xanthonychia and histopathologic features of acanthosis, prekeratogenous zone and keratogenous zone cells forming pseudosquamous eddies, and minimal pigmentation with Fontana staining. We also provide detailed clinical, intraoperative and histopathologic correlations of this rare tumor. Both clinicians and dermatopathologists should be aware that onychocytic matricoma can present with xanthonychia, thickening of the nail plate and mimic an onychomatricoma., (© 2013 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.)

Onychotillomania represents an unusual dermatosis affecting the nail unit. The term refers to 'neurotic picking at a nail until it is permanently altered'. It can be difficult for dermatologists to diagnose, as typically patients will deny the self-destructive behavior and the clinical features may mimic other inflammatory conditions affecting the nail unit. Aside from the difficulty in establishing the diagnosis clinically, the histopathologic features of onychotillomania are nonspecific. With this limited knowledge, dermatopathologists could have difficulty in correlating the clinical and histopathologic features and determining the correct diagnosis. Establishing the diagnosis is critical, as onychotillomania is sometimes associated with major depression and obsessive-compulsive disorder, and can be a clue to uncovering these debilitating psychiatric disorders. Here we present two cases of onychotillomania and emphasize the clinical-pathological confrontation necessary to secure the diagnosis., (© 2013 John Wiley & Sons A/S. Published by Blackwell Publishing Ltd.)

Localized longitudinal erythronychia describes a solitary red streak limited to a single nail unit. Localized longitudinal erythronychia can be caused by both benign and malignant entities. Most commonly, the cause is a benign process, such as an onychopapilloma. We report a case of an acquired subungual arteriovenous malformation that presented as localized longitudinal erythronychia during pregnancy. To our knowledge, this is the first report of localized longitudinal erythronychia arising from a pregnancy-associated arteriovenous malformation of the nail unit., (Copyright © 2012 John Wiley & Sons A/S.)

Background: Cicatricial forms of alopecia, including lichen planopilaris (LPP) and discoid lupus erythematosus (DLE), may present with overlapping clinical features. In such cases, histopathological examination may provide key information for resolving the differential diagnosis. Optimally, microscopical analysis for alopecia requires both vertical and horizontal sections, and this may necessitate multiple samples. Here, we present what we term the "HoVert" technique, which produces horizontal and vertical sections from a single biopsy. We hypothesize that the HoVert technique should be useful for differentiating DLE from LPP., Methods: A formalin-fixed 4 mm punch scalp biopsy is transected approximately 1 mm below the skin surface to create an epidermal disc and a lower portion. The epidermal disc is bisected and embedded in conventional fashion to obtain vertical sections. The lower portion is serially sectioned and embedded to obtain horizontal sections., Results: The HoVert technique yields vertical sections permitting visualization of the epidermis, the dermal-epidermal junction and perijunctional inflammation. The technique also provides horizontal sections that permit analysis of follicle number, follicle type, perifollicular inflammation and scarring. Evaluation of both vertical and horizontal sections from a single scalp biopsy maximizes the histopathological information obtained and enhances the diagnosis of LPP or DLE in specific cases., Conclusions: We believe that the HoVert technique represents a simple and diagnostically effective tool in differentiating LPP from DLE. It may also be applicable to the assessment of other forms of alopecia., (Copyright © 2011 John Wiley & Sons A/S.)

A perineurioma is a benign peripheral nerve sheath neoplasm thought to be derived from cells of the perineurium, the cellular sheathing of peripheral nerve fascicles. The histological, immunohistochemical (positive for epithelial membrane antigen, collagen type IV, laminin and vimentin but not S-100 protein) and ultrastructural features of a perineurioma form the basis for diagnosis. Two types of perineuriomas are recognized, intraneural and soft tissue (extraneural) forms. Sclerosing perineurioma is considered a variant of the soft tissue perineurioma. In all but one of the reported cases, this subtype presented as a solitary clinical lesion with a predilection for the fingers and palms of young adults. In 2002, Huang and Sung described a 16-year-old boy with one sclerosing perineurioma on each hand. The unusual case presented herein is a 21-year-old woman manifesting more than 30 cutaneous sclerosing perineuriomas on the hands and arms. This case is the most extensive presentation of sclerosing perineuriomas documented to date and extends the clinical presentation spectrum of these lesions.