Onychopapilloma presenting as longitudinal leukonychia

To the Editor: Onychopapilloma is an uncommon benign nail neoplasm characterized histologically by distal subungal hyperkeratosis and nail matrix metaplasia of the nail bed with marked papillomatosis. The majority of cases present clinically as localized longitudinal erythronychia. We report a case of onychopapilloma presenting as localized longitudinal leukonychia. A 50-year-old woman was referred for the evaluation of dystrophy of the right third fingernail. The nail plate had split distally for several years. Her medical history was noncontributory. The physical examination revealed a 1-mm wide band of longitudinal leukonychia with a slight longitudinal ridge on the right third fingernail. No erythronychia was present. Distally, there was a V-shaped notch and split, with a keratotic 1-mm papule at the hyponychium (Fig 1). The other nails were normal. Lateral nail plate curl avulsion exposed a longitudinal ridge extending from the midmatrix onto the nail bed. A longitudinal biopsy from matrix to hyponychium was performed. On histologic examination, the nail bed exhibited slender, elongated, and hyperplastic rete ridges with underlying fibrosis and thickening of the fibrovascular dermal stroma. Upper nail bed keratinocytes were large and exhibited ample pink cytoplasm similar to the nail matrix keratogenous zone. Hyperkeratosis was seen at the hyponychium (Fig 2). A periodic acid–Schiff test did not reveal fungal elements. These findings were consistent with the diagnosis of onychopapilloma.Fig 2A, Acanthosis of the nail bed epithelium with elongated rete ridges. B, Thickened fibrovascular stroma with incidental subungual inclusion cyst. C, Nail bed with large eosinophilic keratinocytes indicative of matrix metaplasia. D, Hyperkeratosis at the hyponychium. (A-D, Hematoxylin–eosin stain; original magnifications: A, ×4; B, ×4; C, ×40; D, ×4.).View Large Image Figure ViewerDownload Hi-res image Download (PPT) Onychopapilloma was first reported in 1995 by Baran and Perrin,1Baran R. Perrin C. Localized multinucleate distal subungual keratosis.Br J Dermatol. 1995; 133: 77-82Crossref PubMed Scopus (50) Google Scholar who described four cases of “distal subungual keratosis with multinucleate cells.” The term “onychopapilloma” was later coined in 2000 when the authors reported a second series of 14 cases with similar clinical and histopathologic features.2Baran R. Perrin C. Longitudinal erythronychia with distal subungual keratosis: onychopapilloma of the nail bed and Bowen's disease.Br J Dermatol. 2000; 143: 132-135Crossref PubMed Scopus (99) Google Scholar Key among these features were the upper cell layers in the nail bed epithelium exhibiting abundant eosinophilic cytoplasm resembling the nail matrix keratogenous zone, and was thought to indicate matrix metaplasia of the nail bed epithelium. Additional findings included acanthosis and papillomatosis of the distal nail bed epithelium. Multinucleated cells were found variably. In both series, all lesions presented as either longitudinal erythronychia or longitudinal bands of splinter hemorrhages, several of which were associated with distal onycholysis. Other occurrences of suspected onychopapilloma have been reported, including one case representing solitary nail bed lichen planus, and also in the spectrum of localized longitudinal erythronychia.3de Berker D. Perrin C. Baran R. Localized longitudinal erythronychia: diagnostic significance and physical explanation.Arch Dermatol. 2004; 140: 1253-1257Crossref PubMed Scopus (64) Google Scholar In addition to onychopapilloma, the differential diagnosis for localized longitudinal erythronychia includes Bowen disease,2Baran R. Perrin C. Longitudinal erythronychia with distal subungual keratosis: onychopapilloma of the nail bed and Bowen's disease.Br J Dermatol. 2000; 143: 132-135Crossref PubMed Scopus (99) Google Scholar, 3de Berker D. Perrin C. Baran R. Localized longitudinal erythronychia: diagnostic significance and physical explanation.Arch Dermatol. 2004; 140: 1253-1257Crossref PubMed Scopus (64) Google Scholar and histologic investigation is often warranted. This case is particularly unique because, to our knowledge, it is the first reported variant of onychopapilloma presenting as longitudinal leukonychia. Although punctuate and transverse leukonychia have been reported frequently and are commonly related to trauma, little has been described about the differential diagnosis for longitudinal leukonychia. The scant literature has attributed cases of longitudinal leukonychia to either mounds of horny cells in the nail bed4Baran R. Dawber R.P.R. Richert B. Physical signs.in: Baran R. Dawber R.P.R. de Berker D. Hankeke E. Tosti A. Diseases of the nails and their management. 3rd ed. Blackwell Science Ltd., Oxford2001: 48-103Crossref Scopus (16) Google Scholar or parakeratotic hyperplasia of the nail bed epithelium with or without abnormal keratinization of the nail plate.5Higashi N. Sugai T. Tamamoto T. Leukonychia striata longitudinalis.Arch Dermatol. 1971; 104: 192-196Crossref PubMed Scopus (14) Google Scholar In this instance, we suspect that the leukonychia can be attributed to the metaplasia of nail bed epithelium causing altered light refraction and fibrosis of the nail bed stroma.