Congenital subungual melanocytic nevus with a pseudo-Hutchinson sign
Published Web Locationhttps://doi.org/10.5070/D32qx5931b
Congenital subungual melanocytic nevus with a pseudo-Hutchinson sign1. Department of Dermatology, Tufts Medical Center, Boston, Massachusetts
Ari M Goldminz1 BA, Deon Wolpowitz2 MD PhD, Alice B Gottlieb1 MD PhD, Michael S Krathen3 MD
Dermatology Online Journal 19 (4): 8
2. Department of Dermatology, Boston University Medical Center, Boston, Massachusetts
3. Department of Dermatology, Cutaneous Oncology, Stanford University School of Medicine, Stanford, California
We describe a 29-year-old woman with congenital melanonychia striata and compound nevus of the right first digit. There was extension of the hyperpigmentation onto the proximal nail fold, even beyond the borders established by the band of melanonychia striata. A dermal plaque with irregular borders and variegated pigmentation was also present over the distal digit extending from the pigmented region of the hyponychium. A limited number of biopsy proven congenital subungual melanocytic nevi have been reported in the literature. Interestingly, we found that the majority of these cases present with longitudinal melanonychia in association with periungual hyperpigmentation, constituting a pseudo-Hutchinson sign. Currently studies evaluating the diagnostic test characteristics of Hutchinson sign are lacking. While Hutchinson sign is traditionally considered a worrisome feature it is certainly not pathognomonic and a malignant cause should not be assumed without thorough assessment.
A 29-year-old woman presented for management of acne vulgaris. Examination revealed a concerning hyperpigmented 7.1 x 17.5 mm band within the nail bed extending from the proximal nail fold to the hyponychium. Hyperpigmentation extended onto the proximal nail fold, even beyond the borders established by the band of melanonychia striata. Dermoscopy showed variability in width and color of the nail pigmentation (Figure 1). Also present was a dermal plaque with irregular borders and variegated brown to black pigmentation overlying the distal digit and extending from the pigmented region of the hyponychium (Figure 2).
Neither the nail nor digital pigmentation had undergone significant change throughout her life; there was no history of trauma, even at an early age. Personal and family histories were unremarkable for melanoma, Laugier-Hunziker syndrome, Peutz-Jeghers syndrome, or other mucocutaneous hyperpigmentation syndromes. Medications included a daily estrogen-progesterone oral contraceptive pill as well as tretinoin and hydroxychloroquine cream topically applied to acne areas.
Punch biopsy of the volar distal digit showed nests of banal-appearing melanocytes at the dermal-epidermal junction and within the dermis, admixed with pigment-laden macrophages. Dermal melanocytes infiltrated deep into the dermis and along adnexal structures in a pattern characteristic of congenital nevi (Figures 3A and 3B).
In rare instances, congenital nevi present subungually, with fewer than 20 biopsy-proven cases reported [1-12]. Interestingly, we found that nearly all of these congenital subungual melanocytic nevi feature periungual hyperpigmentation in association with longitudinal melanonychia, constituting a pseudo-Hutchinson sign, as was present in the current case. Additionally, at least four other reports describe congenital subungual melanocytic nevi with distal digital involvement [9, 10, 11, 12].
During fetal development, neural crest derived cell migration leads to the localization of active melanocytes within the dermis starting at 10 weeks gestational age. Whereas active melanocytes become more extensively distributed throughout the dermal tissues with the progression of gestation, dermal melanocytes are normally only found within a few anatomical areas, including the dorsal hands and feet, by the end of fetal development . This process is thought to occur both through redistribution to the epidermis as well as cell death. Around the time of the initial dermal localization at 10 weeks gestation, the nail apparatus also begins to form. Given the temporal relationship of these developmental processes and the nevus’s swirled pattern at the distal digit, the extensive nail unit and distal digital involvement in the current case may be explained by aberrant melanocyte migration within the forming nail matrix and acral skin.
Hutchinson sign, first described in 1886, is defined by longitudinal melanonychia extending into the periungual tissues . Whereas classically associated with an underlying melanoma, false positives or pseudo-Hutchinson sign are not infrequent ; studies evaluating the diagnostic test characteristics of Hutchinson sign are lacking in both the adult and pediatric populations. Aside from nail unit melanoma and congenital nevi, other entities to consider in the differential diagnosis include the following: ethnic pigmentation, trauma, systemic medical illness such as hyperthyroidism and Cushing syndrome, depositional disorders, medications, and syndromes of mucocutaneous hyperpigmentation . In our case, although only the distal digit was biopsied, the congenital onset, stable clinical history, morphology, and histopathology support the diagnosis of a congenital nevus involving both the distal digit and subungual areas. Nevertheless, in clinically worrisome melanocytic lesions, benign pathologic findings from punch or incisional biopsies cannot exclude sampling error. Therefore, either additional biopsies or complete excision may be warranted to exclude malignant transformation arising in a benign precursor. As previous authors have suggested, Hutchinson sign may not be an infallible sign of subungual melanoma  and requires further validation as a clinical tool. Whereas Hutchinson sign is one criterion for the ABC rule of subungual melanoma  and is traditionally considered a worrisome feature, it is certainly not pathognomonic and a malignant cause should not be assumed without thorough assessment.
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