A 53-year-old Hispanic woman requests treatment for idiopathic guttate hypomelanosis, or white spots, on her legs. During the physical examination, a dark streak is observed traversing the patient’s right thumb nail (Figure). The patient works as a laborer but denies any trauma to the site. She does not recall when this condition first appeared or whether significant darkening has occurred over the past few months. The patient is not taking oral medication, and she does not have a history of systemic disease. Her remaining fingernails and toe nails are devoid of pigmented bands.
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Longitudinal melanonychia, also known as melanonychia striata, is characterized by a brown or black discoloration traversing the nail lengthwise. The prevalence of longitudinal melanonychia varies by race; the condition is most common in black individuals followed by Hispanic and Asian individuals.1,2 The condition results from deposits of melanin in the nail plate that is produced by melanocytes located in the suprabasal layer of the nail matrix.1,3
Differential diagnosis of longitudinal melanonychia includes hemorrhage secondary to trauma and pigmentation induced by drugs or other malignancies.4,5 Although the majority of longitudinal melanonychia cases are benign, subungual melanomas represent a significant subset.6 Dermoscopic examination of subungual melanoma may reveal irregular pigmentation and early Hutchinson sign (pigmentation extending into the nail folds); however, definitive diagnosis requires histopathologic examination.7,8 Melanoma of the nail, although most common in adults aged 50 to 70 years, can also occur in children.9
Stephen Schleicher, MD, is director of the DermDox Center for Dermatology, associate professor of medicine at Commonwealth Medical College, and clinical instructor of dermatology at Arcadia University and Kings College.
- Baran R, Kechijian P. Longitudinal melanonychia (melanonychia striata): diagnosis and management. J Am Acad Dermatol. 1989;21(6):1165-1175.
- Dominguez-Cherit J, Roldan-Marin R, Pichardo-Velazquez P, et al. Melanonychia, melanocytic hyperplasia, and nail melanoma in a Hispanic population. J Am Acad Dermatol. 2008;59(5):785-791.
- Theunis A, Richert B, Sass U, Lateur N, Sales F, André J. Immunohistochemical study of 40 cases of longitudinal melanonychia. Am J Dermatopathol. 2011;33(1):27-34.
- Nguyen AL, Körver JE, Theunissen CC. Longitudinal melanonychia on multiple nails induced by hydroxyurea. BMJ Case Rep. 2017;2017.
- Gatica-Torres M, Arguello-Guerra L, Manuel Ruiz-Matta J, Dominguez-Cherit J. Subungual pigmented squamous cell carcinoma presenting as a grey longitudinal melanonychia in a young patient. BMJ Case Rep. 2016;2016.
- Jin H, Kim JM, Kim GW, et al. Diagnostic criteria for and clinical review of melanonychia in Korean patients. J Am Acad Dermatol. 2016;74(6):1121-1127.
- Ronger S, Touzet S, Ligeron C, et al. Dermoscopic examination of nail pigmentation. Arch Dermatol. 2002;138(10):1327-1333.
- Koga H, Saida T, Uhara H. Key point in dermoscopic differentiation between nail apparatus melanoma and benign longitudinal melanonychia. J Dermatol. 2011;38:25-34.
- Iorizzo M, Tosti A, Di Chiacchio N, et al. Nail melanoma in children: differential diagnosis and management. Dermatol Surg. 2008;34:974-978.