A 62-year-old African American man presents to establish care and to undergo skin examination, which he reports receiving regularly since his sister was diagnosed with melanoma. Examination reveals 3-mm hyperpigmented horizontal bands across the nailbeds of all fingernails, which he reports have been present since his 20s. He denies experiencing any other nail changes or pain. He takes no medications, and he has no history of skin cancer or suspicious moles. He has no relevant medical history.
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Melanonychia is a common dermatologic condition involving black or brown pigmentation of the nail. While typically a benign finding, it has a wide differential and requires a detailed history and examination to rule out serious and potentially life-threatening conditions such as subungual melanoma.
Classifications of melanonychia include longitudinal and, rarely, transverse melanonychia. Longitudinal melanonychia typically originates from the distal nail matrix, where melanocytes are more active. It can be further classified into exogenous pigmentation, such as blood from trauma, and endogenous pigmentation, such as melanin. The origin of pigmentation can help determine the underlying pathology; for example, there are 2 common mechanisms that result in melanin production. Melanocytic activation occurs without a change in cell number, while melanocytic hyperplasia involves an increase in the number of melanocytes.1
Melanonychia may be physiologic or pathologic. Physiologic melanonychia includes melanonychia associated with pregnancy and ethnic melanonychia in individuals with darker skin tones. Prevalence, number of bands, and band width also increase with age. One study noted that 77% of the African American population had melanonychia by 20 years of age, and melanonychia was present in nearly 100% of those aged ≥50 years.1 In comparison, the prevalence of melanonychia in the white population is 1.4%.2 Prevalence does not appear to differ based on gender.3
Pathologic causes of melanonychia can be broadly categorized as localized or systemic. Localized causes include trauma, such as poor-fitting shoes or nail biting; infectious causes, such as onychomycosis; dermatologic conditions, such as lentigines, nevi, and subungual melanoma; and postinflammatory changes. Systemic causes include chemotherapy, medications, endocrine disorders, and a variety of syndromes including AIDS, Laugier-Hunziker syndrome, Peutz-Jeghers syndrome, hemochromatosis, and porphyria.4,5
The 2 most common causes of melanonychia in adults are lentigines followed by nevi. This differs from pediatric melanonychia, for which nevi account for approximately 50% of cases.6
When a patient presents with melanonychia, it is crucial to rule out skin cancers, especially subungual melanoma. This is especially important given the fact that two-thirds of cases of subungual melanoma first present with longitudinal melanonychia. Because presentation of the two conditions can be so similar, subungual melanoma is commonly misdiagnosed with an average delay in diagnosis of 2 years.5 This delay has a significant impact on the patient’s morbidity and mortality given that subungual melanoma has a significantly worse prognosis than its cutaneous counterpart.7
Due to the wide differential, a thorough history and physical examination are vital for the proper diagnosis and management of melanonychia. Pertinent information includes the time of onset, any corresponding trauma, changes in appearance or size, number and location of nails affected, presence of pain or ulceration, recent medications, and medical and family history. Physical examination findings should involve assessment of all 20 nails, with notation of the location of the lesion, presence or absence of extension into surrounding structures, number of bands, size, pigmentation pattern, and borders.4 Levit et al published a helpful mnemonic for identifying subungual melanoma8:
A = age of patient (peaks in the fifth to seventh decade of life) and race (up to one-third of all subungual melanoma cases are in African Americans, Asians, and native Americans)
B = brown-to-black with a breadth of >3 mm and borders that are variegated
C = change in nail band or lack of change in nail morphology despite adequate treatment
D = the digit most commonly involved (thumb > hallux > index finger, dominant hand, only one digit involved)
E = extension of the pigment onto the proximal and/or lateral nail fold (ie, Hutchinson sign)
F = family or personal history of dysplastic nevus or melanoma
The physical examination can help to distinguish whether the pigmentation is endogenous or exogenous as many exogenous pigments, such as potassium permanganate, can simply be scraped off of the nail surface. In cases of melanonychia, dermoscopy has been shown to be more effective than clinical observation in the evaluation of the lesions. A grey background with regular parallel lines typically represents melanocytic activation including ethnic melanonychia, lentigines, and drug-induced pigmentation. Dermoscopic findings that are concerning for melanoma include wide bands and the Hutchinson sign, as well as irregular pigmentation, thickness, and borders. Subungual hematomas often present as red or purple pigmented globules with peripheral fading; however, the presence of blood does not rule out malignancy. Examination of the mucosa aids in the identification of Laugier-Hunziker and Peutz-Jeghers syndromes, which are also associated with melanonychia.4
Once melanonychia has been identified, further workup is largely dependent on the differential diagnosis developed based on the history, physical examination, and all other collateral information. This workup may include nail-clipping cultures for evaluation of infectious etiologies, regular follow-up for observation of benign-appearing pigmentation pattern, or histopathologic examination for suspicious pigmentation patterns or history.9 Despite the various approaches that can be taken, histopathology remains the gold standard for the diagnosis of melanonychia. The histopathologic findings characteristic of subungual melanocytic nevi include well-formed nests of melanocytes at the junction of the nail matrix and dermis. Lentigines and melanomas may be difficult to distinguish histopathologically, but melanoma is more likely to have a high concentration of melanocytes at the dermo-epithelial junction and cytologic atypia, multinucleation, or florid pagetoid spread of melanocytes.10 Treatment also varies based on the underlying etiology but may include antifungal agents or antibiotics for infectious causes, discontinuation of the offending drug, or surgical excision.4 Cases of melanonychia should be referred for evaluation by a board-certified dermatologist to ensure that melanoma is ruled out.
In this case, the clinical presentation was consistent with a benign form of melanonychia. The presence of nearly identical transverse melanonychia across all 10 fingernails was a reassuring sign that the hyperpigmentation was benign in origin. If the pigmentation were more irregular and only present on 1 nail, biopsy would have been strongly considered. The hyperpigmented bands were measured and the patient was followed in clinic for routine skin assessments.
Katherine Park is a medical student, Joan Fernandez is a medical student, and Christopher Rizk, MD, is a dermatology resident at the Baylor College of Medicine in Houston.
- Andre J, Lateur N. Pigmented nail disorders. Dermatol Clin. 2006;24(3):329-339.
- Duhard E, Calvet C, Mariotte N, Tichet J, Vaillant L. [Prevalence of longitudinal melanonychia in the white population]. Ann Dermatol Venereol. 1995;122(9):586-590.
- Leung AK, Robson WL, Liu EK, et al. Melanonychia striata in Chinese children and adults. Int J Dermatol. 2007;46(9):920-922.
- Braun RP, Baran R, Le Gal FA, et al. Diagnosis and management of nail pigmentations. J Am Acad Dermatol. 2007;56(5):835-847.
- Jefferson J, Rich P. Melanonychia. Dermatol Res Pract. 2012;2012:952186.
- Goettmann-Bonvallot S, Belaich AJ. Longitudinal melanonychia in children: a clinical and histopathologic study of 40 cases. J Am Acad Dermatol. 1999;41(1):17-22.
- Banfield CC, Redburn JC, Dawber RPR. The incidence and prognosis of nail apparatus melanoma. A retrospective study of 105 patients in four English regions. Br J Dermatol. 1998;139:276-279.
- Levit EK, Kagen MH, Scher RK, Grossman M, Altman E. The ABC rule for clinical detection of subungual melanoma. J Am Acad Dermatol. 2000;42:269-274.
- Piraccini BM, Dika E, Fanti PA. Tips for diagnosis and treatment of nail pigmentation of nail pigmentation with practical algorithm. Dermatol Clin. 2015;33:185-195.
- Amin B, Nehal KS, Jungbluth AA, et al. Histological distinction between subungual lentigo and melanoma. Am J Surg Pathol. 2008;32:835-843.