A four-year-old boy presents with a newly pigmented line on his right thumb for 6 months. He already had one pigmented line on that same thumb since age one. His parents want to know if this pigmentation is dangerous. The child is otherwise healthy. On examination there are two longitudinal pigmented lines easily visible on the right thumbnail (Figure 161-1A). The boy is referred to a pediatric dermatologist. Examination with a dermatoscope shows the details of the many lines and confirms his concern for melanoma (Figure 161-1B). The concerns are expressed to the parents and the child is set up for a nail matrix biopsy with sedation. The differential diagnosis also includes a congenital melanocytic nevus that is growing.
A. Longitudinal melanonychia on the right thumb of four-year-old boy with two prominent pigmented lines. One of the two lines is new. B. Dermoscopic examination of the nail shows the complex pigment pattern with many lines and melanocytic dots. This is suspicious for melanoma but could also be a congenital nevus that is growing. (Used with permission from Richard P. Usatine, MD.)
Atypical pigmentation of the nail plate may result from many nonmalignant causes, such as fungal infections, benign melanocytic hyperplasia, nevi and medications. It may also result from development of subungual melanoma. The challenge for the clinician is separating the malignant from the nonmalignant sources.
Longitudinal melanonychia (LM) is a clinically descriptive term that represents a longitudinal pigmented band in the nail plate (Figures 161-1 to 161-3). It may be caused by any of the conditions listed above but is often due to normal ethnic hyperpigmentation (Figure 161-3). It may involve 1 or several digits, vary in color from light brown to black, vary in width (most range from 2 to 4 mm), and have sharp or blurred borders.
Longitudinal melanonychia—a single dark band of nail pigment appearing in the matrix region and extended to the tip of the nail. This is concerning for melanoma. The widening of the band in the proximal nail shows that the melanocytic lesion in the matrix is growing. A biopsy showed this to be a benign nevus. (Used with permission from Richard P. Usatine, MD.)
During a routine sports physical for a black adolescent boy, a translucent darker stipe was discovered in the nail plate of one of his thumbs. The line was faint and uniform in width. He was reassured it was most likely benign but the lesion was noted in his medical record so it could be rechecked in the future and he was instructed to return to clinic if it rapidly changed. (Used with permission from E.J. Mayeaux, Jr., MD.)
Acrolentiginous melanoma = acral lentiginous melanoma, subungual melanoma is one type of acral lentiginous melanoma involving the nail unit.
LM is more common in more darkly pigmented persons. It occurs in 77 percent of African Americans older than age 20 years and in almost 100 percent of those older than age 50 years.1,2 It also occurs in 10 to 20 percent of persons of Japanese descent. LM is common in Hispanic and other dark-skinned groups. LM is unusual in whites, occurring in only approximately 1 percent of the population.1
Melanoma is the seventh most common cause of cancer in patients in the US. Subungual melanoma is a relatively rare tumor with reported incidences between 0.7 percent and 3.5 percent of all melanoma cases in the general population.3
Etiology and Pathophysiology
LM originates in the nail matrix and results from increased deposition of melanin within the nail plate. This deposition may result from greater melanin synthesis or from an increase in the total number of melanocytes (Figure 161-4). Pigment clinically localized within the dorsal half of the nail plate indicates a proximal matrix origin, and pigment localized within the ventral nail plate indicates a distal matrix origin. Look at the distal edge of the nail in a cross-sectional view to see whether the pigment is dorsal or ventral (a dermatoscope may help).
LM may also be caused by chronic trauma, especially in the great toes.
Inflammatory changes accompanying skin diseases located in the nail unit, such as psoriasis, lichen planus, amyloidosis, and localized scleroderma, rarely may result in LM.
Benign melanocytic hyperplasia (lentigo) is observed in 30 percent of the pediatric cases of single-biopsied LM.4
Nevi represent almost 50 percent of cases in children. A brown-black coloration is observed in two thirds of the cases and periungual pigmentation (benign pseudo-Hutchinson sign) in 1/3.
Certain drugs may also cause LM, especially chemotherapeutic agents, and antimalarial drugs (mepacrine, amodiaquine, and chloroquine).
Endocrine disorders, such as Addison disease, Cushing syndrome, hyperthyroidism, and acromegaly, can be responsible for LM.
The diagnosis of subungual melanoma must always be considered in patients with LM (Figures 161-5 to 161-7). Separating benign from malignant lesions is often difficult. Both arise most often in the thumb or index fingers, and both are more common in dark-skinned persons.5 A biopsy should be performed if the cause of LM is suspicious for melanoma. Table 161-1 lists diagnostic clues for subungual melanomas. Many subungual melanomas have a history of trauma preceding the diagnosis so it is important to not be fooled by this history (Figure 161-7).
Hutchinson sign is the extension of pigmentation to the skin adjacent to the nail plate involving the nail folds or the fingertip. It is an important indicator for nail melanoma (Figures 161-5 to 161-6).6
Pseudo-Hutchinson sign is the presence of dark pigment around the proximal nail fold secondary to benign conditions such as racial melanosis and not melanoma (Figure 161-8). Another cause of pseudo-Hutchinson sign is a translucent cuticle below which the pigment of LM is visible. Trauma and drug-induced pigmentation can also produce a pseudo-Hutchinson sign.
Subungual melanoma arises on the hand in 45 to 60 percent of cases, and most of those occur in the thumb (Figures 161-5 to 161-6).4 On the foot, subungual melanoma usually occurs in the great toe.5 The median age at which subungual melanoma is usually diagnosed is in the sixth and seventh decades. It appears with equal frequency in males and females.5
TABLE 161-1Diagnostic Clues that Indicate Longitudinal Melanonychia is Suspicious for Subungual Melanoma ||Download (.pdf) TABLE 161-1 Diagnostic Clues that Indicate Longitudinal Melanonychia is Suspicious for Subungual Melanoma
|Hutchinson sign (melanoma until proven otherwise) |
|In a single digit |
|Sixth decade of life or later |
|Develops abruptly in a previously normal nail plate |
|Suddenly darkens or widens (change in the LM morphology) |
|Occurs in either the thumb, index finger, or great toe |
|History of digital trauma |
|Dark-skinned patient, particularly if the thumb or great toe is affected |
|Blurred, rather than sharp, lateral borders |
|Personal history of malignant melanoma |
|Increased risk for melanoma (e.g., familial atypical mole and melanoma [FAMM] syndrome) |
|Nail dystrophy, such as partial nail destruction or disappearance |
Longitudinal melanonychia of the toenail of a young person. Biopsy demonstrated benign melanocytosis. (Used with permission from Richard P. Usatine, MD.)
Acral lentiginous melanoma of the thumb with a very positive Hutchinson sign. Note how the pigmented band on the nail is greater than 3 mm in width. (Used with permission from Robert T. Gilson, MD.)
Advanced acral lentiginous melanoma of the thumb with destruction of the nail plate and ulceration. Note the hyperpigmentation of the proximal nail fold (Hutchinson sign), which is strongly indicative of melanoma. (Used with permission from Dr. Dubin at http://www.skinatlas.com.)
Nodular melanoma growing within the pinkie nail (not the thumb) of a young woman. The patient claims that it started with a dark spot under the nail of this fifth digit after she caught it in a dresser drawer. When it did not heal she pursued medical care and was treated for a presumed nail fungus and then a paronychia until she was finally seen by a physician who recognized the gravity of this situation. A biopsy was performed immediately and it showed a thick nodular melanoma greater than 3 mm in depth with a high mitotic index and ulceration. The patient will undergo an amputation of the finger at the PIP joint along with a sentinel node biopsy. (Used with permission from Richard P. Usatine, MD.)
The fingers of this child demonstrate longitudinal melanonychia with pseudo-Hutchinson sign that was found to be due to racial melanosis. The small bruise on the proximal nail fold of the right thumb was due to recent trauma and not melanoma. (Used with permission from Richard P. Usatine, MD.)
Table 161-1 lists diagnostic clues that indicate an increased risk for the presence of subungual melanoma.
There is an ABCDEF mnemonic system that applies to subungual melanoma:
In this system “A” stands for age (peak incidence being between the fifth to seventh decades) and African Americans, Asians, and Native Americans in whom subungual melanoma accounts for 1/3 of melanoma cases.
“B” stands for “brown to black” and with “breadth” of 3 mm or more.
“C” stands for change in the nail band coloration or lack of change after adequate treatment.
“D” stands for the digit most commonly involved.
“E” stands for extension of the pigment onto the proximal and/or lateral nailfold (Hutchinson sign).
“F” stands for family or personal history of dysplastic nevus or melanoma.
The digits used for grasping (thumb, index finger, and middle finger) are the most commonly involved in LM and melanoma, but either may be found in any finger or toe.
Definitive diagnosis of a nail discoloration may be made with a biopsy of the nail matrix. Patients with darker skin color and multiple digits with translucent LM often need only be observed. Single dark lines in whites should always be biopsied. A 3-mm punch biopsy can be performed at the origin of the darkest part of a dark band within the nail matrix (Figure 161-9). Histologic diagnosis of atypical melanocytic hyperplasia necessitates the complete removal of the lesion.
A. The proximal nail fold is reflected back to perform a nail matrix biopsy in a young man with new onset of longitudinal melanonychia. The 3-mm punch is placed over the origin of the dark band at the distal matrix. B. The 3-mm punch now contains the specimen for pathology. The longitudinal melanonychia was caused by melanocytic hyperplasia. (Used with permission from Richard P. Usatine, MD.)
Pigmented lesions in the nail bed usually do not cause LM and are viewed through the nail as a grayish to brown or black spot.7
Subungual hematoma may be confused with LM, but the color grows out with the nail plate, exhibiting a proximal border that reproduces the shape of the lunula. A hole punched in the nail plate allows for the visualization of the underlying nail bed and confirmation of the nature of the coloration (see Chapter 166, Subungual Hematoma).
No treatment is required for benign LM.
Referral Or Hospitalization
Treatment of primary subungual melanomas includes amputation at the level of the interphalangeal joint for thumb lesions, SOR B the distal or proximal interphalangeal joint for fingers, SOR C and the metatarsophalangeal joint for toes.8 For melanoma in situ, it may be possible to remove the full nail apparatus and save the digit. Sentinel lymph node biopsy is often indicated to establish the disease stage. Chemotherapy is recommended for nodal or visceral metastases.
The 5-year survival is approximately 74 percent for patients with stage I subungual melanoma and 40 percent for patients with stage II disease. Prognostic variables negatively affecting survival include stage at diagnosis, deeper Clark level of invasion, African American race, and ulceration.9
Because LM may indicate an undiagnosed melanoma of the nail unit, biopsy, or regular monitoring is extremely important. If there is any doubt about the diagnosis of melanoma, biopsy immediately or refer to someone who can. Have the patient report any changes in pigmentation of the nail plate or nail folds, and strongly consider biopsy in these individuals.
DermNet NZ. Nail Diseases—http://dermnetnz.org/hair-nails-sweat/nails.html.
eMedicine. Nail Surgery—www.emedicine.com/derm/topic818.htm.
Braun RP, Baran R, Le Gal FA, et al. Diagnosis and management of nail pigmentation. J Am Acad Dermatol. 2007;56:5 835-847.
Jellinek N. Nail matrix biopsy of longitudinal melanonychia: diagnostic algorithm including the matrix shave biopsy. J Am Acad Dermatol. 2007;56:5 803-810.
Usatine R. Nail procedures. In: Usatine R, Pfenninger J, Stulberg D, Small R, eds. Dermatologic and Cosmetic Procedures in Office Practice. Philadelphia, PA: Elsevier; 2012:216-228. The whole procedure depicted in Figure 161-9 is described in detail.
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CP: Subungual melanoma: an eighteen year review. Surgery. 1994;116:96–100.
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C: Linear melanonychia due to subungual keratosis of the nail bed: report of two cases. Br J Dermatol. 1999;140:730–733.
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