Melanonychia 

Updated: Sep 10, 2018
Author: Chris G Adigun, MD, FAAD; Chief Editor: William D James, MD 

Overview

Background

Melanonychia is brown or black pigmentation of the nail unit. Melanonychia commonly presents as pigmented band arranged lengthwise along the nail unit, and this presentation is known as longitudinal melanonychia or melanonychia striata. The most concerning cause of melanonychia is subungual melanoma, although a variety of other causes includes physiologic longitudinal melanonychia, systemic disorders, trauma, inflammatory disorders, fungal infections, drugs, and benign melanocytic hyperplasias.[1, 2] See the image below.

Pigmented longitudinal streak secondary to a nail Pigmented longitudinal streak secondary to a nail matrix melanoma.

Pathophysiology

Melanonychia most often occurs because of increased production of melanin by melanocytes in the nail matrix. A healthy adult has approximately 200 melanocytes per mm2 in the nail matrix, of which the majority remain dormant. When these melanocytes are activated, melanosomes filled with melanin are transferred to differentiating matrix cells, which migrate distally as they become nail plate onychocytes.[3] This results in a visible band of pigmentation in the nail plate.

Etiology

When determining the etiology of longitudinal melanonychia, it is important to distinguish between melanocytic activation and melanocytic hyperplasia. Melanocytic activation is caused by an increased synthesis of melanin with a normal number of melanocytes. Melanocytic hyperplasia (including melanocytic nevi and melanoma) refers to an increased synthesis of melanin with an increased number of melanocytes. Nevi constitute 12% of longitudinal melanonychia cases in adults and 50% of longitudinal melanonychia cases in children. Note the clinical image below.

Longitudinal melanonychia secondary to a nevus. Longitudinal melanonychia secondary to a nevus.

Approximately two thirds of cases have a brown-black color, and one third of cases have periungual pigmentation (benign pseudo-Hutchinson sign). The bands are wider than 3 mm in greater than 50% of cases.

Below are the causes of melanonychia.[3, 6, 14, 15]

Melanocytic activation/hyperplasia–related causes are as follows:

  • Nevi

  • Melanotic macule of the nail unit

  • Melanocytic activation

  • Subungual melanoma

Physiologic causes of melanonychia are as follows:

  • Racial melanonychia (African American, Hispanic, Indian, Japanese, other dark-skinned races) (multiple bands)

  • Pregnancy (multiple bands)

Local and regional causes of melanonychia are as follows:

  • Trauma (acute or chronic) (single band)

  • Poor-fitting shoes (single band)

  • Onychotillomania (single band)

  • Nail biting (single band)

  • Carpal tunnel syndrome (single band)

  • Foreign body (subungual) (single band)

  • Radiation therapy (multiple bands)

  • Ultraviolet light (multiple bands)[16]

  • Postinflammatory hyperpigmentation (single band)

Systemic causes of melanonychia are as follows:

  • Addison disease (multiple bands)

  • Cushing syndrome (multiple bands)

  • Nelson syndrome (multiple bands)

  • Hyperthyroidism (multiple bands)

  • Hemosiderosis (multiple bands)

  • Hyperbilirubinemia (multiple bands)

  • Alcaptonuria (multiple bands)

  • Porphyria (multiple bands)

  • Acquired immunodeficiency syndrome (multiple bands)

  • Graft versus host disease (multiple bands)

  • Malnutrition (multiple bands)

  • Vitamin B-12 deficiency (multiple bands)

Dermatologic causes of melanonychia are as follows:

  • Psoriasis (multiple bands)

  • Lichen planus (multiple bands)

  • Chronic radiodermatitis (single bands)

  • Scleroderma (multiple bands)

  • Systemic lupus erythematosus (multiple bands)

  • Fungal infection of the nail bed (Aspergillus, Scopulariopsis, Candida, Blastomyces, Trichophyton,[17] Fonsecaea pedrosoi) (multiple bands)

  • Basal cell carcinoma (single band)

  • Bowen disease (single band)

  • Subungual fibrous histiocytoma (single band)

  • Mucous cyst (single band)

  • Lichen striatus (multiple bands)

Chemotherapeutic causes of melanonychia are as follows (multiple bands):

  • Bleomycin sulfate

  • Busulfan

  • Cyclophosphamide

  • Dacarbazine

  • Daunorubicin hydrochloride

  • Doxorubicin

  • Etoposide

  • 5-Fluorouracil

  • Hydroxyurea[18, 19]

  • Melphalan hydrochloride

  • Methotrexate

  • Nitrogen mustard

  • Nitrosourea

  • Tegafur

Other drug/agent-related causes of melanonychia are as follows (multiple bands):

  • Corticotropin

  • Amodiaquine

  • Amorolfine

  • Arsenic

  • Chloroquine

  • Clofazimine

  • Clomipramine

  • Cyclines

  • Diquat

  • Fluconazole

  • Fluoride

  • Gold salts

  • Ibuprofen

  • Ketoconazole

  • Lamivudine

  • Mepacrine

  • Mercury

  • Minocycline

  • Melanocyte-stimulating hormone

  • Polychlorinated biphenyl (PCB)

  • Phenytoin

  • Phenothiazine

  • Psoralen[16]

  • Roxithromycin

  • Steroids

  • Sulfonamide

  • Tetracycline

  • Thallium

  • Timolol

  • Zidovudine

Causes of melanonychia associated with a syndrome are as follows:

  • Laugier-Hunziker syndrome (multiple bands)[20]

  • Peutz-Jeghers syndrome (multiple bands)

  • Touraine syndrome (multiple bands)

Epidemiology

Frequency

Physiologic melanonychia is more common in darker-pigmented individuals. Seventy-seven percent of black individuals older than 20 years and almost 100% older than 50 years have evidence of this condition.[4, 5] Longitudinal melanonychia is present in 10-20% of Japanese individuals.[6] In the general white population, the prevalence of longitudinal melanonychia is 1.4%.[7]

In a study of 68 Hispanic patients with longitudinal melanonychia, melanonychia secondary to skin pigmentation was observed in 48 cases (68.6%).[8] Of the remaining patients, 6 (8.5%) were secondary to trauma, 5 (7.1%) were secondary to fungal infection, 4 (5.7%) were associated with benign melanocytic hyperplasia, and 4 (5.7%) had a nail apparatus malignancy. The remaining 3 (4.3%) cases were of mixed etiology.

The prevalence of affected individuals increases with age.[7, 9]

Race

The frequency of melanonychia varies by the degree of skin pigmentation, as described in Frequency, International.

Sex

Melanonychia affects males and females equally.[9]

Age

Typically, melanonychia is more common in older individuals. In children, melanonychia is often caused by melanocytic nevi. Subungual melanoma or melanoma in situ is very rare in children,[10, 11] but has been reported.[12]

Prognosis

In cases of melanonychia associated with systemic diseases, treatment of the primary condition may improve the nail pigmentation. Similarly, discontinuation of any offending drugs may improve melanonychia.

The prognosis of patients with subungual melanoma is poor. In a 2007 series of 106 subungual melanomas, 48 (45%) patients developed a recurrence or metastasis and, of these, 33 (69%) died from their disease during the follow-up period (median 56 mo). Patients with a melanoma deeper than 2.5 mm had a statistically worse survival rate than those with thin melanomas. Melanonychia secondary to subungual melanoma has the highest morbidity and mortality compared with other body sites, with reported 5- and 10-year survival rates of 30% and 13%, respectively.[13]

Patient Education

Patients should be instructed to follow lesions of suspected benign causes of longitudinal melanonychia for any change in color, pattern, size of the band, or new onset pain and/or ulceration, as these can be signs of subungual melanoma.

 

Presentation

History

Most melanonychia patients present with a history of asymptomatic hyperpigmentation of the nail plate.

A careful history should include information on medications, past treatments, hobbies, illnesses, family history, any history of trauma to the area, prior history of a biopsy of the nail unit, number of nails affected, results of any prior nail clippings sent for histologic examination, results of cultures sent for infectious organisms, change of appearance of the band (or bands) over time, and ethnic background.[21]

In cases of subungual melanoma, the patient may describe a long-standing history of longitudinal melanonychia that recently changed in appearance. Changes that warrant concern include alteration of color, pattern, or size of the band; new onset of pain or ulceration in the site of longitudinal melanonychia;[22] or the presence of subungual blood.[23]

Physical Examination

Melanonychia is characterized by a tan, brown, or black discoloration of the nail unit and is often observed in the nail plate. The nail plate may be diffusely involved, or only a single longitudinal band may be present. Transverse melanonychia has also been rarely reported. One or more digits may be involved.

Levit et al identified characteristics of melanonychia that should warrant concern for subungual melanoma, and they used the acronym ABCDEF to describe them, as follows[24] :

  • (A) Age: The peak incidence in the fifth to seventh decade of life. Additionally, subungual melanoma accounts for one third of melanoma cases in Asians, African Americans, and Native Americans.

  • (B) Brown-black band with breadth greater than 3 mm with variegated borders

  • (C) Change in nail band morphology despite treatment

  • (D) Digit involved: The thumb is more likely to be affected by subungual melanoma than the great toe; the great toe is more likely than the index finger to be affected by subungual melanoma.

  • (E) Extension of the brown-black pigment of the nail bed, nail matrix, and/or nail plate onto the adjacent cuticle and proximal and/or lateral nail folds (Hutchinson sign)

  • (F) Family or personal history of dysplastic nevus or melanoma

Careful examination of the oral and genital mucosa may provide important diagnostic clues to identify Peutz-Jeghers syndrome or Laugier-Hunziker syndrome.[20, 25]

 

DDx

Differential Diagnoses

  • Melanotic macule of the nail unit

  • Nail matrix nevus

  • Onychomycosis

  • Subungual hematoma

  • Subungual melanoma

 

Workup

Laboratory Studies

If an infectious etiology is suspected, a nail plate clipping should be sent for histologic analysis and appropriate cultures.[3]

Depending on the suspected systemic and/or dermatologic causes, appropriate laboratory tests should be ordered.

Other Tests

Examination of affected nails with a dermatoscope can provide useful information regarding both the etiology and location of longitudinal melanonychia.[26] Considering the dermatoscopic appearance of subungual nevi and subungual melanoma, nevi have been reported to demonstrate regular parallel lines, while subungual melanoma has been reported to demonstrate irregular lines with some disruption of parallelism.

In an effort to differentiate neoplastic from reactive processes of the nail apparatus, additional dermoscopic features have been described by Ronger et al and Braun et al.[25, 26, 27] These features include blood spots, brown coloration of the background, grayish background and thin gray lines, micro-Hutchinson sign, and microscopic grooves. Of these dermoscopic patterns, the features that most commonly occur with melanoma include a brown background hue, the presence of irregular longitudinal lines, and the presence a micro-Hutchinson sign. The micro-Hutchinson sign has been described as pigmentation of the cuticle that is only appreciable with use of a dermatoscope.[26] The diagnostic algorithms described by Ronger et al and Braun et al describe 2 forms of pigment: grayish color and brownish color. Grayish color suggests focal melanocyte activation in the absence of melanocytic hyperplasia. Brownish color suggests melanocytic hyperplasia.

These dermoscopic criteria may be applied in the decision about whether to perform a biopsy and the location of the biopsy. Adigun et al suggest biopsy should be performed when longitudinal melanonychia reveals irregular lines or the micro-Hutchinson sign.[28] If dermoscopic evaluation reveals a reassuring regular pattern of parallel lines, the decision to observe every 6 months may be sufficient.

Procedures

Longitudinal melanonychia of a single nail unit in an adult is concerning, and a biopsy of the nail unit can evaluate for the possibility of melanoma, which cannot be differentiated from benign causes of longitudinal melanonychia solely based on clinical examination.[29]

Dermatoscopic examination of the free edge of the nail plate can help to determine the origin of longitudinal melanonychia within the nail unit and can therefore be helpful in determining which anatomic area of the nail unit requires biopsy. If the pigmentation is in the lower portion (ventral aspect) of the nail plate, the origin of pigmentation is in the distal nail matrix. Conversely, if the pigmentation is in the upper portion (dorsal aspect) of the nail plate, the origin of pigmentation is in the proximal nail matrix.[30, 31] Pigmentation present throughout the nail plate indicates a lesion that extends from the proximal to distal nail matrix. An adjunct to this technique is to perform a nail clipping of the affected distal nail plate and to stain this specimen with a Fontana-Masson histologic stain. The portion of the nail plate affected by melanonychia is then easily visualized.

A variety of surgical techniques can be used to sample pigmented lesions located within the nail matrix, including the punch biopsy, matrix shave biopsy, and lateral longitudinal excision.[32, 33, 34]

For bands less than or equal to 3 mm, a 3-mm punch biopsy can be used if the origin of the band is located in the distal matrix. The risk of causing a subsequent nail plate dystrophy after the procedure is greater the further proximal the area of the matrix that is sampled.

After reflection of the proximal nailfold, to expose the nail matrix, a 3-mm punch is performed, sampling the origin of the pigmented band. The punch is pressed through the nail matrix and down to the underlying bone. Once the biopsy specimen is removed, it can be inked to help the pathology staff best orient the specimen before processing. Depending on the nature of the surgical techniques used, some control of hemostasis may be required. The proximal nailfold is returned to its initial location, and it can be secured in place by a variety of methods.

The matrix shave is useful for pigmented bands that originate in the proximal matrix, bands that are in the central portion of the nail unit, and/or those that measure 3-6 mm in diameter. This technique was originally described by Eckart Haneke and has the advantage of causing less nail dystrophy post procedure because a full-thickness wound is not created in the nail matrix.

To perform the nail matrix shave, the proximal nail fold is reflected to expose the matrix, and then the proximal nail plate is also reflected away from the biopsy site. The origin of the pigmented band in the nail matrix is scored with 1- to 2-mm margins with a scalpel blade, which is followed by removal of the area using a shave technique by gently passing the blade under the pigmented area, removing only a small thickness of epithelium. Titanium-coated scalpel blades have been reported to be particularly effective to obtain optimal results with this technique. The proximal nail plate and nail fold are then returned to their original anatomic positions.[32] The specimen can be inked for orientation, and it may be placed on a piece of filter paper before being put in a formalin-filled container to prevent curling.

A lateral longitudinal excision is useful for pigment that is in the lateral 30% of the nail unit.[35] In this procedure, a near elliptical excision is made. The scalpel is inserted 1-2 mm medial to the pigmented band halfway between the cuticle and distal interphalangeal crease and extended distally 3-4 mm onto the digital bed. The scalpel is again inserted proximally at the starting point and moved laterally around the matrix horn, curving medially at the hyponychium to meet the endpoint of the first incision. The tissue is removed with fine-tipped scissors with the “tips down” in a distal-proximal fashion.[32]

In order to visualize anatomic structures within the nail unit, the nail plate is commonly removed during nail surgery. Complete nail plate avulsion is less favorable than partial nail avulsion because of a higher comparative likelihood of complications, including postoperative pain, distal plate embedding, and dorsal pterygium formation. Alternatives to complete nail plate avulsion include partial nail plate avulsion techniques, such as the trap door avulsion, longitudinal partial plate avulsion, window nail plate avulsion, partial distal nail plate avulsion, and lateral nail plate avulsion.[31, 36]

When clinical suspicion is high for subungual melanoma, it is important to sample the entire pigmented lesion with a full-thickness excision, because a partial biopsy may lead to a delay in diagnosis.[37]

When possible, the source of the pigment production should be removed via biopsy to prevent recurrence of longitudinal melanonychia.

Excisions larger than 3 mm and those from the proximal matrix are more likely to produce permanent nail dystrophy.[32]

Histologic Findings

The histopathologic findings vary based on the etiology of melanonychia.

Nail matrix nevi can have an unusual appearance histologically, and they are considered to be “special site nevi,” a subset of acral pigmented lesions. The majority of nail matrix nevi are junctional, although compound nail matrix nevi have been reported. Histologically, nail matrix nevi can be highly cellular; can have hyperchromatic, large cells that do not form discrete nests; and can possess prominent, abundant, and uneven cytoplasmic dendrites.[38]

One study evaluated 20 subungual melanomas and 15 benign subungual melanotic macules to determine the histopathologic features that can help to differentiate these 2 entities. A statistically significant difference in the mean melanocyte count (number of melanocytes per 1-mm stretch of subungual dermoepithelial junction) was noted for invasive melanoma (mean 102; range 51-212) compared with subungual melanotic lentigines (mean, 15.3; range 5-31). Other histopathologic features seen in subungual melanoma compared with subungual melanotic macules included a confluence of melanocytes, multinucleation of melanocytes, florid pagetoid spread of melanocytes, inflammation at the epithelial stromal interface, and moderate and/or severe cytologic atypia of melanocytes.[39]

A Fontana-Masson stain highlights melanin and thus may be useful in the determination of location of pigment within the nail matrix epithelium. Of note, 20-30% of subungual melanomas may be amelanotic,[24, 40] and immunostains for melanocytes, such as S-100, Melan-A, HMB-45, and MITF, may provide important diagnostic information.

 

Treatment

Medical Care

If melanonychia is secondary to systemic and/or dermatologic disease, treatment of the underlying condition is helpful.

If melanonychia is secondary to a drug, discontinuation of the offending agent may result in clearance.

Surgical Care

For melanoma in situ, total excision of the nail apparatus or Mohs micrographic surgery is indicated.[41]

For invasive melanoma, amputation of the distal phalanx may be indicated.[42] Albeit controversial, total nail bed excision and reconstruction using a full-thickness graft may be considered. In a large case series, the 5-year survival rates for cutaneous melanoma of the hand versus subungual melanoma treated with a wide local excision was reported as 100% and 80%, respectively.[43] . This was due to a delay in diagnosing subungual lesions, which averaged 3.68 mm in depth versus 1.36 mm for hand melanomas of the cutaneous surface.

Because diagnosis is often delayed in these patients, sentinel lymph node biopsy after surgery may be warranted.[44]

Consultations

Because longitudinal melanonychia is associated with a variety of systemic conditions, these cases may require referral to the appropriate specialist in order to manage the primary disease.

In cases of subungual melanoma with a poor prognosis, consultation with a hematologist/oncologist regarding potential chemotherapeutic options may be warranted.

Complications

Postoperative nail dystrophy is a common complication and should be taken into consideration before a nail biopsy is performed.[6] Postoperative nail dystrophy is less likely to occur with biopsies of the distal matrix than biopsies of the proximal matrix.

Complete excision when longitudinal melanonychia is located in the lateral third of the nail unit with a lateral longitudinal excision is a sampling method that may result in less cosmetic deformity than other methods.

Long-Term Monitoring

Patients with longitudinal melanonychia of a single digit who decline a biopsy should receive close follow-up with their dermatologist, and monitoring of the melanonychia should be part of a routine monthly self-skin examination. Additionally, the physician may use a dermatoscope to monitor melanonychia.

If changes suggestive of melanoma are observed, a biopsy should be performed.

 

Medication

Medication Summary

Definitive medical therapy should be considered when melanonychia results from another systemic, dermatologic, or infectious disease process.

 

Questions & Answers

Overview

What is melanonychia?

What is the pathophysiology of melanonychia?

What are the melanocytic activation/hyperplasia–related causes of melanonychia?

What causes melanonychia?

What are the physiologic causes of melanonychia?

What are the local and regional causes of melanonychia?

What are the systemic causes of melanonychia?

What are the dermatologic causes of melanonychia?

What are the chemotherapy-related causes of melanonychia?

Which drugs cause melanonychia?

Which syndromes are associated with melanonychia?

What is the prevalence of melanonychia?

What is the racial predilection of melanonychia?

What is the sexual predilection of melanonychia?

Which age groups have the highest prevalence of melanonychia?

What is the prognosis of melanonychia?

What is included in patient education about melanonychia?

Presentation

Which clinical history findings are characteristic of melanonychia?

Which physical findings are characteristic of melanonychia?

Which history and physical findings are characteristic of subungual melanoma in melanonychia?

DDX

What are the differential diagnoses for Melanonychia?

Workup

What is the role of lab testing in the workup of melanonychia?

What is the role of dermatoscopy in the workup of melanonychia?

What is the role of biopsy in the workup of melanonychia?

Which histologic findings are characteristic of melanonychia?

Treatment

How is the underlying etiology of melanonychia treated?

What is the role of surgery in the treatment of melanonychia?

Which specialist consultations are beneficial to patients with melanonychia?

What are the possible complications of melanonychia treatment?

What is included in the long-term monitoring of patients with melanonychia?

Medications

When are medications used in the treatment of melanonychia?