Given the common nature of longitudinal melanonychia, the potential link to melanoma in some cases and the varied differential diagnosis, this author offers salient diagnostic insights, assesses the utility of dermoscopy and emphasizes appropriate nail unit biopsy technique.
Longitudinal melanonychia, the presence of pigmented streaks in nail plates, is a common and often perplexing problem for clinicians. Why is it perplexing? Although most presentations of melanin deposition in nail plate tissue represent a benign melanocytic process in the nail matrix, a small percentage may represent melanoma, a potentially fatal cancer. For this reason, accurate diagnosis at the earliest possible moment can be critical in revealing a nail unit melanoma at a stage that is curable.
In addition to nail unit melanocytic lesions, pigmentary changes in nail appearance may occur from trauma, inflammatory disease, occupational exposure and fungal infections among others. When it comes to melanocytic lesions, there is often hesitancy to biopsy due to concern for nail growth disruption or deformity afterward. In addition, nail biopsy specimens are often inadequate for pathologic diagnosis.
Accordingly, I would like to outline a stepwise approach to longitudinal melanonychia, including clinical evaluation and biopsy methods that together should aid in timely, accurate diagnosis.
Understanding The Causes And Ramifications Of Longitudinal Melanonychia
Longitudinal melanonychia is defined as deposition of melanin in the nail plate. Nail pigmentation often may not be melanocytic in origin. A short list of potential causes include:1
• nevi in the nail matrix, characterized by an increased number of melanocytes arranged in nests;
• matrix melanotic macule, which one would histologically see as an increase in the amount of melanin with or without hyperplasia;
• non-melanocytic nail tumors, such as squamous cell carcinoma;
• human immunodeficiency virus (HIV) infection;
• inflammatory nail disorders;
• endocrine disorders, such as Addison’s disease and Cushing’s disease; and/or
Aside from the fact that it may represent melanoma, why is longitudinal melanonychia so important for podiatric clinicians? In 2013, Bello and colleagues studied acral melanoma, defined as melanoma of the palms, soles and nail units, in order to answer the question as to whether this type of melanoma has a worse prognosis than melanoma elsewhere on the body.2 Prior to this study, only conventional wisdom supported that melanoma on the foot had a worse prognosis with no real data suggesting as such. This may have been due to a lack of examination of the foot or lesions hidden from view that resulted in diagnosis at later stages, and subsequently worse prognosis.
In the study, which included 170 volar and 111 nail unit melanomas, researchers reached the following conclusions:
“Acral melanoma tumors exhibit aggressive histopathologic features associated with a poorer survival outcome. Acral melanoma patients have an inferior survival (in comparison to those with non-acral melanoma tumors on the extremity) when matched for stage, perhaps reflecting inherent alterations in tumor biology.”2
These study conclusions obviously have serious implications for podiatrists from both the patient care and risk management perspectives.
Key Considerations In The Evaluation Of Longitudinal Melanonychia
Melanoma of the nail unit is relatively rare. Although it occurs equally in individuals with both darker and fairer skin, it is the most common type of melanoma in deeply pigmented individuals, and is mostly diagnosed between the ages of 40 and 70. A further complication is that in darker-skinned individuals, longitudinal melanonychia can commonly occur in one or multiple nails. This is often referred to as ethnic or racial pigmentation, and is mostly benign. The clinical presentation of pigmented streaks within the nail unit arising from benign versus malignant lesions is not as easy to differentiate as it is for melanoma elsewhere on the skin, where the well-known and well-taught “ABCDE” criteria for the most part is reliable.
The first step in the evaluation of longitudinal melanonychia is an overview of the lesion clinically. When should a presentation of longitudinal melanonychia result in a heightened index of suspicion? As per the classic text by Baran and Dauber, we should be suspicious of melanoma when a lesion of longitudinal melanonychia:3
1. begins in a single digit of a person during the sixth decade of life or later;
2. develops suddenly in a previously normal nail plate;
3. changes, including darkening or widening (especially at proximal end);
4. occurs in either the thumb, index finger, or hallux;
5. occurs attendant to a history of digital trauma;
6. occurs as a single band in the digit of a dark-skinned individual, especially if it is in the thumb or hallux;
7. appears with blurred as opposed to sharp lateral borders;
8. occurs in a patient with a prior history of melanoma;
9. occurs in a patient identified as having increased risk for developing melanoma, such as a patient with family history of melanoma or dysplastic nevus syndrome;
10. occurs with nail dystrophy, destruction or partial nail plate absence.
Levit and colleagues, after reviewing the world literature on subungual melanoma, developed a set of criteria for the clinical detection of subungual melanoma in an attempt to enable clinicians and the public to identify longitudinal melanonychias that are candidates for biopsy. The result was the “ABCDEF” algorithm of subungual melanoma.4
• A. Age: Range 20 to 90 years, peak fifth to seventh decade, African-American, Native American and Asian races.
• B. Band. Pigment is brown-black. Breadth is greater than or equal to three mm. Border is irregular or blurred.
• C. Change. Rapid increase in size or growth rate of band. This can also refer to a lack of change, namely failure of nail dystrophy to improve with treatment.
• D. Digit involved. The thumb is the most common digit involved followed by the hallux and index finger. A single digit is more worrisome than multiple digits. Dominant hand involvement is more common than that of a non-dominant hand.
• E. Extension. Extension of pigment on to the proximal or lateral nail fold (Hutchinson’s sign) or the free edge of the nail plate.
• F. Family or personal history. Previous history of melanoma or dysplastic nevus syndrome.
As far as I am concerned, any singular finding in the aforementioned lists by Baran and Dauber, and Levit and colleagues is reason enough to consider biopsy, even though we should strive to always make judgments based on a constellation of findings.3,4
What Is The Role Of Dermoscopy In Evaluating Longitudinal Melanonychia?
In addition to clinical examination and history, dermoscopy has become increasingly prevalent in the evaluation of pigmented nail unit lesions. Indeed, there is much defined criteria in the literature to guide clinicians with ever increasing levels of assurance in using dermoscopy to make decisions on whether biopsy is required or when one may observe a lesion for change. However, considerable controversy exists on the reliability of clinical examination and dermoscopy regarding melanonychia and the decision to biopsy or observe.
In a five-year observational study on the use of clinical exam and dermoscopy alone in the diagnosis of longitudinal melanonychia, Sawada and colleagues showed great accuracy in determining which lesions needed biopsy immediately (Type lll), which can be observed (Type l) and which should be observed at greater frequency (Type ll).5 In their series, no lesion was diagnosed beyond the curable in situ stage, leading to the conclusion that “dermoscopy of nail lesions can be very useful, and three months follow up for Type ll lesions (intermediate suspicion observed at greater frequency) to look for change is recommended.”5
In another study by Di Chiacchio and coworkers to assess the reliability of dermoscopy and clinical exam in nail pigmentation diagnosis, examiners were stratified into groups including students, residents, general dermatologists and dermatologists declaring expertise in nail diseases.6 Across all these groups, there was a high level, in the 50 percent range, of misdiagnosis, leading to the conclusion that: “overall accuracy of dermatologists in the diagnosis of nail matrix in-situ melanoma using dermoscopy and clinical criteria is low, confirming that biopsy is still the gold standard for diagnosis of these lesions.”6
These two diametrically opposed conclusions have significant obvious implications but rest assured, dermoscopy has been established as a very meaningful diagnostic tool, not only in nail pigmentation diagnosis but across the spectrum of skin, nail and hair diseases, whether they are infectious, inflammatory, vascular, benign or malignant. I believe that dermoscopy needs to become as routine as any other diagnostic method among podiatric clinicians. Training programs, texts, atlases and online resources are plentiful, but nothing replaces daily consistent use of the dermatoscope to further one’s learning.
Dermoscopic patterns of longitudinal melanonychia basically fall into two categories: regular and irregular. A regular dermoscopic pattern is characterized by a brown homogenous background band. The color of the individual lines within the band vary from tan to brown to black. The spacing between the lines in the band is regular and the lines in a regular pattern will have similar shades of brown. The thickness of the lines within a band of regular pattern should be relatively uniform and parallel (see first photo above).7
An irregular dermoscopic pattern also has a shade of brown pigmentation in the background. However, the color and thickness of the lines in the band vary as does the spacing between them. There may be disruption in parallelism with rapidly growing lesions and the entire width of the band may be wider proximally than distally (see second and third photos above).7
If any equivocation exists regarding dermoscopy findings, one should perform a biopsy. Logically, the more experienced the examiner, the greater the chance of the clinician doing the biopsy on firm clinical grounds, thus reducing the number of unnecessary biopsies. Although I abhor the term “unnecessary biopsy,” current and future health-care economic policies dictate that going forward, we must consider costs of care to remain competitive. However, the fact is that there is no commensurate legal reform protecting against increased exposure to litigation that is inevitable with intervention decisions based on cost efficiency. I have never seen anyone sued for doing a biopsy but many for not doing one.
Mastering The Technique For An Effective Nail Unit Biopsy
Once clinical evaluation and dermoscopy result in a decision to biopsy, many clinicians often ask, “What is the best technique for biopsy of longitudinal melanonychia?”
In the first place, these lesions are matrix-derived. Accordingly, nail plate tissue, clippings and subungual tissue cannot be diagnostic, and are not appropriate for diagnosis of longitudinal melanonychia. At best, these specimens will only reveal that melanin is present in the nail plate, leaving totally unanswered the question of what type of lesion it is coming from. The best biopsy specimen will be nail matrix tissue from the most proximal aspect of the band that is visible. If the band goes proximally under the proximal nail fold, then one must reflect the fold to reveal the most proximal aspect of the band.
At this point, the width of the band is then the most important parameter in making a decision on biopsy technique. While it is true that disruption of the nail matrix during the procedure may impact nail cosmesis afterward, the matrix, if handled properly, is actually very resilient and nail plate deformity is not a certainty.
For biopsy of longitudinal melanonychia, the following is generally agreed upon.
• Every presentation of longitudinal melanonychia should initially raise concern, certainly in Caucasians. However, in dark-skinned races, acral location of melanoma (not incidence) is more common and therefore especially important for podiatrists.
• Longitudinal melanonychia in children representing melanoma is very rare.
• Adequate tissue sampling and procedure choice depends on location and size of the pigmented band.
• Consideration of discomfort, cost, recovery time and resulting nail cosmesis also plays a role.
• Proximal nail matrix procedures are more sensitive to cosmetic disruption than distal matrix procedures.
• Any biopsy technique providing adequate sampling for diagnosis is acceptable.
• Three mm punch biopsy of distal matrix lesions less than three mm in width is shown to be adequate for sampling and cosmesis. Three mm punch biopsies for wider lesions risks sampling error and leaves lesion behind.
• The tangential matrix shave biopsy may be the procedure of choice for all but distal matrix lesions smaller than three mm.8
For distal matrix lesions just approaching three mm in width or less, a full-thickness three mm punch biopsy is a good biopsy technique. A defect of this size, for the most part, is fully recoverable and should not produce nail growth problems. However, one should relate this possibility to the patient (see fourth, fifth and sixth photos above).
What if the band is three mm or wider? At this point, we must consider a transverse or tangential shave biopsy of the matrix. The advantage of this technique is that it removes the entire lesion and affords greater sampling for pathologic analysis. One would confine the shave biopsy to the matrix epithelium only in order to avoid the deeper dermis of the matrix. As such, the matrix epithelium can easily regenerate over the dermis and not result in nail plate disruption.
In a transverse shave procedure, one reflects the proximal nail fold and removes the local area of nail plate. The visible white, glistening area is the nail matrix where the clinician performs the shave biopsy. The slice of tissue is so thin that one can actually see the 15-blade through it as one shaves the lesion free (see seventh photo above). Submit the removed nail plate with the matrix tissue specimen. At the end of the procedure, reapproximate the proximal fold and either suture in place or hold with wound closure strips. Some place a piece of foil or xeroform under the fold to prevent adherence and scarring of the fold to the matrix biopsy area. After removal of the matrix tissue, one should spread this tissue over a small piece of cardboard before placing it in formalin. Doing this prevents curling of the tissue upon itself, allowing proper access and processing in the pathology lab (see eighth photo above).
The shaved matrix tissue is very thin but studies document that it is thick enough to provide good sampling of the tissue.9 Should histology reveal a benign process, no further intervention is required. If there is a diagnosis of melanoma, the next step is wide local excision surgery, which may include wedge resection of the nail fold, en bloc resection of the nail apparatus with skin grafting, Mohs surgery or amputation. One makes this decision depending on the totality of the pathologic findings.
It is my hope that this short discussion on a stepwise approach to the evaluation and management of longitudinal melanonychia will stimulate increased attention to these lesions. Here are some key points to consider in diagnosing and managing longitudinal melanonychia.
• Acral melanoma or lesions suspected as such are unavoidable. These lesions are common in podiatric practice.
• Studies document a worse prognosis for acral melanoma than non-acral melanoma.
• Although the rarest subtype, acral melanoma is the most common type in dark-skinned individuals and has equal incidence among all races, placing the podiatric clinician on the front lines in the effort toward early diagnosis.
• Dermoscopy is now mainstream with ever increasing numbers and varieties of non-dermatology practitioners learning this technique.
• Clinicians see longitudinal melanonychia, the clinical expression of both benign and malignant nail matrix lesions, virtually every day in clinical practice.
• Biopsy management of longitudinal melanonychia can be in the skill set of every practicing podiatrist. At the very least, clinicians should perform a detailed clinical examination and if one chooses not to perform biopsy procedures, he or she should readily and regularly refer to a colleague who does.
Dr. Markinson is an Associate Professor in the Department of Orthopedic Surgery, an Instructor in the Department of Dermatologic Surgery and a Team Member of the Melanoma and Skin Cancer Program at the Tisch Cancer Institute of the Icahn School of Medicine at Mount Sinai Medical Center in New York.
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2. Bello, DM, Chou JF, Panageas KS, et al. Prognosis of acral melanoma: a series of 281 patients. Ann Surg Oncol. 2013:20(11):3618-3625.
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11. Rubin AI, Jellinek NJ, Daniel III CR, Scher RK. Sher and Daniel’s Nails: Diagnosis, Surgery, Therapy. 4th ed. New York;Springer:2018.