Melanonychia: Clues for Diagnosis and the Importance of Histology

2) A micro Hutchinson sign, or pigmentation of the proximal nail fold that can be appreciated only on dermoscopy.

On the other hand, melanocyte activation typically presents as a faint gray, longitudinal streak. Melanocyte activation is common in pregnant women and can also occur in the setting of onychomycosis. Other dermoscopy patterns include multicolored round blotches, which corresponds to subungual hemorrhage, and diffuse brown or regular lines of brown pigment seen in both nevi and lentigenes. The final dermoscopy pattern seen in nails is irregular grooves in the nail plate which can be seen in benign pigmented lesions and melanoma.

There are times melanonychia is so egregious that it can only be melanoma. A wide, deeply pigmented band with irregular lines and pigmented extension onto the periungual tissues is nearly pathognomonic for melanoma. While it is still important to make sure those cases are biopsied appropriately in the nail matrix and sent for evaluation with experienced dermatopathologists, these are not the cases that serve as a diagnostic challenge. What is concerning is many cases of subungual melanoma look very subtle clinically. Dr. Jellinek provided numerous clinical images of biopsy proven lentigines and nevi as well as melanomas that clinically appear surprisingly similar (See Figure 1). He advised that even with excellent dermoscopy skills and knowledge of nail lesions, ultimately a biopsy is required to make the correct diagnosis. It is critical to recognize when the diagnosis cannot be made clinically or even if there is uncertainty. He argues, there should be a lot of uncertainty due to subtle presentation of earlier subungual melanomas.

Dermoscopy shines for subungual hemorrhage

Subungual hemorrhage is a common benign cause of longitudinal melanonychia and can mimic melanoma to the untrained eye. Dermoscopy shines to diagnose subungual hemorrhage because of the unique features that are often seen. Specific features of hemorrhage include smudged purple or brown blood spots, round proximal shape, filamentous distal shape, and importantly, the lack of background color with linear streaks of pigment. Importantly, as the nail grows, the hemorrhage will spare the proximal nail since the blood is trapped on the ventral surface of the nail plate. In early hemorrhage, it can be more difficult to be certain, and longitudinal follow up of the nail is helpful to see it grow out. Dr. Jellinek recommends photographing all cases of suspected subungual hemorrhage and follow up to ensure it is resolving as expected.

When to worry more

In a review of his personal clinical cases, Dr. Jellinek reviewed images of melanonychia in patients of different phototypes and ages that seemed strikingly similar clinically with very similar dermoscopic features that ultimately had very different histologic findings. Thin pigmented lesions in young patients can still be melanomas, and performing a biopsy is important. However, there are some features that will make you worry more for a malignant cause of melanonychia:

• • Worry more with wider bands of longitudinal pigment (>2-3mm) is more worrisome, especially in older patients (>65). However, less than 1mm does not get you off the hook!
  • Worry more with a solitary pigmented band (i.e. only one nail is involved).
  • Worry more with pigment drop out. This refers to areas within the longitudinal band that lack pigment (i.e. streaks of background nail color within the pigmented band).
  • Worry more in older patients. However, not all cases of pediatric melanonychia are benign.
  • Worry more when you see the triangle sign (i.e., when the pigment is broader proximally than distally). This can be a sign of proliferation.
  • Worry more if there is pigment on the periungual skin. Close examination of the skin of the entire affected digit is necessary for evaluation of melanonychia.

So how do you decide how to manage melanonychia? Dr. Jellinek states there are really three possible assessments: some cases are clearly only appropriate for a biopsy, others have enough reassuring features to photo document and monitor (e.g., multiple pigmented nails, classic activation or hemorrhage appearance), and finally, there are all of the cases that fall in the gray zone and cannot be diagnosed clinically. It is important to recognize when you don’t know. It can be helpful to seek a second opinion, but ultimately if there is any uncertainty, a biopsy should be performed. It is important that biopsies are not deferred due to discomfort with nail procedures.  Furthermore, biopsies must be performed on the appropriate location (matrix) and provide an adequate tissue sampling for the dermatopathologist.  In most instances, the ideal biopsy technique is the matrix shave (tangential excision).