NEW YORK End-on dermoscopy is an invaluable tool in making an accurate diagnosis in patients who present with dark streaks in the nails of their fingers or toes, Dr. Nathaniel Jellinek said at the American Academy of Dermatology's Academy 2007 meeting.
Because the dorsal nail plate is produced by the proximal nail matrix, and the ventral plate is produced by the distal matrix, an end-on dermoscopic view of the patient's nails can provide something of a map of the nail, indicating the points from which the pigment is emanating (J. Am. Acad. Dermatol. 2006;55:5123). This can be a helpful guide as to where and when to biopsy, said Dr. Jellinek of the department of dermatology, Brown University, Providence, R.I.
The real value of end-on dermoscopy is not so much that it leads to a definite diagnosis in and of itself, but that it can tell you where you need to look when taking a biopsy, he said. It helps you zero in on the lesion location.
Dorsal pigmentation points to a proximal matrix lesion, whereas pigmentation of the ventral aspect of the nail plate points to distal lesions. "You still have to biopsy if you are not sure what you're looking at," Dr. Jellinek said.
Nail biopsies, however, are tricky. Small biopsies in the setting of a large lesion run the risk of missing something important, but larger full-thickness biopsies (greater than 3 mm) increase the risk of permanent dystrophy, particularly of the proximal matrix. This can lead to permanent split nails.
Dr. Jellinek outlined his published algorithmic approach for assessing and evaluating longitudinal melanonychia. If the lesion seems to be in the distal nail matrix and measures 3 mm or less, a 3-mm punch biopsy is adequate and safe. If the lesion is larger than 3 mm, however, a newer techniquethe matrix shave biopsymay be a better option (J. Amer. Acad. Dermatol. 2007;56:80310).
Any proximal matrix lesion can be handled elegantly by the matrix shave biopsy. "Done right, there's minimal risk of nail dystrophy," he said of the shave technique. Any lesion of the lateral aspects of the nail unit should be handled by lateral longitudinal excision.
Longitudinal brown or black streaks on a nail present a diagnostic challenge. In most cases, the underlying etiology is benign, but in some, these streaks can signal the presence of nail melanoma.
The first diagnostic step is to consider the patient's age and overall cutaneous appearance, according to Dr. Jellinek. Melanomas are extremely rare in children and younger adolescents; this is reassuring but certainly not an absolute finding, and each patient must be evaluated on a case-by-case basis. Furthermore, "always look at the patient's whole skin. It can provide a lot of clues," Dr. Jellinek added. Then, go to dermoscopy and end-on dermoscopy, preferably using a water-soluble medium.
The observable diagnostic features of melanocytic nevi on dermoscopy include brown, longitudinal pigmentation with smooth, parallel lines and consistent thickness. Brown pigmentation overlaid by longitudinal lines showing irregularity of thickness, spacing, or alignment are suggestive of melanoma (Dermatol. Ther. 2007;20:310).
Grayish bands without any brown stripes are suggestive of lentigines or other types of melanocytic activation, and are much less suggestive of melanoma. Round-shaped black spots are generally blood spots under the nail plate, indicative of injury but not neoplasia. It is important to note that the presence of blood does not rule out an underlying neoplasm (J. Am. Acad. Dermatol. 2007;57:176).
Although most physicians notice brown streaks on a patient's nails, and quickly jump into a work-up to rule out malignant melanoma, many overlook cases of erythronychia, or red streaks in the nail plate. "It's underrecognized in our clinics. I'm seeing red bands in the nails at least once a week," Dr. Jellinek said.
These lesions almost always involve the distal nail matrix, and although they are usually innocuous, this is not always the case.
The real worry is squamous cell carcinoma, which is, fortunately, rare in the nail bed, he noted. If the red streak is on only one nail and is long standing, then it is probably stable and not neoplastic.
Dermoscopy of the left great toenail (left) shows a longitudinal band with parallel brown lines. With end-on dermoscopy, the pigment maps to the ventral surface of the nail plate's free edge (arrow). PHOTOS COURTESY DR. NATHANIEL JELLINEK
