Two recent articles in the Archives of Dermatology serve as a reminder that melanoma may occur under the finger nail in the nail matrix.
The first one (full references for both below) used slides and prepared information from 12 cases to “test” dermatologist. Here is one of the examples given in the paper:
Nevus. A, Clinical features; B, nail plate dermoscopy; C, intraoperative dermoscopy. ABCDEF rule information: A (age, 35 years), C (change in band at 2 years; it became enlarged or darker), D (digit, third finger, right hand), and F (no family or personal history of melanoma)
Only 46-55% made the correct diagnosis of nail matrix melanoma in situ in this study. The level of expertise did not statistically influence the correct diagnosis.
Early diagnosis of melanoma of the nail unit is challenging. The tumor most often presents with a longitudinal nail pigmentation (longitudinal melanonychia), but this is not a specific sign for melanoma.
Longitudinal melanonychia can also be caused by numerous nonmalignant conditions that include nevi of the nail matrix, benign melanocytic hyperplasia (nail matrix lentigo), and a number of inflammatory, traumatic, or iatrogenic nail disorders that induce the activation of the nail matrix melanocytes.
Features on clinical examination that are suggestive but not pathognomonic of melanoma include inhomogeneous pigmentation with bands or lines of different colors, presence of nail plate fissuring or splitting, rapid enlargement of the band, a proximal part of the band that is broader than the distal (triangular shape), blurred lateral borders, and pigmentation of the periungueal skin.
These features have been summarized in the ABCDEF rule for diagnosis of nail melanoma and may help clinicians in distinguishing "nonalarming" from "alarming" bands. Each letter indicates features that are associated with an increased risk of melanoma:
- A (age as peak incidence of nail melanoma is between 50 and 70 years. A also reminds us of most commonly affected races: African Americans, Asians, and Native Americans).
- B (band: black to brown, breadth > than 3 mm, blurred borders)
- C (change: enlarging or darkening)
- D (digit: most fingernail melanomas affect the dominant hand)
- E (extension of the pigmentation to the surrounding tissues)
- F (family or personal history of melanoma)
The second one reminds us that melanoma in the nail matrix location (nail apparatus melanoma or NAM) is associated with a poor prognosis, mainly because of a delay in diagnosis. Too often diagnosed at an invasive stage. The authors note this is particularly true in cases involving amelanotic melanoma. They report 3 cases of in situ amelanotic melanoma with clinical lichenoid features, concluding that chronic unexplained monodactylic nail dystrophy should be investigated histologically.
All three of their patients (ages 39 to 60 yrs) presented with nail alterations characterized by lichenoid changes with longitudinal striation, distal splitting, and nail plate atrophy. Histologic examination revealed in situ amelanotic melanoma extending from the proximal matrix up to the distal part of the nail bed. (photo from article)
The authors give us the background on amelanotic NAM:
Amelanotic NAM represents 20% to 30% of ungual melanoma cases compared with less than 7% of the other cutaneous melanomas.
It usually presents as a chronic paronychia, a torpid granulomatous ulceration, a wartlike keratotic tumor, or a pyogenic granuloma.
It is usually located in the periungual folds or in the nail bed.
Clinical misdiagnosis, which is particularly frequent in amelanotic melanoma, is responsible for a delay in diagnosis as well as a poor prognosis.
Dermatologists' Accuracy in Early Diagnosis of Melanoma of the Nail Matrix; Nilton Di Chiacchio; Sergio Henrique Hirata; Mauro Yoshiaki Enokihara; Nilceo S. Michalany; Gabriella Fabbrocini; Antonella Tosti; Arch Dermatol. 2010;146(4):382-387.
In Situ Amelanotic Melanoma of the Nail Unit Mimicking Lichen Planus: Report of 3 Cases; Josette André; Isabelle Moulonguet; Sophie Goettmann-Bonvallot; Arch Dermatol. 2010;146(4):418-421.