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- Presentation
Dermoscopy and Clinical Diagnosis of Nail Unit Pigmented Lesions
Description
The talk reviews dermoscopic and clinical diagnosis of pigmented nail unit lesions, emphasizing that the first step is determining whether a lesion originates from the lunula/matrix or elsewhere in the nail unit. If it does not arise from the matrix, common considerations include subungual hemorrhage, fungus, glomus tumor, and pyogenic granuloma. Hemorrhage is recognized by blood spots, a homogeneous maroon area, and distal filamentous patterns, but clinicians must ensure nothing lies beneath the blood; a normal free edge without pigment supports hemorrhage, while follow-up can show blood growing distally. Onychomycosis tends to produce cloudy white-yellow discoloration with a jagged proximal edge and, when pigmented, a triangle with its base distally. Glomus tumors usually present with bluish hue, pain, possible nail dystrophy, and can be supported by cold sensitivity and other clinical tests, while dermoscopy is limited except intraoperatively. Pyogenic granulomas can destroy the nail plate and often require biopsy to exclude melanoma. If the lesion does arise from the matrix, the lecture distinguishes distal matrix lesions, which pigment the undersurface of the nail plate, from proximal matrix lesions, which pigment the top surface; the free edge is therefore critical for localization. Onychomatricoma shows nail thickening, leukonychia/xanthonychia, splinter hemorrhages, and a honeycomb-like free-edge pattern. Onychopapilloma and early squamous cell carcinoma may look similar initially, with leukonychia, xanthonychia, splinter hemorrhages, V-shaped nicking, and subungual keratin; multiple onychopapillomas should prompt consideration of BAP1 germline mutation and cancer screening. For melanocytic lesions, the key distinction is activation versus proliferation. Melanocytic activation produces homogeneous gray-tan bands without discrete striations and is associated with conditions such as ethnic pigmentation, drug effects, trauma, and post-inflammatory change. Benign nevi typically show an organized pattern with regular, parallel, evenly spaced brown lines, whereas melanoma shows disorganization, irregular spacing, loss of parallelism, multiple colors, and sometimes granular pigmentation or increasing pigment over follow-up. Clinical red flags outweigh dermoscopy: a very wide band, Hutchinson sign, triangular widening proximally, and nail dystrophy should trigger biopsy regardless of dermoscopic appearance. Hutchinson sign includes pigmentation of the eponychium or hyponychium, and micro-Hutchinson sign is only visible with dermoscopy. Congenital nail nevi are a major exception because they often look alarming and cannot be reliably classified by usual rules; they may show a fibrillar pattern and are generally monitored rather than aggressively biopsied. The lecture concludes that correct diagnosis depends on integrating clinical clues, free-edge examination, dermoscopy, and biopsy site selection, illustrated by a case where prior biopsy was done at the wrong matrix site and onycholysis helped reveal the error.
View moreConclusions
- When a pigmented nail band does not arise from the lunula, hemorrhage, fungus, glomus tumor, and pyogenic granuloma are the main alternatives, and free-edge or clinical evolution can help distinguish them from melanocytic disease.
- If a band arises from the lunula, the key next step is to decide whether it reflects melanocytic activation, melanocytic proliferation, or a non-melanocytic lesion such as onychomatricoma or onychopapilloma.
- Clinical red flags like a wide band, Hutchinson sign, triangular widening proximally, or nail dystrophy outweigh dermoscopic reassurance and should prompt biopsy to exclude melanoma.
- A homogeneous gray or tan longitudinal band with little visible internal striation is more consistent with melanocytic activation, lentigo, ethnic pigmentation, or drug-related pigmentation than with melanoma.
- A regular brown band with parallel, evenly spaced, similar-thickness lines is most consistent with a benign nail matrix nevus.
- An irregular brown band with disrupted parallelism, variable spacing or thickness, asymmetry, or more than two colors is strongly suggestive of melanoma.
- Granular pigmentation, new colors, and increasing pigmentation during follow-up favor melanoma, whereas decreasing pigmentation supports a benign lesion.
- Onychomatricoma is suggested by nail plate thickening, leukonychia or xanthonychia, splinter hemorrhages, and a honeycomb pattern at the free edge.
- Onychopapilloma and early squamous cell carcinoma can look similar initially, but persistence without change favors onychopapilloma while evolution suggests carcinoma.
- Multiple onychopapillomas should raise suspicion for BAP1 tumor predisposition syndrome and justify consideration of genetic testing and cancer screening.
- Dermoscopy is especially useful for identifying the free-edge distribution of pigment, which helps determine whether a lesion originates from the distal matrix or proximal matrix.
- Pigment on the bottom surface of the free edge indicates a distal matrix source, while pigment on the top surface indicates a proximal matrix source.
- Nail unit melanoma can be missed if biopsy is taken from the wrong matrix compartment, so dermoscopic localization is critical for choosing the correct biopsy site.
- Congenital nail matrix nevi often mimic melanoma clinically and dermoscopically, so adult rules cannot reliably distinguish them from malignant lesions.
- In children, longitudinal melanonychia behaves unpredictably and cannot be safely classified using adult algorithms, so careful follow-up is preferred over overconfidence in morphology.
- Overall, the safest approach to suspicious nail pigmentation is to prioritize clinical warning signs, then use dermoscopy and free-edge examination to localize the lesion and decide on biopsy or monitoring.
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