Dermoscopic examination of nail pigmentation.

BACKGROUND: Diagnosis of longitudinal melanonychia is usually difficult, and neither a single clinical criterion nor a combination of symptoms currently can be used to clearly distinguish malignant from benign bandlike pigmented nail lesions. Biopsy is painful and often leaves definitive dystrophic scars.

OBJECTIVES: To describe and evaluate dermoscopic patterns associated with longitudinal nail pigmentation.

PATIENTS AND METHODS: A total of 148 unselected consecutive cases of longitudinal melanonychia were included over a period of 4 years (20 melanoma, 37 nevi, 16 drug-induced nail pigmentation, 45 nail apparatus lentigo of various types, 8 ethnic-type nail pigmentation, and 22 subungual hemorrhages). All patients were recruited from the dermatology unit outpatient clinic of the Hôtel Dieu de Lyon. All cases were photographed in vivo under oil immersion (dermoscopy). Patterns were recorded prior to final pathologic diagnosis. An independent biostatistics unit performed statistical evaluation using 7 semiologic patterns.

RESULTS: Melanoma cases were significantly associated with a brown coloration of the background and the presence of irregular longitudinal lines (P =.001). Blood spots were mostly observed in subungual hemorrhages (P =.001); however, their presence could not rule out melanoma. Micro-Hutchinson sign was observed only in melanoma, but its rare occurrence did not allow any statistical evaluation of its specificity. Nail apparatus nevi were significantly associated with a brown coloration of the background and the presence of regular lines (P =.001). Nail apparatus lentigo, ethnic-type pigmentation, and drug-induced pigmentation were significantly associated with homogeneous longitudinal thin gray lines and gray coloration of the background (P =.001). Microscopic longitudinal grooves were unspecific, occurred in several conditions, and were associated with any type of ungual discoloration.

CONCLUSIONS: We believe that dermoscopic examination of the nail plate in cases of longitudinal melanonychia provides useful information that could help clinicians to more accurately decide if a nail apparatus biopsy should be performed; however, histopathologic diagnosis remains the gold standard in doubtful cases.