Correlation of dermoscopic structures on nails
Diagnosis of pigmentation of the nail unit is challenging as the differential diagnosis is broad. It includes trauma, infection, exogenous pigmentation and melanocytic activation (lentigo, drug-induced, post inflammatory pigmentation) or proliferation (nevus, melanocytic hyperplasia or melanoma (Alessandrini et al., 2017; Braun et al., 2007; “dermoscopedia,” n.d.).
Gray band
In pigmented nail bands (longitudinal melanonychia), the presence of gray granules within a gray band correlates with epithelial hyperpigmentation due to melanocytic activation.
Brown band
Brown/black granules within a brown or black band reveals on the histopathologic study a melanocytic proliferation (Braun et al., 2007).
Irregular brown band
In melanocytic proliferations, an irregular pigmented band originating from the proximal nail fold with multiple colors, variable thickness of the lines and loss of parallelism is suggestive of nail apparatus melanoma (NAM) (Braun et al., 2007).
Micro-Hutchison’s sign
is the periungual skin pigmentation of hyponychium (pigmentation of the cuticle) evident only with dermoscopy (Braun et al., 2007). It is associated with NAM in adults and corresponds to the initial radial growth of melanoma into adjacent tissue. Histologically, it may reflect the Breslow index, as micro-Hutchinson sign has been seen associated with early melanoma (Starace et al., 2018).
Vascular polymorphism
showing different types of vessels on dermoscopy, reflects chaotic neoangiogenesis on histology and has been associated with the invasive stage of NAM (Starace et al., 2018)
Free edge dermoscopy
Dermoscopy can also guide biopsy by evaluating the free edge of the nail, avoiding inadequate sampling and delayed diagnosis.
Pigmentation of the upper part of the nail´s free edge
correlates histologically with melanocytic proliferations located in the proximal portion of the nail matrix. P
Pigmentation of the lower part of the nail´s free edge
correlates histologically with melanocytes proliferating distally in the nail matrix (Braun et al., 2006).
Intra operative in vivo dermoscopy of the nail matrix
Dermoscopy can be used as an intraoperative procedure to see the pattern of pigmentation of nail matrix and to select the most appropriate area to biopsy. Dermoscopy of the nail matrix reveals dermoscopic features not seen in the nail plate (Hirata et al., 2006, 2011). There are 4 dermoscopic patterns:
Regular gray pattern (fine regular grayish lines)
corresponding with pigmentation in the basal layer (melanocytic activation) and absence of melanocytic hyperplasia or nests.
Regular brown pattern (regular brown lines)
that histologically corresponds to benign melanocytic hyperplasia with larger amount of melanin and absence of melanocytic nests.
Regular brown pattern with globules or blotches
(regular longitudinal brown lines and presence of globules or blotches of regular size and distribution) is associated with melanocytic nevi. Histologically, the globules correlate with the presence of nests. The blotches correlate with the presence of large amounts of melanin.
Irregular pattern
(longitudinal lines of irregular color and thickness, with or without irregular globules or blotches), histologically correspond to a disorganized proliferation of atypical melanocytes with atypical cell nests. The irregular lines reveal atypical melanocyte proliferation producing thick longitudinal lines with spread of the pigmentation to adjacent areas. The irregular pattern shows a high sensitivity and specificity for melanoma (Hirata et al., 2011).
