Table 6.

Histopathological features in melanonychia

Cause of melanonychia	Histopathological features
Melanocytic activation	Epithelial hyperpigmentation,
	Normal melanocytic number and structure (4-9 mm interval or 200 mm2), Dendritic melanocytes,
	Scattered melanophages,
	No mitosis
Lentigo	Increased melanocytes (10-31 mm segment) with abnormal location,
	Full-thickness pigmentation in matrix epithelium and nail plate,
	Dendritic melanocytes,
	Mild cytological atypia,
	Few melanophages,
	No cell nests and suprabasal melanocytes.
	No epithelial hyperplasia and pagetoid spread in matrix
Melanocytic nevus	Junctional nevus with lentiginous pattern,
	Melanocytic proliferation,
	Irregular or slightly confluent cell nests.
	Suprabasal pagetoid spread,
	Mild nuclear pleomorphism,
	Minimal cytological atypia, dermal inflammation, and nail plate involvement
In-situ melanoma	Infiltrative edge,
	Increased melanocyte proliferation and suprabasal melanocytes,
	Irregular distribution and asymmetry of melanocytes,
	Tendency of fusion in nests and epidermal consumption,
	Cytological atypia,
	Dermal lymphoid cell infiltration
Invasive melanoma	Atypical melanocytic proliferation (39-136/mm),
	Irregular distribution of melanocytes,
	Confluent and irregularly dispersed cell nests with suprabasal scatter,
	Cytological atypia,
	Increased mitosis,
	Lymphocytic infiltrate and anisodendrocytosis