Table 4.

Differential diagnosis of FAN

Characteristics	Facial acanthosis nigricans (FAN)	Maturational hyperpigmentation (MH)	Melasma	Exogenous oochronosis	Lichen planus pigmentosus
Clinical features	Brown to black macular pigmentation with blurred ill-defined margins areas having varying degrees of textural changes	The texture of MH smoother than FAN	Symmetric progressive hyperpigmentation of the facial skin that has a predilection for darker skin phenotypes	Deposition of microscopic, ochre-colored pigment in the dermis, giving rise to a blue-black hue in the skin	Focal or diffuse gray-blue or dark brown macules on exposed areas
Dermoscopy	Multiple cristae and sulci with hyperpigmented dots in cristae cutis	Perifollicular rings of hyperpigmentation	Light brown-to-dark brown pigmentation, dark brown-colored globules/dots/blotches, pseudoreticular pigmentation with diffuse dark brown-to-grayish pigmentation with sparing of follicular openings	Dark hyperpigmentation, blue-gray dots and globules with a caviar-like appearance, obliteration of follicular opening Elongated and curvilinear worm-like structures conjoined together in a reticulate pattern of ochronosis	Blue-gray pigmentation, slate gray dots with regular distribution of pigment seen, hem-like pattern in a typical case, especially in nonfacial lesions
Histopathology	Hyperkeratosis and hypermelanization of the basal layer with variable degrees of acanthosis and papillomatosis	Minimal to nil hyperkeratosis and papillomatosis and moderate to dense basal layer hypermelanization	Solar elastosis, increased melanin concentration, epidermal flattening, and dermal lymphomononuclear inflammation	Pigment incontinence, solar elastosis, ochre pigment, “banana-shaped” fibers in papillary dermis, and eventually degeneration of the collagen; colloid milium and/or granulomas	Atrophy of the dermis with loss of rete pattern, focal basal cell vacuolization, and sparse dermal infiltrate