Table 1.

Differential diagnosis of TFFD

Diagnosis	Clinical manifestations	Histopathological features	Identifying features
Dermatitis neglecta	Adherent hyperpigmented papules, polygonal plaques, or verrucous lesions with poor hygiene	Hyperkeratosis, acanthosis, papillomatosis, and lamellar orthokeratosis	Hyperpigmented well-define cornflake-like waxy scales on dermoscopy Soap-water test is positive
Acanthosis nigricans	Hyperpigmented velvety plaques and increased skin markings over intertriginous areas	Hyperkeratosis, papillomatosis, minimal to no acanthosis, no hypermelanosis	Dark brownish clods with crista cutis on dermoscopy
Confluent and reticulated papillomatosis	Persistent erythematous to hyperpigmented scaly macules or papillomatous papules and coalescing confluent plaques distributed centrally and exhibiting a reticular pattern over the edges over upper trunk	Hyperkeratosis, papillomatosis with superficial dermal perivascular lymphocytic infiltration	Cobblestone pattern formed by polygonal flat-topped globules surrounded by whitish striae on dermoscopy
Dirty neck syndrome	Reticulate or rippled hyperpigmentation in patients with atopic dermatitis, predominantly involving the anterolateral aspects of the neck	Acanthosis, basement membrane thickening, epidermal hypermelanosis, dermal melanophages	Presence of other clinical features of atopic dermatitis
Postinflammatory hyperpigmentation	Hyperpigmented macules or patches over sites of healed inflammation	Epidermal or dermal melanosis
Icthyosis	Genodermatoses with impairment in keratinization	Icthyosis vulgaris: moderate hyperkeratosis hypogranulosis X-linked icthyosis: hyperkeratosis with hypergranulosis	Positive family history
Intertriginous granular parakeratosis	Hyperpigmented hyperkeratotic papules and coalescing plaques over intertriginous areas	Acanthosis, hyperparakeratosis and papillomatosis, with basophilic keratohyalin granules
Verrucous epidermal nevus	Congenital to early-acquired fleshy-to-brown, papillomatous papules and coalescing plaques, along Blaschko’s lines	Acanthosis, hyperkeratosis, papillomatosis, and epidermolytic hyperkeratosis	Thick brown branched lines and circles, terminal hairs with dotted vessels on dermoscopy
Frictional melanosis	Hyperpigmented patches over bony sites and friction-prone regions	Epidermal hypermelanosis, dermal melanophages	Brownish structureless zones in reticular pattern on dermoscopy
Macular amyloidosis	Pruritic hyperpigmented patches in ripple-like patterns over extremities and upper back	Basal layer hyperpigmentation. Globular deposits of amyloid material in papillary dermis and melanophages	Central brown to white hub at the center with brown fine radiating streaks, leafy projections, and dots on dermoscopy
Tinea versicolor (pigmented pityriasis versicolor)	Discreet to coalescent brown, hyperkeratotic scaly patches over head and neck	Orthohyperkeratosis and budding spores in stratum corneum with silent dermis	Yellow-green fluorescence on wood lamp
Ashy dermatosis	Round to oval ashy-colored hyperpigmented macules symmetrically involving the trunk	Lichenoid infiltration with macrophages	Irregular brown-grey linear dots and globules over pinkish-brown background. Irregular linear vascular pattern on dermoscopy
Dowling–Degos syndrome	Genodermatosis with macular or papular folliculocentric lesions. Arrangement of lesion in a lacy or reticular pattern predominantly over folds	Elongated or branched rete ridges having increased melanin deposition over the tips. Suprapapillary epithelium sparing	Irregular brownish projections around central hypopigmented, indicative of follicular epithelium on dermoscopy
Acroangiodermatitis of Mali	Purplish-blue to brown papules and plaques located on the medial and lateral malleoli	Hyperparakeratosis, epidermal hyperplasia, pseudo-sarcomatous capillary proliferation, and perivascular inflammation in the dermis, with extravasated red blood cells and hemosiderin deposits	Red or blue lacunae, white rail lines, with whitish veil along with scattered hemorrhagic crusts over a pinkish background on dermoscopy
Epidermolytic hyperkeratosis of the nipple and areola	Warty, hyperpigmented papules or plaques on the nipple and/or areola	Orthohyperkeratosis, filiform acanthosis, papillomatosis, and keratin plugging, hyperpigmented rete ridges, and a dermal lymphocytic infiltrate	Whitish papillomatous surface with white scales and brown hyperkeratotic deposits distributed on the cristae on dermoscopy
Scalp discoloration from selenium sulfide shampoo	Red-brown discoloration of scalp skin and appendages with/without desquamation	Pigment deposit within keratotic debris and parahyperkeratosis	Suggestive clinical history