| Selected disorders | Key histopathologic findings |
| Acanthosis nigricans | - Hyperkeratosis and papillomatosis of the epidermis
- Basal layer hyperpigmentation
- Minimal acanthosis (misnomer)
|
| Actinic lichen planus | - Variable with typical findings of lichen planus including hyperkeratosis without parakeratosis, hypergranulosis, irregular acanthosis with "saw-toothed" rete ridges, liquefaction degeneration of the basal layer, and band-like lymphocytic infiltrate at the dermal-epidermal junction
|
| Addison's disease[1] | - Increased basal layer melanin, sometimes melanin incontinence
|
| Becker's melanosis[2] | - Variable papillomatosis, acanthosis, and hyperkeratosis
- Regular elongation of the rete ridges with or without pilosebaceous unit hyperplasia
- May have increased hair follicles or smooth muscle
|
| Café-au-lait macules[1] | - Increased melanin in the basal layer
- Normal number of hyperactive melanocytes
|
| Dermal melanocytosis[1] | - Spindle-shaped dendritic melanocytes in the deep dermis with abundant fine granules of melanin
|
| Diabetes mellitus - diabetic dermopathy[1] | - Dermal hemosiderin, increased papillary dermal blood vessels, sparse perivascular lymphocytes
|
| Diabetes mellitus - necrobiosis lipoidica | - Diffuse palisaded and interstitial granulomatous dermatitis with tiers of granulomatous inflammation (includes multinucleated histiocytes) aligned parallel to the surface
|
| Dowling-Degos | - Delicate, elongated, hyperpigmented rete ridges
- Sometimes resembles a reticulated seborrheic keratosis
|
| Drug-induced hyperpigmentation[1] | - Variable depending on drug or chemical:
- Minocycline: brown dermal pigment that is positive with iron and melanin stains
- Gold: chrysiasis pigment appears as black particles
- Bleomycin: basal layer with increased melanin
- Clofazimine: brown lipofuscin that stains with PAS
- Amiodarone: brown pigment that stains with PAS
|
| Ephelides[1] | - Increased melanin in basal layer
- Normal or decreased number of hyperactive melanocytes
|
| Erythema dyschromicum perstans[1] | - Liquefaction degeneration of the basal layer
- Melanin incontinence
- Interface changes with perivascular or interface lymphocytes
|
| Erythromelanosis follicularis faciei et colli[3] | - Hyperkeratosis
- Dilatation of superficial dermal blood vessels
- Follicular plugging
- Variable melanin in basal layer
|
| Exogenous ochronosis[1] | - Yellow-brown "banana-shaped" deposits on homogenized collagen bundles
- Small yellow-brown granules in endothelial cells and sweat glands
|
| Hemochromatosis[1] | - Increased melanin in the basal layer
- Hemosiderin deposits scattered in the dermis, usually around blood vessels and sweat glands, best seen with Perl's stain
|
| Lentigines[1] | - Hyperpigmented, often elongated rete ridges, usually with increased melanocytes
|
| Lichen planus pigmentosus | - Similar to erythema dyschromicum perstans with marked pigment incontinence and epidermal atrophy
|
| Melasma[4] | - Increased melanin deposition in all layers of the epidermis
- Solar elastosis
- More abundant mast cells
|
| Nevus of Ota, Nevus of Ito, Hori's nevi[1] | - Normal epidermis
- Spindle-shaped dendritic melanocytes in the dermis with abundant fine granules of melanin
|
| Nevus spilus | - Lentiginous melanocytic hyperplasia
- Papular foci represent junctional, compound, blue, Spitz, and/or atypical nevi
|
| Periorbital hyperpigmentation[5,6] | - Dermal melanocytosis and melanin in upper dermal macrophages (melanophages)
|
| Post-chikungunya pigmentation[7,8] | - Intact basal layer with diffuse hypermelanosis of the entire epidermis
|
| Postinflammatory hyperpigmentation | - Increased or normal amount of melanin at basal layer, with or without melanin incontinence based on etiology
|
| Primary cutaneous amyloidosis[1] | - Macular amyloidosis with subtle amyloid globules in the papillary dermis in areas of melanin incontinence
- Lichen amyloidosis with small deposits of amyloid in the dermal papillae
|
| Riehl's melanosis[1] | - Lymphocytic perivascular or interface dermatitis with melanin incontinence
|
| Smoker's melanosis | - Mucosal surface with basal layer melanosis, with or without melanin incontinence
|
| Terra firma-forme dermatosis[9] | - Prominent lamellar hyperkeratosis with focal areas having compact orthokeratosis in whorls
|
