Differentials
Epidermal naevus
SIGNS / SYMPTOMS
Usually presents in children on the neck, torso, and extremities rather than the flexural and intertriginous areas typically involved by acanthosis nigricans (AN).[26] Lesions may be linear or verrucous in appearance.
INVESTIGATIONS
Skin biopsy shows variable degrees of epidermal hyperplasia, papillomatosis, and inflammation.
Some cases may show features indistinguishable from AN, but there is typically less papillomatosis and more inflammation than seen in AN.[26]
As some authors consider AN a type of epidermal naevus, the distinction may be academic in some cases.[26][27]
Dowling-Degos disease (reticular pigmented flexural anomaly)
SIGNS / SYMPTOMS
Lesions with reticulated pattern in flexural areas.[28]
Lesions do not appear thickened and velvety, in contrast with acanthosis nigricans (AN).
Patients may also have lesions on the hands and feet and palmoplantar pitting.[28]
INVESTIGATIONS
Skin biopsy shows filiform downgrowths of epidermis with pigmented rete ridges and occasional pseudohorn cysts, resembling seborrhoeic keratosis.
Papillomatosis and hyperkeratosis resembling AN are not seen.[28]
Confluent and reticulated papillomatosis (of Gougerot and Carteaud)
SIGNS / SYMPTOMS
Red/brown verrucous-appearing papules with central confluence and peripheral reticulate pattern.[29]
Typically presents on the central chest or back, not flexural areas as in acanthosis nigricans (AN).[30]
INVESTIGATIONS
Skin biopsy shows epidermal acanthosis and low papillomatosis (less prominent than AN), and may show basilar pigmentation.[29]
There may also be mild telangiectasia and beading of elastic fibres; findings not seen in AN.
Seborrhoeic keratosis
SIGNS / SYMPTOMS
Common lesion in adults that usually present as one or a few well-defined pigmented papules on the chest, back, and face.
Most lesions are small, although rare plaque-like lesions have been reported on the buttocks or thighs.
INVESTIGATIONS
Skin biopsy shows epidermal acanthosis with pseudohorn cysts and variable papillomatosis. The lesions are usually more endophytic than acanthosis nigricans (AN), and the papillomatosis is more irregular.
There is often inflammation and associated squamous differentiation with eddies, findings not seen in AN.
Mycosis fungoides
SIGNS / SYMPTOMS
Long-standing patches and plaques in bathing-trunk distribution, typically not velvety or clinically pigmented.[31]
Rare presentation may mimic acanthosis nigricans clinically.[32]
INVESTIGATIONS
Skin biopsy shows epidermotropism by enlarged, atypical lymphocytes, often with nuclear hyperchromasia and hyperconvolutions.
Immunohistochemistry shows an increased CD4:CD8 ratio in most cases. Molecular analysis shows clonal T-cell gene re-arrangement.[31]
Lichen simplex chronicus/eczematous dermatitis
SIGNS / SYMPTOMS
Hyperpigmented, lichenified plaques resulting from excessive scratching or rubbing of skin.
Often very pruritic.
Common sites include posterior neck, as in acanthosis nigricans, and extremities.
INVESTIGATIONS
Clinical features sufficient to distinguish these entities without further investigation.
Ichthyosis hystrix
SIGNS / SYMPTOMS
Generalised hyperkeratosis often with hyperpigmented verrucous surface.[33]
This can resemble familial, benign acanthosis nigricans that may have generalised, hyperkeratotic, ichthyosiform plaques and be inherited in an autosomal-dominant pattern.[2][34]
INVESTIGATIONS
On skin biopsy, ichthyosis hystrix may have a pattern of epidermolytic hyperkeratosis or more non-specific findings of hyperkeratosis, hypergranulosis, acanthosis, and papillomatosis.[33]
Pemphigus
SIGNS / SYMPTOMS
Resolving pemphigus vulgaris or pemphigus foliaceus may have a papillomatous, hyperpigmented appearance, which clinically and histologically resembles acanthosis nigricans.[35][36]
INVESTIGATIONS
Patients with pemphigus have auto-antibodies that can be detected in the blood or by direct immunofluorescence of skin lesions.[36]
Tinea corporis
SIGNS / SYMPTOMS
May clinically resemble acanthosis nigricans, especially if there is post-inflammatory hyperpigmentation.
INVESTIGATIONS
Evidence of dermatophytes on potassium hydroxide (KOH) preparation or Periodic Acid-Schiff (PAS) staining on histology.
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