Nevus verrucosus vs. Acanthosis nigricans

Differential Diagnosis

Nevus verrucosus Acanthosis nigricans 1. Orthokeratosis compact 1. Orthokeratosis in basket-woven and lamellate patterns 2. Thick epidermis, either papillated or digitated 2. Thin epidermis 3. Hypergranulosis usually 3. Granular zone normal or slightly decreased in thickness 4. Epidermis sometimes hyperpigmented 4. Epidermis consistently hyperpigmented 5. Projections of elongate dermal papillae above the skin surface, but papillomatosis not prominent 5. Papillomatosis prominent

Discussion

Nevus verrucosus and acanthosis nigricans are processes that affect the papillary dermis and the epidermis. Both conditions may display hyperkeratosis, epidermal hyperpigmentation, papillomatosis, melanophages, and an increased number of fibrocytes in a thickened pale-staining papillary dermis. Whereas nevus verrucosus is fundamentally an epidermal nevus with a rough surface, acanthosis nigricans is basically a connective tissue nevus with a smooth surface.

Nevus verrucosus is but one of many epidermal nevi. It usually is present at birth or appears shortly afterward in the form of tan to brown, rough-surfaced, warty lesions. Like most other epidermal nevi of this type, nevus verrucosus usually is distributed in a circumscribed or systematized fashion, e.g., in linear or zosteriform pattern, and occasionally is widespread, e.g., on one half of the body, it following the lines of Blaschko. Nevus unius lateris is a generic term for all epidermal (and some connective tissue) nevi confined to one side of the body. Rarely, nevus verrucosus may be universal, i.e., the entire integument is covered by it. The attributes of nevus verrucosus in general also apply to other types of epidermal nevi, such as those characterized histopathologically by epidermolytic hyperkeratosis (traditionally known as bullous congenital ichthyosiform erythroderma when widespread and as ichthyosis hystrix when more limited), focal acantholytic dyskeratosis (which is like Darier's disease histopathologically, but not clinically or biologically), cornoid lamellation (which usually is taken to be a histopathologic sign of porokeratosis), and seborrheic keratosis-like (which resembles a seborrheic keratosis histopathologically).

In contrast, acanthosis nigricans may be congenital or acquired. Clinically, irrespective of onset, the lesions are smooth rather than rough-surfaced because the stratum corneum is normal, and histopathologically they are papillomatoses, i.e., exaggerations of dermal papillae, rather than essentially keratoses. The velvety, tan to gray-brown excrescences of acanthosis nigricans tend to develop especially in intertriginous regions, such as the axillae and groin; the neck, umbilicus, and nipples are other sites favored. Conventionally, acanthosis nigricans has been classified into three types as follows: an autosomal dominant anomaly that appears in childhood ("benign" acanthosis nigricans); an aspect of an underlying endocrinologic abnormality, such as acromegaly, gigantism, diabetes insipidus, and Cushing's disease, or from obesity and ingestion of medications, such as corticosteroids and nicotinic acid ("pseudo"-acanthosis nigricans), and a portentous manifestation of an occult malignant neoplasm, usually an adenocarcinoma of the gastrointestinal or genital tract, breast, or lung ("malignant" acanthosis nigricans). Each of these forms of acanthosis nigricans, irrespective of the underlying cause, has the same fundamental clinical and histopathologic attributes.

The terms "benign," "pseudo," and "malignant" in the context of acanthosis nigricans are flawed egregiously and irreparably. Morphologically (clinically and histopathologically) and biologically, acanthosis nigricans is a single process pathologic in the skin. It is neither benign nor malignant (because it is not a neoplasm) and it is authentic, not pseudo. The factors responsible for it, however, are various. Obesity, in itself, is probably not one of them; the endocrinologic factors responsible for obesity probably are. In short, the accurate histopathologic diagnosis is "acanthosis nigricans," unmodified, and that diagnosis should prompt a clinician to consider and seek causes for it.

Other systematized congenital anomalies have aspects clinical and histopathologic reminiscent of acanthosis nigricans, some with such marked papillomatosis that they resemble innumerable fibro-epithelial polyps or papillomas (skin-"tags," acrochordons). They are aberrations of the papillary dermis, i.e., connective tissue nevi. The confluent and reticulated papillomatosis of Gougerot and Carteaud resembles acanthosis nigricans closely histopathologically; whether or not it is a mere manifestation of acanthosis nigricans has yet to be resolved.

In conclusion, the rough surface of nevus verrucosus signifies that it is basically an epidermal process, whereas the smooth surface of acanthosis nigricans indicates that it is primarily a dermal one.

Ref:

Differential Diagnosis In Dermatopathology I, Ii, Iii, Iv.chm