Acanthosis

Acanthosis is a histopathological pattern defined by thickening of the epidermis due to hyperplasia of the stratum spinosum, the prickle-cell layer of the epidermis. It is a descriptive term for a cellular change and does not specify a single disease. In many cases, acanthosis is accompanied by elongation of the rete pegs and may occur with accompanying hyperkeratosis; the granular layer can be preserved or thickened depending on the underlying condition. Acanthosis can affect skin and mucosal surfaces and is seen as part of various inflammatory, reactive, and neoplastic processes.

Histologically, acanthosis shows an increased number of keratinocytes in the spinous layer, often with an overall thicker and more irregular epidermis. Surface features may include papillomatosis, giving an undulating appearance. The pattern helps distinguish acanthosis from other epidermal changes such as acantholysis, which is a loss of cell-to-cell cohesion.

Clinically, acanthosis is most commonly encountered as part of acanthosis nigricans, a syndrome characterized by velvety, hyperpigmented plaques in folds such as the neck, axillae, or groin. Acanthosis nigricans can be associated with insulin resistance and obesity, diabetes mellitus, endocrine disorders, or, less commonly, internal malignancies (notably gastric adenocarcinoma). However, acanthosis itself can be a feature of many dermatologic conditions, including psoriasis, lichen planus, or chronic irritation.

In diagnosis and management, acanthosis is treated by addressing the underlying cause when possible, while dermatologic care may focus on symptom relief and prevention of irritation. It remains a descriptive term used in pathology to communicate epidermal hyperplasia patterns rather than a disease entity on its own.