Acanthosis: Histopathology, Causes, and Clinical Correlations

Acanthosis is histologic thickening of the stratum spinosum (prickle cell layer) with elongation of rete ridges. It reflects keratinocyte hyperproliferation or decreased turnover.

Major Etiologic Categories

• Inflammatory Dermatoses: Psoriasis (regular acanthosis), eczema (spongiotic acanthosis), lichen planus (saw-tooth rete ridges).
• Hyperproliferative/Neoplastic: Seborrheic keratosis, actinic keratosis, Bowen's disease (SCC in situ), squamous cell carcinoma.
• Viral Infections: HPV (verruca vulgaris, condyloma), molluscum contagiosum.
• Drug-Induced: EGFR inhibitors, BRAF inhibitors, chemotherapy (e.g., capecitabine — hand-foot syndrome).
• Genetic Disorders: Darier disease (acantholytic dyskeratosis), Hailey-Hailey disease, epidermolytic ichthyosis.
• Endocrine/Metabolic: Acanthosis nigricans (insulin resistance, obesity, malignancy-associated).

Microscopic Features

• Increased spinous cell layers (>5–10)
• Elongated, often anastomosing rete ridges
• Variable: hyperkeratosis, parakeratosis, spongiosis, acantholysis, dyskeratosis, nuclear atypia (context-dependent)

Management

Treat the underlying condition. Topical retinoids, calcipotriene, or keratolytics for benign hyperkeratotic lesions. For acanthosis nigricans: weight loss, insulin sensitizers, malignancy workup if acute/severe onset. Surgical excision for neoplastic lesions.