Board Review: Papulosquamous Dermatoses

Overview / Definition Papulosquamous dermatoses refer to a category of skin diseases that present with papules and scales. This group includes several distinct conditions, each with unique etiologies, clinical features, and treatment strategies. The recognition of these conditions is crucial for dermatologists as management can vary significantly. Epidemiology The prevalence of papulosquamous dermatoses varies among different conditions: Psoriasis: Affects approximately 2-3% of the population worldwide. Lichen Planus: Estimated incidence of 0.5-2% in the general population. Seborrheic Dermatitis: Common in both infants (cradle cap) and adults, affecting roughly 1-3% of the population. Pathophysiology / Mechanism The pathophysiology of papulosquamous dermatoses varies by condition, but generally involves a combination of genetic, environmental, and immune-mediated factors: Psoriasis: Characterized by hyperproliferation of keratinocytes and an inflammatory infiltrate, particularly involving T cells. Lichen Planus: Thought to be a type IV hypersensitivity reaction, involving lymphocytic infiltration and damage to the basal layer of the epidermis. Seborrheic Dermatitis: Associated with Malassezia yeast, leading to an inflammatory reaction in seborrheic areas. Clinical Presentation Each condition within the papulosquamous dermatoses presents with distinct clinical features: Psoriasis: Red, well-defined plaques covered with silvery scales, often located on elbows, knees, and scalp. Nail changes (pitting, onycholysis) and arthritis may also be present. Lichen Planus: Pruritic, polygonal, flat-topped papules, often on wrists, ankles, and mucous membranes. Wickham's striae (white lines) may be observed. Seborrheic Dermatitis: Erythematous patches with greasy yellow scales, typically found on the scalp, face, and chest. Diagnosis / Workup Diagnosis of papulosquamous dermatoses often relies on clinical examination, but may require additional workup: Clinical Diagnosis: Most co