Chapter 52: Disorders of Skin Integrity and Function

The comprehensive study of skin integrity and function begins by defining key primary and secondary skin lesions and rashes, such as macules, papules, vesicles, bullae, and pustules. It delves into the physiology and classification of pruritus (itching), noting its neurological transmission via free nerve endings and small myelinated type C nerve fibers, and the involvement of peripheral mediators like histamine, tryptase, and neuropeptides such as substance P. The chapter examines common skin disorders, including the pathogenesis of acne vulgaris, which results from increased sebum production, follicular hyperkeratosis, and the colonization of Propionibacterium acnes. Infectious processes are detailed, covering superficial fungal dermatophytoses (tinea/ringworm) caused by dermatophytes like Microsporum and Trichophyton and serious viral eruptions like Herpes Zoster (shingles), caused by the reactivation of the varicella–zoster virus along specific dermatomes, which can lead to complications like postherpetic neuralgia. Inflammatory conditions are explored, including the papulosquamous disorders such as Psoriasis, characterized by silvery-white plaques due to accelerated epidermal cell turnover, and Pityriasis Rosea, noted for its characteristic "Christmas tree branch" pattern. The chapter also addresses severe, life-threatening bullous drug reactions, including Stevens–Johnson syndrome and Toxic Epidermal Necrolysis (TEN). Crucial attention is given to skin neoplasms, comparing the origins and clinical outcomes of Basal Cell Carcinoma, Squamous Cell Carcinoma, and the highly aggressive Malignant Melanoma, emphasizing early detection through the ABCDE assessment rule. Finally, disruptions to skin integrity are examined, including thermal injuries (burns), classified by depth from superficial to full thickness, and pressure ulcers, categorized into four stages of tissue loss caused by unrelieved pressure and friction.