Chapter 25 The Skin

The Skin: More than a Mechanical Barrier Squamous epithelial cells Melanocytes Dendritic cells Lymphocytes Neural end organs and axonal processes Adnexal components Sweat glands Hair follicles Definitions of Macroscopic Terms Definitions of microscopic Terms

Definition of Macroscopic Terms ExcoriationTraumatic lesion breaking the epidermis and causing a raw linear area( deep scratch): often self-induced LichenificationThickened and rough skin characterized by prominent skin markings: usually the result of repeated rubbing

Definition of Macroscopic terms MaculeCircumscribed lesion, 5mm or smaller in diameter characterized by flatness and distinguished by coloration (patch is greater than 5 mm) OnycholysisSeparation of nail plate from nail bed

Definition of Macroscopic Terms PapuleElevated dome-shaped or flat-topped lesion 5 mm or less across ( nodule is greater than 5mm) PlaqueElevated flat-topped lesion, usually greater than 5mm across ( may be caused by coalescent papules)

Definition of Macroscopic Terms PustuleDiscrete, pus-filled, raised lesion ScaleDry, horny, platelike excrescence: usually the result of imperfect cornification

Definition of Macroscopic Terms VesicleFluid-filled raised lesion 5mm or less across ( Bulla is greater than 5mm. Blister is the common term for both) WhealItchy, transient, elevated lesion with variable blanching and erythema formed as a result of dermal edema

Definition of Microscopic Terms AcantholysisLoss of intercellular cohesion between keratinocytes AcanthosisDiffuse epidermal hyperplasia DyskeratosisAbnormal, premature keratinization within cells below the stratum granulosum

Definition of Microscopic Terms ErosionDiscontinuity of the skin showing incomplete loss of the epidermis ExocytosisInfiltration of the epidermis by inflammatory cells Hydropic swellingIntracellular edema of (Ballooning)keratinocytes, often seen in viral infections

Definition of Microscopic Terms HypergranulosisHyperplasia of the stratum granulosum, often due to intense rubbing HyperkeratosisThickening of the stratum corneum, often associated with a qualitative abnormality of keratin

Definition of Microscopic Terms LentiginousA linear pattern of melanocyte proliferation within the epidermal basal cell layer PapillomatosisSurface elevation caused by hyperplasia and enlargement of contiguous dermal papillae ParakeratosisKeratinization with retained nuclei in the stratum corneum. On mucous membranes parakeratosis is normal.

Definition of Microscopic Terms SpongiosisIntercellular edema of the epidermis UlcerationDiscontinuity of the skin showing complete loss of the epidermis revealing dermis or subcutis VacuolizationFormation of vacuoles within or adjacent to cells; often refers to basal cell- basement membrane zone area

Disorders of Pigmentation and Melanocytes Freckle (Ephelis) Lentigo Melanocytic nevus (pigmented nevus, mole) Junctional nevi -> compound nevi -> intradermal nevi Maturation Dysplastic nevi Precursors of melanoma Melanoma Radial growth ( horizontal ) vs vertical growth Inherited genes and sun exposure ABCs of melanoma Prognostic factors Tumor depth Number of mitoses Tumor regression Tumor infiltrating lymphocytes Gender Location

Benign Epithelial Tumors Seborrheic keratoses Acanthosis nigricans – DM, malignancy Fibroephithelial polyp – skin tag Epithelial cyst (wen) Adnexal (appendage) tumors

Premalignant and Malignant Epidermal Tumors Actinic keratosis Squamous cell carcinoma – nodular, scaley, may ulcerate Basal cell carcinoma – pearly papules, prominent telangiectasias Sun exposure and DNA damage

Tumors of the Dermis Benign fibrous histiocytoma (dermatofibroma) Dermatofibrosarcoma proturberans

Tumors of Cellular Migrants to the Skin Mycosis fungoides (cutaneous T cell lymphoma) Sezary-Lutzner cells Mastocytosis Mast cell degranulation Darier sign, dermatographism

Disorders of Epidermal Maturation Icthyosis Defective desquamation Impaired epidermal maturation

Acute Inflammatory Dermatoses Urticaria – hives Wheal and flare IgE mediated – Type I hypersensitivity Acute eczematous dermatitis Allergic contact dermatitis Atopic dermatitis Drug-related eczematous dermatitis Photoeczematous dermatitis Primary irritant dermatitis Erythema multiforme Infections, drugs, collagen vascular diseases Macules, papaules, vesicle, bullae, target lesions Steven-Johnson syndrome – erosions of skin and mucous membranes, toxic epidermal necrolysis

Chronic Inflammatory Dermatoses Psoriasis Well-demarcated pink to salmon-coored plaques with silver- white scale Arthritis, myopathy, enteropathy, spondylitic joint disease, AIDS Elbows, knees, scalp, lumbosacral areas, intergluteal cleft, glans penis Nail changes Pustular psoriasis HLA-C Seborrheic dermatitis Scalp, forehead, face, presternal area Leiner disease, cradle cap, HIV, Parkinson disease, sebum, yeast Lichen Planus – pruritic, purple, polygonal, planar papules, plaques

Blistering (Bullous) Diseases Inflammatory Blistering Disorders Pemphigus Autoantibodies that result in dissolution of intracellular attachments within the epidermis and mucosal epithelium Acantholysis Bullous pemphigoid Subepidermal, nonacantholytic blisters Linear deposition of immunoglobulin and complement in the basement membrane zone Dermatitis herpetiformis Urticaria and grouped vesicles, celiac disease, symmetric extensor surfaces Noninflammatory Blistering Disorders Epidermolysis Bullosa and Porphyria

Disorders of Epidermal Appendages Acne vulgaris Noninflammatory – open and closed comedones Inflammatory – papules, nodules,pustules Propionibacterium acnes Androgens Rosacea Inappropriate activation of the innate immune system

Panniculitis Erythema nodusum and erythema induratum

Infection Verrucae (warts) - HPV Molluscum contagiosum – pox virus, umbilicated lesions Impetigo – strep and staph, honey-colored crust Superficial fungal infections – tinea capitis, barbae, corporis, cruris, pedis, onychomycosis, dermatophytes; versicolor - yeast