Dermatology Review: Skin Structure, Pathology, and Disorders

A complete set of vocabulary flashcards covering skin layers, cellular junctions, histopathology terms, primary/secondary lesions, and major dermatological conditions as presented in the lecture notes.

Epidermis

The outermost layer of the skin derived from the ectoderm.

Dermis

The middle layer of the skin derived from the mesoderm, consisting of the papillary and reticular layers.

Hypodermis

The deepest layer of the skin, also known as the subcutaneous layer, derived from the mesoderm.

Keratinocytes

Structural cells of the epidermis filled with keratin.

Langerhan cells

Antigen presenting immune cells located within the epidermis.

Merkel cells

Neuroendocrine cells found in the epidermis.

Melanocytes

Melanin producing cells located in the stratum basale.

Tight Junctions (zonula occludens)

Cellular connections composed of claudins and occludins that prevent the paracellular movement of ions and metabolites.

Adherens Junctions (zonula adherens)

Connect the actin cytoskeletons of adjacent cells using $Ca^{2+}$ mediated E-cadherin proteins.

Desmosomes (macula adherens)

Structural supports that connect the intermediate filaments of adjacent cells using desmoplakin, desmocollin, and desmoglein.

Hemidesmosomes

Connections between epithelial cells and the basement membrane using integrins, laminin 5, intermediate filaments, and type 4 collagen.

Gap Junctions

Porous channels composed of 6-piece connexon proteins that facilitate electrochemical communication.

Hyperkeratosis

An increased thickness of the stratum corneum, commonly seen in calluses and psoriasis.

Parakeratosis

The retention of nuclei within the stratum corneum, often associated with psoriasis and actinic keratosis.

Hypergranulosis

An increased thickness of the stratum granulosum, seen in conditions like lichen planus.

Spongiosis

The accumulation of fluid within intercellular spaces, characteristic of atopic or allergic contact dermatitis.

Acanthosis

Epidermal hyperplasia specifically of the stratum spinosum, associated with acanthosis nigricans.

Acantholysis

The separation of cells in the epidermis, often involving desmoglein 1 and yielding a positive Nikolsky sign.

Macule

A flat discoloration measuring $\leq 1\,cm$ in diameter.

Patch

A flat discoloration measuring $\geq 1\,cm$ in diameter.

Papule

An elevated skin lesion measuring $\leq 1\,cm$ in diameter.

Plaque

An elevated skin lesion measuring $\geq 1\,cm$ in diameter.

Vesicle

A fluid-filled blister measuring $\leq 1\,cm$ in diameter.

Bulla

A fluid-filled blister measuring $\geq 1\,cm$ in diameter.

Wheal

A transient, edematous, raised pink papule or plaque.

Lichenification

Thickening of the skin with accentuation of skin markings, often due to repeated excoriation.

Superficial Impetigo

A highly contagious pediatric infection characterized by "honey-colored" crusted lesions caused by Staph. aureus or Strep. pyogenes.

Erysipelas

A superficial dermis infection, typically by Strep. pyogenes, presenting with clear demarcation and raised borders.

Cellulitis

A deep dermal and subcutaneous tissue infection with poorly defined borders, often following minor trauma.

Staphylococcal Scalded Skin Syndrome (SSSS)

A diffuse staphylococcal infection where exfoliative toxin cleaves desmoglein 1, leading to stratum granulosum cleavage and a positive Nikolsky sign.

Necrotizing Fasciitis

A surgical emergency involving infection of the fascia, characterized by crepitus and pain out of proportion to exam findings.

Tzanck smear

A diagnostic test for herpes infections that identifies multinucleated giant cells and Cowdry A inclusions.

Herpes Zoster (Shingles)

A secondary infection of VZV that presents in a dermatomal distribution; can involve the nasociliary nerve (Hutchinson sign).

Molluscum Contagiosum

Small painless, pearly, or flesh-colored papules with central umbilication caused by an enveloped DNA pox virus.

Koilocytes

Cells with a perinuclear halo seen in HPV infections (Verrucae).

Hairy Leukoplakia

Irregular white painless plaques on the tongue, often EBV-mediated, that cannot be scraped off.

Tinea Versicolor

A Malassezia fungal infection causing hypopigmented or hyperpigmented macules with a "spaghetti and meatball" appearance on KOH prep.

Sporotrichosis

Known as "rose gardener’s disease," caused by Sporothrix schenckii, presenting with red papules and ascending lymphangitis.

Mucormycosis

An opportunistic infection by Mucor or Rhizopus species causing black eschar and necrosis of the nares and palate.

Pemphigus Vulgaris

A life-threatening autoimmune condition involving antibodies against desmoglein 1 and 3, resulting in flaccid bullae and a positive Nikolsky sign.

Bullous Pemphigoid

An autoimmune condition involving antibodies against hemidesmosomes, resulting in tense bullae and a negative Nikolsky sign.

Dermatitis Herpetiformis

A pruritic condition associated with Celiac disease and IgA deposition in the dermal papillae.

Erythema Multiforme

A reactive skin disease characterized by target lesions with a "dusky" center, often associated with HSV-1 or sulfa drugs.

DRESS Syndrome

Drug Reaction with Eosinophilia and Systemic Symptoms, a delayed hypersensitivity reaction causing fever and a morbilliform rash.

Atopic Dermatitis

An erythematous, pruritic condition often linked to filaggrin mutations and the Th2 response ($IL-4$ and $IL-13$).

Hidradenitis Suppurativa

A chronic condition involving occlusion of apocrine glands, leading to painful draining pustules and sinus tracts in the axilla or groin.

Lichen Planus

A condition characterized by the 6 P’s: Pruritic, Pink/Purple, Planar, Polygonal, Papules, and Plaques, often showing Wickham striae.

Auspitz sign

Pin-point bleeding that occurs when psoriasis scales are scraped off.

Basal Cell Carcinoma (BCC)

The most common skin cancer, characterized by waxy, pearly plaques with telangiectasias and palisading nuclei on biopsy.

Melanoma ABCDEs

A diagnostic mnemonic for melanoma: Asymmetry, Border irregularity, Color variation, Diameter $> 6\,mm$, and Evolution.