Clin Med: Common Derm Pathophysiology

Melanocytic Lineage (Melanocytes & Melanin Production)

Pathophysiologic category of lesions driven by the proliferation, migration, or altered pigment production of melanocytes (the pigment-producing cells of the neural crest located in the stratum basale), containing benign nevi, atypical nevi, malignant melanoma subtypes, ephelides, solar lentigines, and congenital dermal melanocytosis.

Benign Melanocytic Nevi

A benign, symmetric proliferation of normal melanocytes that matures structurally over time through junctional, compound, and intradermal stages.

Junctional Nevus

An early stage of benign melanocytic proliferation where nests of melanocytes are confined strictly to the dermoepidermal junction.

Compound Nevus

An intermediate stage of benign melanocytic maturation where melanocytes have migrated to occupy both the dermoepidermal junction and the underlying dermis.

Intradermal Nevus

The most mature stage of benign melanocytic nevi, where melanocytes reside entirely within the dermis, presenting as dome-shaped and often containing terminal hairs.

Atypical (Dysplastic) Nevi

An acquired, atypical proliferation of melanocytes displaying irregular architectural and histologic growth patterns.

Malignant Melanoma

An aggressive malignancy arising from the malignant transformation of melanocytes, characterized by horizontal (radial) and subsequent vertical tissue invasion.

Superficial Spreading Melanoma

The most common melanoma subtype, characterized by a prolonged initial radial (horizontal) growth phase within the epidermis before entering a rapid vertical dermal invasion phase.

Nodular Melanoma

An aggressive melanoma subtype displaying a rapid, primary vertical growth phase into the dermis from onset, skipping a prominent radial phase.

Acral Lentiginous Melanoma

A malignant proliferation of melanocytes specifically localized to the palms, soles, or nail beds.

Lentigo Maligna Melanoma

A melanoma in situ subtype that develops slowly within chronically sun-exposed epidermal fields in older adults.

Freckles (Ephelides)

A localized hypermelanosis characterized by an increase in melanin pigment production by a normal number of melanocytes, triggered by UV radiation.

Solar Lentigines

A localized hyperplasia of melanocytes accompanied by increased melanin production induced by chronic, cumulative ultraviolet radiation.

Congenital Dermal Melanocytosis (Mongolian Spots)

A congenital pigmentary condition caused by the failure of dermal melanocytes to complete their embryonic migration from the neural crest to the epidermal basal layer.

Keratinocyte Lineage (Epidermal-Derived Growths)

Pathophysiologic category of benign, premalignant, or malignant growths originating from the structural keratinocytes of the epidermis, including seborrheic keratosis, actinic keratosis, basal cell carcinoma, squamous cell carcinoma, and keratoacanthoma.

Seborrheic Keratosis (SK)

A benign, clonal overgrowth of epidermal keratinocytes resulting in "stuck-on" hyperkeratotic plaques.

Actinic Keratosis (AK)

A UV-induced premalignant proliferation of atypical, dysplastic keratinocytes strictly confined to the lower layers of the epidermis.

Basal Cell Carcinoma (BCC)

A locally invasive, slow-growing epidermal malignancy arising from the multipotent basal cells of the stratum basale.

Squamous Cell Carcinoma (SCC)

A malignant transformation and proliferation of atypical keratinocytes originating within the stratum spinosum layer of the epidermis.

Intradermal Squamous Cell Carcinoma (Bowen's Disease)

An intraepidermal squamous cell carcinoma where malignant keratinocytes are strictly confined by the basement membrane and have not invaded the dermis.

Keratoacanthoma (KA)

A rapidly growing, highly differentiated variant of squamous cell carcinoma characterized by rapid keratinization and central keratin plug formation.

Vascular Lineage (Endothelial Cells & Capillaries)

Pathophysiologic category of lesions arising from the abnormal proliferation, ectasia, or congenital malformation of dermal blood vessels and capillary endothelial cells, including cherry angiomas, pyogenic granulomas, nevus simplex, port-wine stains, infantile hemangiomas, and Kaposi sarcoma.

Cherry Angioma

A benign, localized overgrowth and ectasia of mature capillaries in the dermis that increases in frequency with advancing age.

Pyogenic Granuloma

A reactive, rapid proliferation of capillary vessels, commonly triggered by minor localized skin trauma.

Nevus Simplex

A congenital, transient capillary ectasia/malformation in the superficial dermis.

Port-Wine Stain (Nevus Flammeus)

A permanent, congenital dermal capillary malformation that darkens, thickens, and ectatically expands over time.

Hemangioma of Infancy

A benign vascular tumor driven by rapid endothelial cell proliferation during the first year of life.

Kaposi Sarcoma

An opportunistic, malignant angioproliferative vascular tumor driven by infection with Human Herpesvirus-8 (HHV-8) in immunocompromised patients.

Connective Tissue Lineage (Dermal & Subcutaneous)

Pathophysiologic category of lesions originating from structural cells of the dermis or subcutaneous soft tissue, including dermatofibromas, lipomas, and acrochordons.

Dermatofibroma

A benign, reactive dermal proliferation of fibroblasts and histocyes, often arising after minor trauma.

Lipoma

A benign, slow-growing soft tissue tumor composed of mature adipocytes (fat cells) residing in the subcutaneous space.

Skin Tags (Acrochordons)

Benign pedunculated polyps consisting of a central fibrovascular core enveloped by normal-appearing hyperplastic epidermis.

Pilosebaceous & Appendiceal Lineage (Hair Follicles & Sebaceous Glands)

Pathophysiologic category targeting skin appendages (follicular infundibular walls, hair follicles, or sebaceous glands), including acne vulgaris, rosacea, perioral dermatitis, and epidermal inclusion cysts.

Acne Vulgaris

A chronic inflammatory disease of the pilosebaceous unit driven by follicular hyperkeratinization (plugging), excess sebum production, colonization by Cutibacterium acnes, and subsequent localized inflammation.

Rosacea

A chronic inflammatory vascular and tissue disorder characterized by capillary reactivity, vasomotor flushing, and pilosebaceous inflammation.

Perioral Dermatitis

An inflammatory facial eruption localized around follicular units, frequently triggered or exacerbated by topical corticosteroid use.

Epidermal Inclusion Cyst

A benign subcutaneous cyst formed by the invagination and sealing of the follicular infundibular epidermis, creating a closed sac filled with laminated keratin.

Hair Cycle & Follicular Dynamics (Alopecia)

Pathophysiologic category of hair loss disorders characterized by alterations in the hair follicle's cycle, immune tolerance, or physical integrity, including alopecia areata, androgenetic alopecia, scarring alopecia, traction alopecia, telogen effluvium, and trichotillomania.

Alopecia Areata

A T-cell-mediated autoimmune attack targeting the hair follicle, prematurely shifting follicles into early shedding phases while preserving the underlying follicle structure.

Androgenetic Alopecia

Androgen-mediated progressive miniaturization of genetically susceptible terminal hair follicles.

Scarring (Cicatricial) Alopecia

Direct inflammatory or physical destruction of the hair follicle, leading to permanent replacement of the follicle with fibrous scar tissue.

Traction Alopecia

Physical, mechanical tension that slowly damages and eventually destroys the hair follicle.

Telogen Effluvium

A temporary physiological shock that prematurely shifts a large percentage of active growing hair follicles (anagen phase) into the resting/shedding phase (telogen phase) simultaneously.

Trichotillomania

Mechanical hair extraction due to psychiatric or impulse control triggers, leaving the underlying follicle intact but broken at varying lengths.

Viral Epidermal Pathologies (Intracellular Epithelial Infections)

Pathophysiologic category of infectious eruptions driven by intracellular viruses that selectively infect and alter epidermal keratinocytes or sensory nerve endings, including herpes simplex, shingles, verruca (warts), and molluscum contagiosum.

Herpes Simplex (HSV I & II)

A DNA virus that infects epithelial cells and establishes lifelong latency within sensory ganglia, periodically reactivating to travel down the sensory axon to produce localized, grouped epithelial vesicles.

Shingles (Herpes Zoster)

Reactivation of latent varicella-zoster virus (VZV) in a sensory ganglion, producing a painful dermatomal vesicular eruption.

Verruca (Warts)

Driven by Human Papillomavirus (HPV), which infects the basal keratinocytes of the epidermis, stimulating excess epidermal keratin production and hyperkeratosis.

Molluscum Contagiosum

An epidermal poxvirus infection that causes benign, localized epidermal hyperplasia, presenting as waxy, umbilicated papules.