Dermatology: Skin Conditions

• Dermatology is the study of skin

Scabies

• Presents as a progressive rash with small, red spots
• Typically found on hands, feet, and genitals
• Known for being extremely itchy, often disrupting sleep
• Transmitted from person to person, highlight the importance of checking contacts for similar rashes
• Treated with topical permethrin

Lichen Planus

• Characterized by a pruritic rash with symmetrically distributed pink papules
• The 6 P's mnemonic helps recall key features: Pruritic, Purple, Polygonal, Planar Papules, and Plaques
• Biopsy reveals bandlike infiltration of lymphocytes and saw-tooth rete ridges

Hookworm

• Occurs after walking barefoot in soil or sand, where transmission happens through direct skin contact
• Results in a pruritic maculopapular lesion at the entry site, often on the foot
• Tracks may be visible in the lesion, showing the worm's path

Kaposi Sarcoma

• Typically presents in HIV patients as red, purple, or brown lesions/papules on lower extremities
• Lesions may appear cherry-red and slightly raised
• Caused by HHV-8 (human herpesvirus type 8), which infects endothelial cells, leading to their differentiation and potential transformation into cancer
• Histopathology reveals spindle-shaped endothelial cells, red blood cells in slit-like vascular spaces, and inflammation with lymphocytes and plasma cells

Melanoma

• A malignancy of melanocytes, which originate from neural crest cells
• Immunohistochemistry markers include S-100, HBM-45, and Vimentin
• Can also be associated with the BRAF V600E mutation

Lentigo Maligna

• A subtype of melanoma that occurs on sun-exposed skin in the elderly
• Presents as a 1.5-cm brown-black mottled, scaly lesion with irregular borders
• Biopsy shows atypical melanocytes

Cherry Angioma

• Develops in adults
• Does not spontaneously regress

Strawberry Angioma

• A fast growing red plaque on a child that will spontaneously regress
• Usually occurs on the head or neck
• Composed of proliferating endothelial cells and is a benign vascular tumor

Acne

• Presents as scattered comedones and papules on face
• Follicular epidermal hyperproliferation with excess production of sebum causes acne
• First line treatment includes tretinoin or other retinoids
• Treatment decreases cohesion between epidermal cells and increases epidermal cell turnover

Actinic Keratosis

• Premalignant lesion from increased sun exposure
• Can progress to squamous cell carcinoma

Urticaria

• Hives usually associated with a hypersensitivity disorder
• Often associated with IgE-mediated degranulation of mast cells (type I hypersensitivity)
• Pathophysiology involves the superficial dermis becoming more permeable, causing fluid to build up and resulting in dermal edema

Diaper Dermatitis

• Irritant contact diaper dermatitis presents as erythematous papules in the diaper area while sparing the skin folds
• Skin barrier breakdown from exposure to fecal bacteria increases local skin pH leading to diaper dermatitis
• Treated with barrier ointment to stop the skin from contacting urine and stool

Erythema Multiforme

• Immune mediated rash that starts as erythematous papules but turns into target lesions
• Infectious antigens are deposited into keratinocytes, causing a strong T cell immune response
• Most commonly associated with HSV, but respiratory tract infections due to mycoplasma pneumoniae frequently cause erythema multiforme in children

Tinea

• Round, oval lesions with raised borders; also known as ringworm
• Caused by Trichophyton rubrum (infection of keratinized matter)

Basal Cell Carcinoma

• Skin cancer of the basal cells, the deepest part of the epidermis
• Extensive sun exposure can cause it
• Presents as a round nodule, skin-colored on face
• Biopsy shows nodular aggregates of dark-blue staining (basophilic), basaloid keratinocytes in the dermis with peripheral palisading and cleft formation
• Originates from epidermal keratinocytes
• If left untreated, can cause local growth with progressive tissue destruction
• Rarely metastasizes but may continue to grow, causing destruction of surrounding tissue

Psoriasis

• Presentation: On extensors
• Biopsy: Hyperkeratosis, Epidermal hyperplasia, Neutrophilic foci
• Treated with topical corticosteroids and phototherapy
• Use of Vitamin D in the skin

Head Lice

• Caused by Pediculus humanus capitis
• Treated with topical pediculicides (permethrin, ivermectin)

Blister Disorders

Dermatitis Herpetiformis

• Blistering skin disorder
• Presents as tense, pruritic blisters and history of celiac disease
• Histology shows subepidermal blisters with granular pattern of IgA deposition at the dermal papillae

Bullous Pemphigoid vs Pemphigus Vulgaris

• Both are type two hypersensitivity (antibody driven)
• BP
  • Blisters intact
  • Antibodies to hemidesmosome (deeper, so blisters are still intact)
  • Hemidesmosome attaches epidermal keratinocytes to the extracellular matrix of the dermis at the dermal-epidermal junction
• PV
  • Blisters popped
  • Antibodies to desmosome

Contact Dermatitis

• Hypersensitivity type IV
• Histological examination shows intercellular edema with infiltration of lymphocytes and eosinophils, known as spongiosus
• Accumulation of fluid between keratinocytes in the epidermis marks spongiosis

Tinea Pedis (Athlete's Foot)

• Fungal foot infection
• Presents with erythema and excoriation between the toes
• Treated with topical antifungals (clotrimazole)
• Albendazole is an anthelmintic, not an antifungal

Cells of Epidermis

Langerhans cells

• Dendritic cells (APCs) that look like tennis racquets
• As APCs, they can interact closely with T lymphocytes

Aging

• Wrinkling is caused by decreased collagen fibril production, increased collagen crosslinking, degradation and degradation of elastin

Ecchymosis

• Bruise

Epidermolysis bullosa

• Blister disorder
• Presents with blisters on feet after starting to walk (caused by friction of minor trauma)
• Caused by antibodies against or a mutation of the anchoring fibrils, part of the hemidesmosome
• Any defect in hemidesmosome will result in blisters
• Biopsy shows impaired keratin filament assembly

Pityriasis Rosea

• Self-limiting but progressive and itchy rash
• Presents as an itchy rash that started as one patch then progressed to several
• Presents with “Herald patches” that are oval red patches that are scaly
• Can be in a “christmas tree” formation on back

Waardenburg syndrome

• Abnormal migration of neural crest cells (melanocytes) that cause patchy depigmentation on hair and deafness

Tinea versicolor

• Fungal infection of malassezia furfur
• Presents with hypopigmentation problems