USMLE (Fach) / Dermatology (Lektion)
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USMLE First Aid
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- Impetigo - Very superficial skin infection.- Usually form S aureus or S pyogenes.- Highly contagious. - Honey-colored crusting. - Bullous impetigo has bullae and is usually caused by S aureus.
- Erysipelas Infection involving upper dermis and superficial lymphatics, usually from S pyogenes. - Presents with well-defined, raised demarcation between infected and normal skin.
- Cellulitis Acute, painful, spreading infection of deeper dermis and subcutaneous tissues. - Usually from S pyogenes or S aureus. - Often starts with a break in skin from trauma or another infection.
- Necrotizing fasciitis Deeper tissue injury, usually from anaerobic bacteria or S pyogenes. - Pain may be out of proportion to exam findings. - Results in crepitus from methane and CO2 production. - Causes bullae and purple ...
- Staphylococcal scalded skin syndrome Exotoxin destroys keratinocyte attachments in stratum granulosum only (vs toxic epidermal necrolysis, which destroys epidermal-dermal junction). - Characterized by fever and generalized erythematous ...
- Herpes Herpes virus infections (HSV1 and HSV2) of skin. May be found anywhere on the body but are most comon in the perioral and genital areas:- Herpes labialis- Herpes genitalis- Herpetic whitlow (finger) - ...
- Molluscum contagiosum Firm, flesh-colored papules on the skin and mucous membranes. - The papules are often pruritic and have umbilicated centers containing white, curd-like material.- Caused by a poxvirus and is transmitted ...
- Varicella zoster virus Causes varicella (chickenpox) and zoster (shingles). - Presents with multiple crops of lesions in various stages from vesicles to crusts. - Zoster is a reactivation of the virus in dermatomal distribution ...
- Hairy leukoplakia Irregular, white, painless plaques on lateral tongue that cannot be scraped off. - EBV mediated. - Occurs in HIV-positive patients, organ transplant recipients. - Contrast with thrush (scrapable) and ...
- Basal cell carcinoma Most common skin cancer. Found in sun-exposed areas of body (eg, face). - Locally invasive, but rarely metastasizes. - Waxy, pink, pearly nodules, commonly with telangiectasias, rolled borders, central ...
- Verrucae Warts; caused by low-risk HPV (16, 18) strains. - Soft, tan-colored, cauliflower-like papules. - Biopsy is characterized by undulating epidermal hyperplasia with enlarged nuclei and cytoplasmic vacuolization ...
- Skin layers Skin has 3 layers: epidermis, dermis, subcutaneous fat (hypodermis, subcutis). - Stratum corneum (keratin)- Stratum lucidum (most prominent in palms and soles)- Stratum granulosum- Stratum spinosum (desmosomes)- ...
- Epithelial cell junctions Tight junction (zonula occludens) – prevents paracellular movement of solutes; composed of claudins and occludins. Adherens junction (belt desmosome, zonula adherens) – below tight junction, forms ...
- Dermatologic microscopic terms Hyperkeratosis: ↑ thickness of stratum corneum- Examples: Psoriasis, calluses Parakeratosis: Retention of nuclei in stratum corneum- Examples: Psoriasis Hypergranulosis: ↑ thickness of stratum granulosum- ...
- Albinism Normal melanocyte number with ↓ melanin production due to ↓ tyrosinase activity or defective tyrosine transport. - ↑ risk of skin cancer.
- Melasma (chloasma) Hyperpigmentation associated with pregnancy ("mask of pregnancy") or OCP use.
- Vitiligo Irregular patches of complete depigmentation. Caused by autoimmune destruction of melanocytes.
- Seborrheic dermatitis Erythematous, well-demarcated plaques with greasy yellow scales in areas rich in sebaceous glands, such as scalp, face, and periocular region. - Common in both infants and adults, associated with Parkinson ...
- Acne Multifactorial etiology – ↑ sebum/androgen production, abnormal keratinocyte desquamation, Cutibacterium (formerly Propionibacterium) acnes colonization of the pilosebaceous unit (comedones), ...
- Atopic dermatitis (eczema) Pruritic eruption, commonly on skin flexures. - Associated with other atopic diseases (asthma, allergic rhinitis, food allergies); ↑ serum IgE. - Mutations in filaggrin gene predispose (via skin barrier ...
- Allergic contact dermatitis Type IV hypersensitivity reaction that follows exposure to allergen. - Lesions occur at site of contact (eg, nickel, poison ivy, neomycin).
- Melanocytic nevus Common mole. - Benign, but melanoma can arise in congenital or atypical moles. - Intradermal nevi are papular. They are considered to be older lesions in which the epidermal nests of nevus cells have ...
- Pseudofolliculitis barbae Foreign body inflammatory facial skin disorder characterized by firm, hyperpigmented papules and pustules that are painful and pruritic. - Located on cheeks, jawline, and neck. Commonly occurs as a result ...
- Psoriasis Papules and plaques with silver scaling, especially on knees and elbows. - Acanthosis (hyperplasia of stratum spinosum) with parakeratotic scaling (nuclei still in stratum corneum), Munro microabscesses.- ↑ ...
- Rosacea Inflammatory facial skin disorder characterized by erythematous papules and pustules, but no comedones. - May be associated with facial flushing in response to external stimuli (eg, alcohol, heat). ...
- Seborrheic keratosis Flat, greasy, pigmented squamous epithelial proliferation with keratin-filled cysts (horn cysts). Looks "stuck on." - Lesions occur on head, trunk, and extremities.- Common benign neoplasm of older persons. ...
- Urticaria Hives. Pruritic wheals that form after mast cell degranulation. - Characterized by superficial dermal edema and lymphatic channel dilation.
- Angiosarcoma Rare blood vessel malignancy typically occuring in the head, neck, and breast areas. - Usually in elderly, on sun-exposed areas. - Associated with radiation therapy and chronic postmastectomy lymphedema. ...
- Bacillary angiomatosis Benign capillary skin papules found in AIDS patients. - Caused by Bartonella infections. - Frequently mistaken for Kaposi sarcoma, but has neutrophilic infiltrate.
- Cherry hemangioma Benign capillary hemangioma of the elderly. - Does not regress. - Frequency ↑ with age.
- Cystic hygroma Cavernous lymphangioma of the neck. - Associated with Turner syndrome.
- Glomus tumor Benign, painful, red-blue tumor, commonly under fingernails. - Arises from modified smooth muscle cells of the thermoregulatory glomus body.
- Kaposi sarcoma Endothelial malignancy most commonly of the skin, but also mouth, GI tract, and respiratory tract. - Associated with HHV-8 and HIV. - Rarely mistaken for bacillary angiomatosis, but has lymphocytic infiltrate. ...
- Pyogenic granuloma Polypoid lobulated capillary hemangioma that can ulcerate and bleed. - Associated with trauma and pregnancy.
- Strawberry hemangioma Benign capillary hemangioma of infancy (vs cherry hemangioma in elderly). - Appears in first few weeks of life (1/200 births).- Grows rapidly and regresses spontaneously by 5-8 years old.
- Pemphigus vulgaris Potentially fatal autoimmune skin disorder with IgG antibody against desmoglein (component of desmosomes, which connects keratinocytes in the stratum spinosum).- Type II hypersensitivity reaction. - Oral ...
- Bullous pemphigoid Involves IgG antibody against hemidesmosomes (epidermal basement membrane).- Less severe than pemphigus vulgaris.- Type II hypersensitivity reaction. - Tense blisters containing eosinophils affect skin ...
- Dermatitis herpetiformis Pruritic papules, vesicles, and bullae (often found on elbows). - Deposits of IgA at tips of dermal papillae. - Associated with celiac disease. Treatment: dapsone, gluten-free diet.
- Erythema multiforme Associated with infections (eg, Mycoplasma pneumoniae, HSV), drugs (eg, sulfa drugs, β-lactams, phenytoin), cancers, autoimmune disease. - Presents with multiple types of lesions – macules, papules, ...
- Stevens-Johnson syndrome Characterized by fever, bullae formation and necrosis, sloughing of skin at dermal-epidermal junction, high mortality rate. - Typically 2 mucous membranes are involved, and targetoid skin lesions may ...
- Acanthosis nigricans Epidermal hyperplasia causing symmetric, hyperpigmented thickening of skin, especially in axilla or on neck. - Associated with insulin resistance (eg, diabetes, obesity, Cushing syndrome), visceral malignancy ...
- Actinic keratosis Premalignant lesions caused by sun exposure. - Small, rough, erythematous or brownish papules or plaques. - Risk of squamous cell carcinoma is proportional to degree of epithelial dysplasia.
- Erythema nodosum Painful, raised inflammatory lesions of subcutaneous fat (panniculitis), usually on anterior shins. - Often idiopathic, but can be associated with sarcoidosis, coccidioidomycosis, histoplasmosis, TB, ...
- Lichen planus Pruritic, purple, polygonal planar papules and plaques. - Mucosal involvement manifests as Wickham striae (reticular white lines) and hypergranulosis.- Sawtooth infiltrate of lymphocytes at dermal-epidermal ...
- Pityriasis rosea "Herald patch" followed days later by other scaly erythematous plaques, often in a "Christmas tree" distribution on trunk. - Multiple pink plaques with collarette scale. - Self-resolving in 6-8 weeks.
- Sunburn Acute cutaneous inflammatory reaction due to excessive UV irradiation. - Causes DNA mutations, inducing apoptosis of keratinocytes. - UVB is dominant in sunburn.- UVA is dominant in tanning and aging. ...
- Burn classifications First-degree burn: Superficial, through epidermis (eg, common sunburn).- Painful, erythematous, blanching Second-degree burn: Partial-thickness burn through epidermis and dermis. Skin is blistered and ...
- Squamous cell carcinoma Second most common skin cancer. - Associated with excessive exposure to sunlight, immunosuppression, chronically draining sinuses, and occasionally arsenic exposure. - Commonly appears on face, lower ...
- Melanoma Common tumor with significant risk of metastasis. S-100 tumor marker.- Associated with sunlight exposure and dysplastic nevi. Fair-skinned persons are at ↑ risk.- Often driven by activating mutation ...
- Abscess Collection of pus from a walled-off infection within deeper layers of skin. Offending organism is almost always S aureus.