Master Dermatology
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Core Concepts
The skin comprises epidermis, dermis, and subcutis. Functions include protection, thermoregulation, sensation, and vitamin D synthesis. Key dermatologic terms describe primary lesions (e.g., macule, papule, vesicle, pustule, wheal) and secondary lesions (e.g., scale, crust, ulcer, lichenification). Fitzpatrick scale (Type I-VI) classifies skin type for sun response.
Clinical Presentation
- Eczema (Atopic Dermatitis): Pruritic, inflammatory; erythematous papules/vesicles/crusting (acute); lichenification (chronic). Typically flexural.
- Psoriasis: Chronic autoimmune. Well-demarcated, erythematous plaques with silvery scales, extensor surfaces (elbows, knees, scalp). Nail pitting, arthritis possible.
- Acne Vulgaris: Affects pilosebaceous units. Comedones, papules, pustules, nodules, cysts on face, chest, back. Hormonal influence.
- Rosacea: Chronic facial erythema, flushing, telangiectasias, papules, pustules (no comedones). Triggers: heat, alcohol.
- Tinea (Dermatophytosis): Fungal. Pruritic, annular, scaly lesions with central clearing (e.g., Corporis). Also Pedis, Cruris, Capitis, Unguium (nails).
- Candidiasis: Yeast infection. Erythematous, macerated patches with satellite lesions in skin folds (intertrigo), oral thrush, vulvovaginitis.
- Impetigo: Superficial bacterial (S. aureus, Strep). Honey-crusted lesions, usually perioral/nasal.
- Cellulitis: Acute bacterial (S. pyogenes, S. aureus) dermis/subcutis infection. Expanding erythema, warmth, pain, swelling, ill-defined borders. Erysipelas is more superficial, sharply demarcated.
- Herpes Simplex Virus (HSV): Grouped vesicles on an erythematous base (cold sores, genital herpes). Recurrent.
- Varicella Zoster Virus (VZV): Chickenpox: Widespread pruritic vesicles, different stages. Shingles: Unilateral, dermatomal vesicular eruption, severe pain, post-herpetic neuralgia.
- Urticaria (Hives): Transient (<24h/lesion), intensely pruritic, erythematous, raised wheals. Often with angioedema.
- Basal Cell Carcinoma (BCC): Most common skin cancer. Pearly papule/nodule with rolled border, telangiectasias, central ulceration. Rarely metastasizes.
- Squamous Cell Carcinoma (SCC): Second most common. Erythematous, scaly, indurated plaque/nodule, often with crusting/ulceration. Arises from actinic keratosis. Higher metastatic risk.
- Melanoma: Malignant neoplasm of melanocytes. ABCDE (Asymmetry, Border, Color, Diameter >6mm, Evolving). Most aggressive.
Diagnosis (Gold Standard)
Clinical examination and detailed history are paramount. Gold standard for definitive diagnosis includes Biopsy (excisional/incisional/punch) for suspicious lesions or inflammatory dermatoses via histopathology. Other key diagnostic aids are Potassium Hydroxide (KOH) preparation for fungal infections, Dermoscopy for pigmented lesions, Tzanck Smear for herpetic infections, Patch Testing for allergic contact dermatitis, and Bacterial Culture for resistant infections.
Management (First Line)
Initial management emphasizes General care (emollients, sun protection). For Eczema/Psoriasis, topical corticosteroids/calcineurin inhibitors are first line; severe cases require phototherapy or systemic agents. Acne Vulgaris starts with topical retinoids/benzoyl peroxide/antibiotics; oral antibiotics or isotretinoin for moderate/severe. Rosacea responds to topical metronidazole/azelaic acid or oral tetracyclines. Fungal Infections are treated with topical antifungals, oral for extensive/scalp/nails. Bacterial Infections (Impetigo, Cellulitis) require topical mupirocin or oral/IV antibiotics. Herpes Simplex/Zoster benefit from oral antivirals. Urticaria is managed with oral H1 antihistamines. Skin Cancers (BCC, SCC, Melanoma) primarily involve surgical excision, with Mohs for select high-risk cases.
Exam Red Flags
- Rapidly Changing Mole: Especially with ABCDE criteria (Melanoma).
- Non-healing Ulcer/Sore: Especially on sun-exposed skin (BCC, SCC).
- Widespread Blistering/Erosive Rash: Life-threatening (Pemphigus, Pemphigoid, SJS/TEN).
- Erythroderma: >90% body surface erythema, scaling, systemic symptoms.
- Rash with Fever and Systemic Toxicity: Meningococcemia, SJS/TEN, DRESS.
- Cellulitis with Sepsis Symptoms.
- Immunosuppression with Atypical Skin Infections.
- Unexplained Bruises/Burns: Suspect non-accidental injury.
Sample Practice Questions
A 4-month-old infant is brought to the clinic with an intensely pruritic rash, primarily affecting the cheeks, scalp, and extensor surfaces of the arms and legs. The skin appears erythematous, scaly, and there are some excoriations. The mother reports the infant is constantly scratching and is often irritable. There is a family history of asthma and hay fever. What is the cornerstone of management for this condition?
A 28-year-old woman is concerned about a mole on her back that has recently changed in size and color. On examination, the lesion is asymmetric, has irregular borders, varying shades of brown and black, and measures approximately 7mm in diameter. She has fair skin and a history of severe sunburns during childhood. What is the most appropriate next step in the management of this lesion?
A 60-year-old male presents for a routine check-up and points out a new mole on his back that he noticed approximately 4 months ago. On examination, the lesion is asymmetrical with irregular, notched borders. Its color varies, showing shades of dark brown, black, and some areas of pinkish-red. It measures approximately 8mm in diameter and appears to be slightly raised. He denies any pain or itching. What is the most appropriate immediate next step?
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