AOBD Dermatology cheat sheet

Atopic dermatitis: flexural distribution in adults; chronic pruritus, xerosis, and personal/family history of atopy support diagnosis.

Psoriasis plaques are sharply demarcated with silvery scale; Auspitz sign (pinpoint bleeding on scale removal) and Koebner phenomenon are characteristic.

Pemphigus vulgaris: intraepidermal (suprabasal) acantholysis, flaccid bullae, positive Nikolsky sign; direct immunofluorescence shows intercellular IgG (net-like).

Bullous pemphigoid: subepidermal blister, tense bullae, linear IgG and C3 along the basement membrane zone on DIF.

Dermatitis herpetiformis: granular IgA deposits in dermal papillae; associated with gluten-sensitive enteropathy.

Basal cell carcinoma: pearly papule with telangiectasia, rolled border; nodular, superficial, morpheaform subtypes; rarely metastasizes.

Melanoma ABCDE: Asymmetry, Border irregularity, Color variation, Diameter >6 mm, Evolving lesion.

Scabies: burrows in web spaces, nocturnal pruritus; mineral oil scraping shows mites, eggs, or scybala; treat patient and close contacts.

Miliaria crystallina: obstruction of eccrine ducts at stratum corneum; clear superficial vesicles without inflammation.

Miliaria rubra: duct obstruction deeper in epidermis; erythematous papulovesicles, often in skin folds and occluded areas.

Erythema toxicum neonatorum: appears in first days of life, blotchy erythema with pustules containing eosinophils; self-limited.

Transient neonatal pustular melanosis: present at birth, pustules rupture leaving hyperpigmented macules with collarette scale; no treatment needed.

Kawasaki disease: fever ≥5 days plus 4 of 5 criteria (rash, conjunctivitis, oral changes, extremity changes, cervical lymphadenopathy); risk of coronary aneurysms.

Staphylococcal scalded skin syndrome: exfoliative toxin causes superficial epidermal cleavage; Nikolsky positive; treat with antibiotics.

Hemangioma of infancy: appears shortly after birth, proliferates then involutes; complications include ulceration and airway involvement.

Tinea capitis in children: often Trichophyton tonsurans; presents with scaling, alopecia, or kerion; oral antifungal required.

Mohs is indicated for basal cell carcinoma and squamous cell carcinoma in high-risk anatomic sites (face, ears, nose, lips) or with aggressive histology.

Frozen-section Mohs examines 100% of the peripheral and deep margins by mapping and sectioning the excised tissue en face.

Each Mohs stage: excise, map, orient (inks), freeze, section, and examine; repeat until margins are clear.

Indications also include recurrent tumors, large tumors, ill-defined borders, and tumors in cosmetically or functionally sensitive areas.

Contraindications include tumors with extensive subclinical spread or those requiring complex reconstruction beyond Mohs capability.

Mohs may be used for melanoma with appropriate immunohistochemistry (e.g., MART-1) and specialized training.

Tissue mapping uses a grid with marks to correlate the clinical defect with histologic sections.

Mohs is generally not indicated for benign lesions or for tumors where margins are easily assessed and clear with standard excision.

Lichen planus: hyperkeratosis, wedge-shaped hypergranulosis, saw-tooth rete ridges, band-like lymphocytic infiltrate at dermoepidermal junction.

Psoriasis histology: regular acanthosis, thinned suprapapillary plates, parakeratosis, Munro microabscesses (neutrophils in stratum corneum).

Pemphigus: suprabasal acantholysis with tombstoning of basal cells; intercellular IgG on DIF.

Dermatitis herpetiformis: subepidermal blisters with neutrophilic microabscesses in dermal papillae; granular IgA on DIF.

Mycosis fungoides: epidermotropism of atypical lymphocytes, Pautrier microabscesses, cerebriform nuclei.

Seborrheic keratosis: horn cysts, pseudohorn cysts, basaloid cells, and melanin pigment; benign.

Actinic keratosis: atypical keratinocytes in lower epidermis, parakeratosis, solar elastosis in dermis.

Direct immunofluorescence is essential for autoimmune blistering diseases; location and pattern (intercellular vs linear vs granular) guide diagnosis.