Dermatology Syllabus

Describe the classic morphology of lichen planus (the 6 P's).

Pruritic, Purple (violaceous), Polygonal, Planar (flat-topped), Papules and Plaques; often with white lacy Wickham striae.

What are the three types of atopic dermatitis by age distribution?

Infantile (face/scalp/extensors), childhood (flexural creases), and adult (flexural, hands, lichenified) phases; part of the atopic triad with asthma and allergic rhinitis.

What is the target antigen and immunofluorescence pattern in pemphigus vulgaris?

Autoantibodies against desmoglein 3 (and 1); direct immunofluorescence shows intercellular ('chicken-wire' / fishnet) IgG deposition in the epidermis with suprabasal acantholysis.

Contrast the blister level in bullous pemphigoid versus pemphigus vulgaris.

Bullous pemphigoid is subepidermal (antibodies to BP180/BP230 hemidesmosomes) causing tense bullae; pemphigus vulgaris is intraepidermal (suprabasal, anti-desmoglein) causing flaccid bullae.

What is the target antigen in dermatitis herpetiformis and its associated systemic disease?

IgA against epidermal transglutaminase (tissue transglutaminase); associated with celiac disease (gluten-sensitive enteropathy); DIF shows granular IgA in dermal papillae.

Which autoantibodies are associated with the malar (butterfly) rash of systemic lupus erythematosus?

ANA (sensitive), with anti-dsDNA and anti-Smith being highly specific; skin biopsy shows interface dermatitis and a positive lupus band test on DIF.

What is the inheritance and defective protein in epidermolysis bullosa simplex?

Usually autosomal dominant, caused by mutations in keratin 5 and keratin 14, leading to intraepidermal (basal keratinocyte) blistering.

Which gene is defective in ichthyosis vulgaris?

The filaggrin gene (FLG); loss of filaggrin causes retention hyperkeratosis with fine white scales, and predisposes to atopic dermatitis.

Describe the inheritance and features of neurofibromatosis type 1.

Autosomal dominant, NF1 gene (neurofibromin) on chromosome 17; café-au-lait macules, axillary/inguinal freckling (Crowe sign), neurofibromas, and Lisch nodules.

State the ABCDE criteria for melanoma.

Asymmetry, Border irregularity, Color variegation, Diameter $>6\,\text{mm}$, and Evolution (change over time).

What is the single most important prognostic factor for cutaneous melanoma?

Breslow thickness (depth of tumor invasion in millimeters measured from the granular layer); deeper tumors have worse prognosis.

Contrast basal cell carcinoma and squamous cell carcinoma in terms of metastatic potential.

BCC is the most common skin cancer but rarely metastasizes (locally invasive, 'rodent ulcer' with pearly rolled borders and telangiectasias); SCC can metastasize, especially on lips/ears or in immunosuppressed patients.

What premalignant lesion is a precursor to squamous cell carcinoma?

Actinic (solar) keratosis — rough, scaly erythematous macules/papules on sun-exposed skin.

Which cancer is classically associated with immunosuppression and HHV-8?

Kaposi sarcoma (human herpesvirus 8 / KSHV), presenting as violaceous patches, plaques, and nodules; common in AIDS.

Rank topical corticosteroid potency and give an example of the highest class.

Ranked class I (superpotent, e.g., clobetasol propionate 0.05%) to class VII (least potent, e.g., hydrocortisone 1%/2.5%); higher potency risks atrophy, striae, and telangiectasia.

What is the mechanism of topical calcineurin inhibitors and name two agents?

They inhibit calcineurin, blocking T-cell activation and cytokine production; tacrolimus and pimecrolimus — steroid-sparing agents for atopic dermatitis, safe on face/intertriginous areas.

How much topical medication is one 'fingertip unit' and roughly what area does it cover?

One fingertip unit is about $0.5\,\text{g}$ (the amount from a 5 mm nozzle over the distal fingertip crease) and covers approximately two adult palm areas (~2% BSA).

What is the mechanism of action of topical retinoids in acne?

Retinoids (e.g., tretinoin, adapalene) bind retinoic acid receptors, normalize follicular keratinization, are comedolytic, and reduce inflammation.

What are the key monitoring parameters and teratogenicity risk for isotretinoin?

Monitor lipids and liver transaminases (LFTs); it is highly teratogenic (pregnancy category X), requiring two forms of contraception and pregnancy testing (iPLEDGE).

Name the class and dermatologic uses of methotrexate.

An antimetabolite (dihydrofolate reductase inhibitor) used for severe psoriasis and psoriatic arthritis; requires folic acid supplementation and monitoring of CBC and LFTs due to hepatotoxicity and myelosuppression.

Which biologic targets are used in moderate-to-severe psoriasis? Give the cytokine classes.

TNF-α inhibitors (adalimumab, etanercept), IL-12/23 (ustekinumab), IL-17 (secukinumab, ixekizumab), and IL-23 (guselkumab, risankizumab).

What is the mechanism and main use of oral terbinafine?

An allylantifungal that inhibits squalene epoxidase, blocking ergosterol synthesis; first-line for onychomycosis and tinea capitis; monitor LFTs.

What is phototherapy with narrowband UVB, and its typical wavelength?

A physical therapy using UVB near $311\text{--}313\,\text{nm}$ that suppresses cutaneous immune activity; used for psoriasis, vitiligo, and atopic dermatitis.

What is PUVA therapy?

Psoralen (a photosensitizer) plus UVA ($320\text{--}400\,\text{nm}$) phototherapy; effective for psoriasis and cutaneous T-cell lymphoma but carries increased long-term skin cancer risk.

What is Mohs micrographic surgery and its main advantage?

A staged excision with complete margin evaluation (100% peripheral and deep margin) via frozen sections; offers the highest cure rate with maximal tissue conservation for BCC/SCC in cosmetically sensitive areas.

What is the classic presentation and cause of erythema toxicum neonatorum?

A benign, self-limited eruption of erythematous macules with central pustules/papules in the first days of life; idiopathic, resolves without treatment, and shows eosinophils on smear.

Describe infantile hemangiomas and their natural course.

Benign vascular tumors that appear in the first weeks of life, undergo a rapid proliferative phase then slow involution over years; propranolol is first-line when treatment is indicated.

Which skin changes characterize chronic photoaging in geriatric dermatology?

Solar elastosis, deep wrinkling, dyspigmentation (solar lentigines), telangiectasias, and increased fragility with easy bruising (senile/actinic purpura) from dermal atrophy.

What is the mechanism of botulinum toxin type A in cosmetic dermatology?

It cleaves SNAP-25, inhibiting acetylcholine release at the neuromuscular junction, causing temporary muscle relaxation that softens dynamic rhytides (wrinkles).

What is a chemical peel and how are depths classified?

Application of a caustic agent to induce controlled exfoliation; superficial (e.g., glycolic/salicylic acid, to papillary dermis), medium (e.g., trichloroacetic acid ~35%, to upper reticular dermis), and deep (e.g., phenol, to mid-reticular dermis).

What histologic feature defines spongiosis and which lesions show it?

Spongiosis is intercellular (intraepidermal) edema widening keratinocyte spaces, characteristic of acute eczematous/spongiotic dermatitis; and what is teledermatology's main modality? Store-and-forward transmission of clinical images and history for asynchronous remote diagnosis (versus live interactive video).