Chapter 2 of 154% of exam

Dermatologic System

Dermatology items are mostly visual-pattern recognition converted into words: morphology, distribution and timing. The blueprint covers acneiform, papulosquamous, desquamating, infectious, keratotic, pigmentary, vesiculobullous and neoplastic disease, plus skin integrity problems such as burns and pressure injury.

Reading the description

Most skin questions give a lesion type and a distribution, and the diagnosis follows from the combination. Pay attention to a first lesion that precedes the rest, lines of distribution, and sites such as web spaces or flexures. Mucosal involvement is a key severity marker.

Pityriasis rosea

A single herald patch followed by smaller oval lesions along skin cleavage lines in a Christmas tree pattern on the back.

Merck Manual Professional Edition, Pityriasis Rosea

Scabies

Intensely itchy papules and burrows in finger webs, wrists, waistline and genitals, often worse at night and shared by household contacts.

Merck Manual Professional Edition, Scabies

Actinic keratosis

Rough, scaly papules on sun-exposed skin that are premalignant, with a risk of progression to squamous cell carcinoma.

Merck Manual Professional Edition, Actinic Keratoses

Blistering and desquamating disease

Blisters are sorted by where the split occurs and how fragile the roof is. Drug-induced desquamation is an emergency that begins with stopping the culprit drug. The extent of body surface area involvement defines the category.

SJS and TEN

Epidermal detachment below 10% of body surface area is SJS, 10 to 30% is overlap, and above 30% is TEN; the causative drug is stopped immediately.

Merck Manual Professional Edition, Stevens-Johnson Syndrome and Toxic Epidermal Necrolysis

Bullous pemphigoid

Tense bullae in older adults, often preceded by itching, with a negative Nikolsky sign and little mucosal involvement.

Merck Manual Professional Edition, Bullous Pemphigoid

Pemphigus vulgaris

Flaccid bullae and painful oral erosions with a positive Nikolsky sign reflect loss of epidermal cohesion.

Merck Manual Professional Edition, Pemphigus Vulgaris

Infection and treatment choices

Skin infections are grouped by organism class, and the treatment follows the class: scabicides for mites, antifungals for dermatophytes and antibiotics for bacterial cellulitis. Close contacts matter for infestations. Topical steroids relieve itch but do not treat infection.

Treat contacts in scabies

Topical permethrin (or oral ivermectin in some cases) is used, with simultaneous treatment of close contacts to prevent reinfestation.

Merck Manual Professional Edition, Scabies

Dermatophytes

Tinea infections are treated with antifungals, not antibacterials or steroids alone.

Merck Manual Professional Edition, Overview of Dermatophytoses

Impetigo

Superficial bacterial infection with honey-colored crusts is typically treated with topical antibiotics when limited.

Merck Manual Professional Edition, Impetigo and Ecthyma

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