Skin infections & infestations flashcards
14 high-yield MRCP Part 1 cards from the Intellect Medicos Dermatology course. Try to answer each question before you open it — then study them properly with spaced repetition, which brings each card back just before you would forget it.
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What is the NICE first-line treatment for localised non-bullous impetigo in a patient who is not systemically unwell?
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Hydrogen peroxide 1% cream.
Why? It is effective for localised disease and avoids antibiotic resistance.
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What is the first-line treatment for tinea capitis caused by Trichophyton tonsurans?
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Oral terbinafine.
Why? Topical antifungals alone do not penetrate the hair shaft enough to cure tinea capitis.
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What is the first-line treatment for pityriasis versicolor?
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Topical ketoconazole 2% shampoo (once daily for 5 days); an imidazole cream (e.g. clotrimazole) for small areas.
Why? Pityriasis versicolor is a Malassezia infection causing hypo- or hyperpigmented scaly patches on the trunk.
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What should be done before starting oral antifungal treatment for a suspected fungal nail infection?
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Confirm the diagnosis — send nail clippings (and subungual scrapings) for microscopy and culture.
Why? Psoriasis, trauma and other conditions mimic onychomycosis, and oral treatment is long with side effects.
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What is the first-line treatment for scabies?
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Permethrin 5% cream to the whole body (including scalp and face), washed off after 8–12 hours and repeated after 7 days.
Why? The second application kills mites that hatch from eggs after the first treatment.
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What is the treatment for crusted (Norwegian) scabies in an immunocompromised patient?
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Combination of oral ivermectin and topical permethrin, with specialist advice.
Why? Crusted scabies carries huge mite numbers in thick crusts, with surprisingly little itch, so it is highly transmissible.
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A 4-year-old with atopic eczema develops clusters of painful, punched-out erosions and vesicles on the face over 24 hours. He is febrile and lethargic. What is the management?
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Same-day admission and IV aciclovir (oral aciclovir only if not systemically unwell).
Why? This is eczema herpeticum (HSV superinfection of eczematous skin), which can be life-threatening.
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Erythrasma, a well-demarcated brown-red rash in the groin or axillae, is caused by ______ and shows coral-red fluorescence under Wood's lamp.
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Corynebacterium minutissimum
Why? Fluorescence is due to bacterial porphyrins. First-line treatment is topical miconazole or fusidic acid; oral clarithromycin or erythromycin for extensive disease.
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What is the first-line antibiotic for erysipelas, and the alternative in penicillin allergy?
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Oral flucloxacillin; clarithromycin if penicillin-allergic.
Why? Erysipelas is a superficial Streptococcus pyogenes infection of the upper dermis and lymphatics, giving a sharply demarcated, raised, shiny red plaque.
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What is the first-line treatment for localised tinea corporis?
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A topical antifungal — terbinafine cream or an imidazole (e.g. clotrimazole) cream.
Why? Oral treatment is reserved for severe or extensive disease, ideally after skin scrapings confirm the diagnosis: oral terbinafine first, with itraconazole or griseofulvin if terbinafine is unsuitable.
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Terbinafine inhibits fungal ______, whereas azole antifungals inhibit lanosterol 14α-demethylase (a fungal cytochrome P450 enzyme); both block ergosterol synthesis.
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squalene epoxidase
Why? Azoles also inhibit human CYP enzymes, so they cause many drug interactions; terbinafine can cause taste disturbance and, rarely, liver injury.
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Terbinafine inhibits fungal squalene epoxidase, whereas azole antifungals inhibit ______; both block ergosterol synthesis.
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lanosterol 14α-demethylase (a fungal cytochrome P450 enzyme)
Why? Azoles also inhibit human CYP enzymes, so they cause many drug interactions; terbinafine can cause taste disturbance and, rarely, liver injury.
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What contraception advice applies to griseofulvin?
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It is teratogenic and an enzyme inducer: women need effective contraception during and for 1 month after treatment (the pill may fail); men should not father a child during and for 6 months after.
Why? Griseofulvin is mainly used for Microsporum tinea capitis. As a hepatic enzyme inducer it also reduces the effect of warfarin.
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Which oral antifungal should be avoided in patients with heart failure?
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Itraconazole (negative inotropic effect).
Why? It is also a potent CYP3A4 inhibitor (e.g. avoid with simvastatin) and can cause hepatotoxicity.