Cutaneous Infections and Infestations
Domain 4 tests organism-level reasoning: what the lesion is, which test confirms it, and which treatment plus public-health action follows. Iraq-specific epidemiology such as cutaneous leishmaniasis, tinea capitis and scabies outbreaks matters.
Bacterial and viral
- Impetigo: honey-crusted nonbullous (Staphylococcus/Streptococcus) versus bullous (S. aureus toxin); topical mupirocin or oral cephalexin.
- Ecthyma, erysipelas (sharply demarcated, fever) and cellulitis (ill-defined). Erythrasma fluoresces coral-red and responds to erythromycin.
- Herpes simplex: grouped vesicles on erythema, Tzanck smear or PCR. Varicella-zoster is dermatomal. Human papillomavirus causes warts; molluscum contagiosum shows umbilicated papules.
Fungal and mycobacterial
- KOH microscopy then culture. Tinea capitis needs oral griseofulvin or terbinafine, not topical therapy alone.
- Lupus vulgaris and leprosy: Fite stain and nerve examination; the Ridley-Jopling spectrum guides therapy.
- Cutaneous leishmaniasis: painless ulcer with raised undermined edge; slit-skin smear shows amastigotes; intralesional antimony or cryotherapy depending on lesion.
Parasitic and sexually transmitted
- Scabies: burrows, nocturnal itch, mites or eggs on scraping; permethrin 5% and treat all contacts.
- Syphilis: painless chancre, dark-ground microscopy or PCR, RPR/VDRL confirmed by TPPA; benzathine penicillin.
Worked example
A soldier returning from rural Iraq has a 2 cm painless forearm ulcer with a raised border for 6 weeks. Slit-skin smear shows Leishman-Donovan bodies. Diagnosis: cutaneous leishmaniasis (Leishmania tropica). Reasoning: chronicity, undermined edge and endemic exposure; confirm before systemic therapy.
Traps
Steroid-modified tinea may be KOH-negative on surface scale but is still fungal. Do not treat scabies without treating contacts. Do not rely on serology alone for early syphilis.