Infectious and Tropical Dermatology
Scope
This domain covers bacterial, viral, fungal, mycobacterial, and parasitic skin infections, with emphasis on endemic Iranian problems such as cutaneous leishmaniasis, anthroponotic leprosy foci, dermatophytosis, and tuberculosis.
Core rules
- Bacterial: impetigo and ecthyma (S. aureus/Streptococcus), erysipelas/cellulitis, erythrasma (Corynebacterium; coral-red Wood's lamp), Lyme disease (Borrelia; erythema migrans).
- Mycobacterial: lupus vulgaris (apple-jelly nodules), scrofuloderma, erythema induratum; leprosy classified by Ridley-Jopling, with Fite stain for paucibacillary disease and nerve involvement; type 1 reaction is delayed hypersensitivity, type 2 is erythema nodosum leprosum.
- Fungal: dermatophytes (KOH, culture), Malassezia (pityriasis versicolor), Sporothrix (lymphocutaneous), chromoblastomycosis (Medlar bodies), mucormycosis in diabetics.
- Viral: HSV (Tzanck smear, PCR), VZV, HPV, molluscum, hand-foot-mouth disease.
- Parasitic: scabies (burrows, mites on dermoscopy), cutaneous larva migrans, and Old World cutaneous leishmaniasis (Leishmania major/tropica; Giemsa-stained amastigotes).
Worked example
A patient from an endemic focus has a chronic painless ulcer with a raised violaceous border and satellite papules. Reasoning: the chronicity, border, and satellites suggest cutaneous leishmaniasis; a slit-skin smear shows amastigotes within macrophages. Intralesional meglumine antimoniate is first-line for localized disease; cryotherapy alone may fail.
Traps
Do not use Ziehl-Neelsen alone for paucibacillary leprosy-request Fite. Type 1 leprosy reaction is a nerve-threatening reversal reaction, not a drug allergy. Tinea incognito after topical steroids can mimic psoriasis.