Cutaneous Infections and Infestations
Bacterial
Impetigo (nonbullous: S. aureus/group A strep; bullous: S. aureus toxin), cellulitis, erysipelas, and staphylococcal scalded skin syndrome (exfoliative toxin cleaving desmoglein 1) are core. Know when to culture and when empiric therapy suffices.
Viral
Herpes simplex and zoster (dermatomal, Tzanck/PCR), molluscum contagiosum (umbilicated papules, Henderson-Paterson bodies), HPV (verruca, condyloma), and pityriasis versicolor (Malassezia, spaghetti-and-meatballs on KOH).
Fungal
Dermatophytes (tinea capitis, corporis, pedis, onychomycosis), Candida, and deep mycoses. KOH preparation is the first-line bedside test; culture confirms species. Tinea capitis in children usually requires oral therapy (griseofulvin or terbinafine).
Infestations
Scabies (burrows, nocturnal itch, permethrin or ivermectin), pediculosis, and cutaneous larva migrans (serpiginous track, albendazole/ivermectin).
Traps
- Assuming all tinea capitis responds to topical therapy; oral is standard in children.
- Missing scabies because of excoriated papules only; look for burrows and treat contacts.
- Confusing erythema migrans (Lyme) with tinea corporis; central clearing without scale favors Lyme.
Rule of thumb
When a question shows an annular lesion, ask: scale (dermatophyte) vs central clearing without scale (Lyme) vs trailing scale (pityriasis rosea).
Worked example
A child with patchy hair loss and broken hairs: KOH shows spores; treat with oral griseofulvin/terbinafine plus antifungal shampoo.