Infectious DiseasesTier 1Disease (DEADMAN)

Common skin infections - fungal infections

Description

Dermatophyte infections ("tinea") - named by site (pedis foot, cruris groin, corporis body, capitis scalp, unguium nail)
Candidal infections - intertrigo, thrush, paronychia - moist skin fold sites, opportunistic
Pityriasis (tinea) versicolor - Malassezia yeast, not a true dermatophyte

Extremely common; tinea pedis prevalence up to ~15-25% of adults
Risk factors: warm/humid climate, occlusive footwear, communal showers/pools, immunosuppression, diabetes, obesity (skin folds)
Tinea capitis predominantly a paediatric disease

Dermatophytes

Trichophyton, Microsporum, Epidermophyton species - keratinophilic fungi confined to stratum corneum, hair, nails
Transmission - person-to-person, fomites (shared towels/footwear), animal contact (zoophilic species, e.g. Microsporum canis from pets - more inflammatory reaction)

Candida

Candida albicans - opportunistic overgrowth in warm, moist, occluded skin (intertrigo), or mucosal surfaces (oral/vaginal thrush); risk factors - diabetes, antibiotic use, immunosuppression, obesity

Pityriasis versicolor

Malassezia (normal skin commensal) - overgrowth related to heat, humidity, sebum, immunosuppression

Clinical

Tinea: annular, scaly, advancing raised border with central clearing, variably pruritic
Tinea pedis: interdigital maceration/scaling, or moccasin-distribution dry scaling
Tinea unguium (onychomycosis): thickened, discoloured, friable nail - confirm before prolonged systemic treatment given differential (psoriasis, trauma)
Candidal intertrigo: beefy red, macerated skin fold with satellite lesions - distinguishes from tinea
Pityriasis versicolor: hypo- or hyperpigmented, finely scaly macules, trunk/upper arms, more visible with tanning

Confirmatory testing (when diagnosis uncertain or before prolonged systemic therapy)

Skin scraping for microscopy (KOH prep) and fungal culture - especially before starting oral antifungals for onychomycosis or tinea capitis
Wood's lamp - some Microsporum species fluoresce (limited sensitivity, not all species fluoresce)

A. Tinea (corporis/cruris/pedis) - localised disease

Topical antifungal (terbinafine cream, or an azole such as clotrimazole) for 1-4 weeks - terbinafine cream has a shorter effective course than azoles for dermatophyte infection
Keep the area dry, treat footwear/hygiene factors (tinea pedis)

B. Extensive, recalcitrant, or specific-site disease requiring oral therapy

Tinea capitis: always requires oral therapy (topical alone inadequate for hair follicle involvement) - oral terbinafine or griseofulvin, choice partly organism-dependent (griseofulvin often preferred for Microsporum species)
Tinea unguium (onychomycosis): oral terbinafine first-line (higher cure rate than azoles for dermatophyte nail disease) for 6 weeks (fingernails) to 12 weeks (toenails); confirm mycology before starting given treatment duration and hepatic monitoring requirement
Extensive tinea corporis/cruris/pedis unresponsive to topical therapy: oral terbinafine or itraconazole

C. Candidal infections

Intertrigo: topical azole (e.g. clotrimazole) +/- low-potency topical steroid combination for inflammation, keep area dry, address predisposing factors (glycaemic control, weight)
Oral/vaginal thrush: topical/oral azole (fluconazole single dose for vaginal candidiasis, nystatin/miconazole oral gel for oral thrush)

D. Pityriasis versicolor

Topical antifungal (selenium sulfide shampoo, or an azole); oral itraconazole/fluconazole for extensive/recurrent disease
Counsel that pigment change can take months to normalise after fungal clearance

Diabetes, obesity, immunosuppression
Hyperhidrosis, occlusive footwear
Onychomycosis - associated with tinea pedis (often coexist, same organism), peripheral vascular disease
HIV - more extensive/atypical fungal skin disease with advancing immunosuppression

Localised tinea - responds well to topical therapy over weeks; recurrence common without addressing moisture/hygiene factors
Onychomycosis - slow response, relapse common, cosmetically and functionally significant (nail thickening can impair footwear fit, contributes to secondary bacterial infection in diabetics)
Untreated tinea pedis - portal of entry for bacterial cellulitis of the lower limb (important secondary prevention link)
Tinea capitis untreated - can progress to kerion (inflammatory boggy mass) with scarring alopecia risk

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