DermatologyTier 1Disease (DEADMAN)

Fungal infections of skin and nails

Description

Dermatophyte infections (tinea): named by site - tinea pedis (feet), cruris (groin), corporis (body), capitis (scalp), unguium (nails/onychomycosis)
Candidal infections: intertrigo, angular cheilitis, vulvovaginal/balanitis, chronic paronychia
Pityriasis (tinea) versicolor: Malassezia - hypo/hyperpigmented scaly macules, trunk

Tinea pedis very common (public showers, occlusive footwear); tinea capitis mainly paediatric
Onychomycosis prevalence rises with age, diabetes, peripheral vascular disease
Pityriasis versicolor - young adults, worsens in heat/humidity

Dermatophytes (Trichophyton, Microsporum, Epidermophyton) - keratinophilic, invade stratum corneum/hair/nail keratin only
Candida albicans - opportunistic in moist occluded skin folds, diabetes, immunosuppression, antibiotic use
*Malassezia furfur* - commensal yeast, overgrowth in sebum-rich areas -> altered melanocyte pigment production

Clinical - annular, scaly, central clearing with active advancing border (tinea corporis); interdigital maceration/scaling (tinea pedis); thickened, discoloured, friable nails (onychomycosis)
Skin scraping/nail clipping for microscopy (KOH prep) and culture - confirms diagnosis before committing to prolonged oral antifungal therapy, especially for onychomycosis
Wood's lamp - some Microsporum species fluoresce; pityriasis versicolor shows yellow-gold fluorescence

Localised tinea (skin): topical antifungal (terbinafine, clotrimazole) 2-4 weeks
Onychomycosis: oral terbinafine first-line if confirmed on microscopy/culture - 6 weeks (fingernails) to 12 weeks (toenails); baseline and monitoring LFTs given hepatotoxicity risk; topical therapy (amorolfine) for mild/distal disease or where oral therapy contraindicated
Tinea capitis: requires oral therapy (topical alone inadequate - griseofulvin or terbinafine depending on organism)
Candidal intertrigo: topical antifungal + keep area dry, address predisposing factors (diabetes control, weight loss)
Pityriasis versicolor: topical selenium sulfide/azole; oral itraconazole for extensive/recurrent disease

Diabetes, obesity, immunosuppression, peripheral vascular disease predispose to more extensive/recurrent infection
Tinea pedis is a common portal of entry for recurrent bacterial cellulitis
Onychomycosis can be a source of ongoing dermatophyte reservoir/reinfection

Superficial tinea responds well to topical therapy within weeks; untreated spreads and can become chronic
Onychomycosis has high relapse rates even after apparently successful oral therapy, especially with untreated tinea pedis reservoir
Pityriasis versicolor pigment changes can take months to normalise even after successful treatment

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