Fungal Skin Infections/Dermatophytosis

Fungal Infections/Dermatophytosis

·        = Tinea

·        Fungal infections of animal (zoophilic) origin: These include “ringworm” (which causes a scaling macule – not a ring – and there is no worm!). Usually in children, for example from cows, dogs, cats or mice

Clinical Description

·        Fungal infections usually itch.  Have a raised scaling margin that extends outwards

·        There are several classical presentations:

o  Tinea Cruris: in the groin. Mainly affects men. Sharp margin. On thighs or buttocks may get follicular pustules. If feet involvement as well then systemic treatment, otherwise topical

o  Tinea Capitis: Scalp. Invasion of hair shaft. Causes alopecia. Usually M Canis. Usually children aged 3 – 7, nearly always cervical occipital lymphadenopathy. Needs systemic treatment (topical doesn‟t penetrate hair shaft).

o  Athlete‟s Foot/Tinea pedis: on the feet (usually lateral toe clefts – compared with eczema which in medial toe clefts). Increased sweating predisposes to fungal infection. It can be spread to the sole with a powdery scale. To hands by itching, where it presents with a dry, hot rash on one palm, with well defined lesions with a scaling edge

o  Tinea Corpus: on the trunk. Presents with an erythema and itching, and a well defined, scaling edge. May not itch

o  Tinea manuum: Hand.  Almost always a pre-existing foot infection.

o   Fungal infection of the nail (Onychomycosis): occur mainly in adults, usually in their toenails (fingernails uncommon, ?psoriasis), and especially following trauma. The nails become thickened, yellow, and crumble, usually asymmetrically. The changes occur distally, and move back to the nail fold (compared with psoriasis, which is symmetrical and moves distally from the nail fold)

o  Tinea Incognito: Fungal infection treated with steroids. Stops inflammation but fungus slowly spreads ® follicular pustules etc.

·        Tinea Versicolor:

o  Infection due to a commensal yeast Malassezia Furfur (= pityrosporum ovale. Not a fungus). In young adults, causes hypo- or hyper-pigmented macules with powdery scale, on upper trunk, upper arms and neck. Slightly itchy 

o  Differential diagnoses:

§  Vitiligo: but pure white lesion (amelanotic), no scaling

§  Pityriasis alba: Usually children and on the face.  Tinea Versicolor rare in children

o  Treatment: Imidazole cream, sporanox, selsun shampoo

Diagnosis

·        Consider in any patient where isolated, itching, dry and scaling lesions occur for no reason (e.g. no history of eczema). Fungal lesions are usually asymmetric. Clippings or scrapings can be sent for culture

Pathogenesis

·        Common: Microsporum Canis (from cats, fluoresce under Wood‟s light), Trichophyton rubrum, and

·        Trichophyton mentagrophytes

·        Less common: Trichophyton tonsurans, Epidermophyton floccosum, Trichophyton erinacei 

·        Fungi consist of thread-like hyphae that invade keratin (yeasts do not have hyphae). Vegetative spores (conidia) develop in culture. When immune response is impaired, superficial infections may invade deeper tissues

Management

·        Topical Treatment: imidazole preparations, such as clotrimazole and miconazole. Dusting preparations are also available. Terbinafine is available as a cream

·        Systemic Treatment: Diagnosis should be confirmed before commencing treatment. Terbinafine (250mg, once daily PO) for 2 to 6 weeks for skin infections and 3 months for fingernail infections, 6 months for toe nail infections. (Pregnancy and lactation are relative contraindications). Can take itraconazole 1 week per month for 3 months (200 mg bd) ® ¯ side effects. Takes 12 – 18 months to grow a new nail. Given length of treatment, confirm with nail scraping for culture first.