Fungal Nail Infections - Onychomycosis.
Distal and lateral subungual onychomycosis (DLSO) is the commonest form and is virtually always caused by dermatophytes. Infection starts under front of nail or nail fold and extends under the nail to involve the whole structure. Can either affect a healthy nail or one already diseased, e.g. by psoriasis. Approx. 80% of cases occur on the feet, especially on big toes often affecting both toe and fingernails. Initially presents as white patch on the under surface of the nail and nail bed but becomes discoloured to brown or black. Progression can incur within weeks or more slowly over months or years with the nail becoming opaque, thickened and cracked, friable and raised from the nail bed.
Superficial white onychomycosis (SWO) Usually caused by dermatophyte invading surface of dorsal nail plate presenting as white chalky plaque on proximal nail plate almost exclusively on the toenails. Nail plate may become eroded and even lost.
Proximal subungual onychomycosis is almost always associated with immunocompromised patients presenting as a white spot beneath the proximal nail fold which eventually fills the lunula occurring most commonly on toenails. Eventually can involve whole of the under surface of the nail plate.
Candida onychomycosis occurs as different types:
Candida paronychia – initially appears as oedema, erythema and pain of the nail fold from which pus can be expressed at times. Also nail plate becomes dystrophic with patches of opacification or discolouration (white, yellow, green or black) with transverse furrows. Usually, pressure on the nail causes pain. Most cases are on fingernails usually middle finger.
Subungual abscess with DLSO occurring in the setting of onycholysis (see above).
Acute paronychia Erythema, swelling and throbbing pain in the nail fold caused by bacterial infection, e.g. Staph. aureus and group A Strep.
Chronic paronychia commonly occurs in patients whose hands are constantly in water with repeated minor trauma damaging the cuticle so that irritants can further damage the nail fold. Proximal and lateral nail folds show erythema and oedema with loss of cuticle and part of proximal nail fold separating from nail plate. Commonly becomes infected especially with C. albicans. Eventually nail fold retracts becomes thickened and rounded. There are episodes of painful acute inflammation often due to infection between the proximal nail fold and nail plate from which pus may drain. Over time, lateral edges of nail plate become irregular and discoloured and eventually entire nail plate becomes involved showing numerous transverse grooves. Treatment is to remove source of irritation, topical steroids and weekly doses of fluconazole.