Dermatophytosis

Introduction¹

Dermatophytosis (tinea) infections are fungal infections caused by dermatophytes - a group of fungi that invade and grow in dead keratin. Several species commonly invade human keratin and these belong to the Epidermophyton, Microsporum and Trichophyton genera. They tend to grow outwards on skin, producing a ring-like pattern - hence the term 'ringworm'. They are very common and affect different parts of the body. They can usually be successfully treated but success depends on the site of infection and on compliance with treatment.

See the separate Tinea Capitis, Fungal Nail Infections, Pityriasis Versicolor and Candidiasis articles.

Pathophysiology²³

• Infection is limited to the dead layers of skin but encouraged by a damp and warm local environment.

• The infection can be transmitted to humans by anthropophilic (between people), geophilic (from soil) and zoophilic (from animals) spread.

• The most common organisms are:
  

  • Trichophytons rubrum, Trichophytons tonsurans, Trichophytons interdigitale and Trichophytons mentagrophytes.

  • Microsporum canis.

  • Epidermophyton floccosum.

• Clinical classification is according to site:
  

  • Scalp - tinea capitis.

  • Feet - tinea pedis.

  • Hands - tinea manuum.

  • Nail - tinea unguium (or onychomycosis).

  • Beard area - tinea barbae.

  • Groin - tinea cruris.

  • Body including trunk and arms - tinea corporis.

Epidemiology

Infection is very common all over the world. Some types are more common than others, with tinea pedis being most common in adults and tinea capitis the most common in children. Onychomycosis is also extremely common.

Presentation²

History

• Itching, rash and nail discolouration are the most common symptoms of tinea infection.

• Hair loss occurs with tinea capitis (mainly a disease of children).

• Complications such as secondary infection (cellulitis and impetigo) can lead to symptoms.

• It is common in people who play contact sports.

• It occurs in immunocompromised patients.

Examination

• Tinea pedis⁴:
  

  • It particularly affects the web of the toe where skin may be macerated and erythematous.

  • It commonly affects the plantar surface of the foot. Erythema, vesicles and pustules can occur.

  Tineas pedis - between toes

  

  By Falloonb on en.wikipedia, Public domain, via Wikimedia Commons

• Tinea capitis⁵:

  • It can cause hair loss with broken hairs at the surface (as distinct from alopecia areata).

  • Clinical appearance is variable, including scaly, crusting, pustules and/or black dot alopecia.

• Tinea unguium (onychomycosis)⁶:

  • Onycholysis or separation of the nail from the nail bed commonly occurs.

  • Nail dystrophy with thickening and discolouration of the nail develops.

• Tinea corporis⁷:

  • The skin lesions have annular scaly plaques with raised edges.

  • There may be vesicles and pustules.

  • Typically lesions are on exposed skin of the trunk, arms and legs (see 'Differential diagnosis', below).

  • More unusually the lesions can appear as overlapping concentric circles (tinea imbricate) or even herpetiform subcorneal vesicles or pustules (bullous tinea corporis).

Tinea corporis

By Corina G., Public domain, via Wikimedia Commons

• Tinea manuum:
  

  • Usually with tinea pedis.

  • Typically just affects one hand.

  • Scaling and redness are prominent.

  • Incorrect diagnosis and use of steroid may eventually exacerbate the infection.

• Tinea cruris⁸:
  

  • Usually occurs in men.

  • Often tolerated for some time before presentation.

  • Typically erythematous with central clearing and raised edge.

• Tinea barbae⁹:
  

  • Affects the beard area.

  • Redness, scaling and pustules are common.

Differential diagnosis⁷

Other annular rashes are often confused with tinea infections. Eczema and psoriasis are commonly confused with tinea. Pityriasis versicolor occurs all over the trunk while candida occurs as a flexural rash at extremes of age or in the immunocompromised, those with diabetes or patients on antibiotics.

Treatment with topical steroids often causes confusion, making tinea less scaly and more erythematous. Steroid use also makes the 'active' edge and the inactive centre less distinct (tinea incognito). Clinically the diagnosis can be difficult but, if it is a possibility, take scrapings for mycology. Other fungal infections look nothing like tinea. Other conditions to consider include:

• Contact dermatitis

• Seborrhoeic dermatitis

• Intertrigo

• Erythrasma

• Mycosis fungoides

• Alopecia areata

Investigations¹⁰

• Microscopy of skin and nail specimens may reveal hyphae and spores.

• Fungal culture can identify the species but is not always reliable and it can take six weeks to obtain results.

• Ultraviolet light (Wood's light) is useful for tinea capitis especially. Fluorescence is produced by the fungus. Fluorescence is not seen with tinea corporis or tinea cruris.

• Rarely, a biopsy may be needed if the case is atypical or not responding to treatment.

Associated diseases

Diabetes, immunocompromised states, atopy and Cushing's syndrome have all been associated with fungal infections.

Management⁴⁵⁷¹⁰

• Offer advice on hygiene measures:
  

  • Keep affected skin cool and dry.

  • Wear cotton, absorbent clothing.

  • Avoid scratching affected skin.

  • After washing, dry thoroughly.

  • Do not share towels, and wash frequently, to reduce the risk of transmission.

  • Cover feet in communal bathing pools, changing areas and gymnasiums if feet are affected.

  • Continue school and sporting activities.

• See the separate Antifungal Medications article.

• Topical agents containing a corticosteroid are not usually necessary. They may be used if there is a lot of skin inflammation. They should be used for a week only.

• Referral may be needed if diagnosis is in doubt.

Complications

The main complication is secondary bacterial infection. Hair loss is a complication of tinea capitis. Pain and difficulty with shoes can result from onychomycosis.

Scarring is uncommon but more likely in people with pigmented skin. Scarring usually fades with time. Skin protection such as using a moisturiser cream and sunscreen can be helpful. Extensive or severe scarring may need further treatment, such as using laser therapy.

Prognosis

Excellent with good compliance and subsequent precautions to avoid repeat infection.

Prevention

• Good skin hygiene.

• Good nail hygiene.

• Avoiding prolonged wetting or dampness of the skin and feet.

• Avoiding trainers, which can retain sweat and promote a warm, moist environment.

• Treatment of tinea pedis - helps prevent onychomycosis⁶.

• Wearing clean, loose-fitting underwear.