Cutaneous fungal infection

In this CCC we will be discussing dermatophyte infections as well as pityriasis versicolor.

DERMATOPHYTE INFECTIONS

Dermatophyte infections or tinea are skin infections from fungi that grow on the skin and require keratin for their growth. They may vary depending on the site of infection.

🦠 Pathophysiology and causative agents

Dermatophytes may be spread from person-to-person, soil, animals. Once they infect a break in the skin, they germinate and produce keratinases to invade the superficial skin layers. As they require keratin for growth they are restricted to hair, nails, and superficial skin but are unable to infect the mucosal surfaces.

The 3 species of fungi that can cause tinea infections are:

1. Microsporum spp.
2. Trichophyton spp.
3. Epidermophyton spp.

🔢 Classification

We can classify the infections based on their location:

TINEA CAPITIS

Tinea capitis is also known as scalp ringworm. It is the infection of the scalp hair follicles and surrounding skin.

It is usually caused by Trichophyton tonsurans in the UK cities but may also be via Microsporum canis which is transmitted from cats and dogs and is more common in rural UK.

😷 Presentation

• Scaling and itching of scalp
• Patchy alopecia
• Pustular, crusty abscess - this is known as a kerion.

🔍 Investigations

• Scalp scrapings for microscopy and culture
• Wood’s lamp - Microsporium canis readily turns a green colour under fluorescent light.

🧰 Management

While waiting for cultures, start off with empirical antifungals:

→ 🥇 Urban areas - terbinafine for 4 weeks (for suspected trichophyton infection).

→ 🥇 Rural areas - griseofulvin for 4-8 weeks (for suspected microsporum infection).

Once culture results are available:

• Trichophyton infection - terbinafine
• Microsporum infection - griseofulvin (an alternative would be itraconazole)

🥇 These should be combined with ketoconazole shampoo to reduce the risk of transmission. It should be used twice weekly for 2-4 weeks.

TINEA CORPORIS & TINEA CRURIS

Tinea corporis is the fungal infection of the body while tinea cruris is the fungal infection of the groin. It usually occurs when there is already infection of the hands, feet or nails.

🦠 Causative agents

Body infection is usually caused by:

1. Trichophyton rubrum
2. Trichophyton interdigitale

Groin infection is usually caused by:

1. Trichophyton rubrum
2. Trichophyton interdigitale
3. Epidermophyton floccosum

It is usually transmitted by contact with infected person or animal, soil or indirect contact with fomites (inanimate object carrying disease such as towels, clothes or bed linen)

⚠️ Risk factors

• Hot and humid climates
• Tight fitting clothing
• Obesity

• Hyperhidrosis (excessive sweating)
• Immunocompromise

😷 Presentation

• Scaly, itchy skin
• Red or pink ring-shaped patches on body - they are usually clear in the center and red and scaly on the outside.
• Red or brown plaques on groin - they have no central clearing. Most commonly in the inguinal folds, medial thighs, buttocks and perianal skin.

🔍 Investigations

Clinical diagnosis is sufficient. However, if there is severe/extensive disease or if it has an atypical appearance then we should perform:

• Skin sampling for microscopy and culture

🧰 Management

• Advise patients on:
1. Wearing loose-fitting clothes
2. Maintaining hygiene
3. Not sharing towels
4. Washing clothes and linen frequently

Antifungal treatment

• 🥇 A topical antifungal is first-line for mild disease.
• Terbinafine cream
• Imidazole cream - such as clotrimazole, miconazole, econazole.
• 🥇 If there is extensive disease, oral terbinafine is first-line.
• Associated inflammation might warrant hydrocortisone 1%.

TINEA PEDIS

Tinea pedis, commonly known as athlete’s foot is a fungal infection of the feet and toes.

🦠 Causative agents

It is primarily caused by trichophyton rubrum (most common), trichophyton interdigitale and epidermophyton floccosum.

⚠️ Risk factors

• Walking on contaminated floors - such as communal showers, swimming pools and saunas.
• Hot and humid climates
• Tight fitting clothing

• Obesity
• Hyperhidrosis (excessive sweating)
• Immunocompromise

😷 + 🔢 Presentation and classification

There are 3 main types:

Interdigital type

Found between the toes. Typically it starts on the lateral digits (4th and 5th) and moves medially.

• White or red appearance
• Fissured
• Scaling skin

Moccasin/dry type

More diffuse and chronic. Found on the sole. The dorsum of the foot is unaffected usually.

• Erythema
• Scaling
• Hyperkeratosis

Vesicobullous type

Found mainly on the arches and soles of feet.

• Vesicles and blisters
• Bullae
• Erythematous base

🔍 Investigations

Clinical diagnosis is sufficient. However, if there is severe/extensive disease or if it has an atypical appearance then we should perform:

• Skin sampling for microscopy and culture

🧰 Management

Antifungal treatment

• 🥇 A topical antifungal is first-line for mild disease.
• Terbinafine cream
• Imidazole cream - such as clotrimazole, miconazole, econazole.
• 🥇 If there is extensive disease, oral terbinafine is first-line.
• Associated inflammation might warrant hydrocortisone 1%.

TINEA UNGUIUM/ONYCHOMYCOSIS

Tinea unguium also known as onychomycosis is a fungal infection of the nail plate, nail bed, root of the nail or the entire nail. It affects the toenails 7x more than the fingernails.

🦠 Causative agents

• Dermpatophyte infections - these make up 85-90% of onychomycosis infections.
• Trichophyton rubrum
• Trichophyton mentagrophytes
• Candida spp. - these make up 5-10% of onychomycosis infections, however, they make up about 50% of cases of fingernail onychomycosis.
• Other infections include aspergillus, fusarium, scopulariopsis and a few others.

⚠️ Risk factors

• Family history
• Elderly age
• Concomitant fungal skin infections
• Diabetes mellitus, PAD, Raynaud’s phenomenon

• Immunocompromise
• Repetitive nail trauma
• Occlusive or poor fitting footwear

😷 Presentation

It most commonly affects the 1st and 5th toenails.

1. Discolouration of the nail
1. Superficial white - flaky white patches on top of the nail plate.
2. White/yellow - streaks may appear on the lateral aspects of the nail or spots may appear in the proximal growing end.
2. Subungual hyperkeratosis - scaling under the distal nail causing discolouration, opaqueness and thickening.
3. Dystrophic nail - marked thickening and destruction of the nail.
4. Associated paronychia

🔍 Investigations

• Nail clippings/scrapingsfor microscopy and culture

🧰 Management

Antifungal treatment is not necessary if the infection is asymptomatic and the patient is not worried about cosmetics. Advise the patient to keep their nails trimmed short and to wear well-fitting shoes.

Antifungal treatment - may be provided if walking is uncomfortable, psychological distress or if there is risk of complications (with comorbidities).

• Amorolfine 5% nail lacquer - is the first-line option. It should be applied once or twice weekly for 6 months on fingernails or 9-12 months on toenails.

PITYRIASIS VERSICOLOR

Pityriasis versicolor (PV), also known as tinea versicolor is a superficial cutaneous fungal infection caused by the fungus Malassezia furfur (which was previously known as pityrosporum ovale). It is not only furfur that cause PV, but many other species such as malassezia globosa and malassezia sympodialis.

It is most common in hot and humid climates, especially during the summer months and occurs more commonly in teens and young adults.

Pathophysiology

PV is characterised by alterations to skin by either hyperpigmentation or hypopigmentation.

• Hyperpigmentation - this is due to abnormally large melanosomes and hyperaemia in response to the infection.
• Hypopigmentation - due to damage to melanocytes and decreased melanosomes. Inhibition of tyrosinase, an enzyme involved in melanin production is inhibited by decarboxylic acid. This explains why repigmentation can take months-years even after successful treatment.

⚠️ Risk factors

😷 Presentation

It most commonly affects the trunk area.

• Dyspigmentation - can be either hyperpigmented or hypopigmented.
• Scale
• Lack of pruritus - it is rarely itchy, and if so only mildly.

🔍 Investigations

Clinical diagnosis

🧰 Management

• 🥇 Ketoconazole 2% shampoo - applied once daily for up to 5 days. It should be lathered on and left on the skin for 3-5 minutes.

If it is simply a small area infected, imidazole creams can be applied twice a day instead.