Cutaneous fungal infections (dermatophytosis, pityriasis vesicolor) Flashcards
What are the clinical features of fungal foot infection?
- dry
- red
- scaly
- itchy
- usually starts between the toes and speads to the soles
Who is most affected by athlete’s foot?
Men >women >children
How is athlete’s foot spread?
Indirect and direct contact
What causes athlete’s foot?
Dermatophyte (tinea pedis)
What conservative measures can be used in management of athlete’s foot?
- wearing open shoes
- good foot hygiene
- wearing cotton socks (rather than synthetic or no socks at all)
- drying feet thoroughly
- not sharing towels
What is Whitfield ointment?
Why is it used for athlete’s foot?
Whitfield ointment = benzoic acid and salicylic acid
It is a useful keratolytic treatment but prescribed less now.
Which medical treatments are used for athlete’s foot?
Topical:
Terbinafine 1%(1st line)
+/- Aluminium acetate foot soaks BD
Imidazoles e.g. clotrimazole, ketoconazole, miconazole (2nd line)
Systemic:
Terbinafine (3rd line) - but must monitor for hepatotoxicity (LFTs)
Define dermatophytosis.
Superficial fungal infection with varying presentation depending on site. Dermatophytes are fungal organisms that require keratin for growth.
These fungi can cause superficial infections of the hair, skin, and nails. Dermatophytes are spread by direct contact from other people, animals, soil, and from fomites.
How common are dermatophyte infections?
Varies
Tinea pedis is the most common of the superficial fungal infections, occurring in up to 70% of adults
Tinea capitis is most common in children and tinea cruris in adolescents and adult men.
How do dermatophyte infections spread?
- Directly from one person to another
- Soil to human
- Animal to human
What are the risk factors for dermatophyte infections?
Host factors
- Genetic susceptibility, including atopy
- Ethnicity
- Immunosuppressive illnesses or medications (e.g., HIV infection, corticosteroids)
- Presence of other skin diseases that disrupt the epidermis (e.g., atopic dermatitis)
- Other illnesses that predispose to skin infection, including diabetes mellitus and peripheral vascular disease.
Local factors
- Sweating
- Occlusion
- Occupational exposure
- High humidity (tropical or semi-tropical climates)
- Exposure to infected pets or farm animals, infected fomites, skin contact with the floors of public bathing facilities
- Contact sports such as wrestling.
What is the pathophysiology of dermatophyte infections?
- Exposure to infected desquamated cells occurs by direct contact
- Inoculation occurs through breaks in the skin
- Dermatophyte fungi enter, germinate and produce keratinases
- They invade the superficial skin layers
- The fungi require keratin for growth
- The are restricted to hair, nails, superficial skin
What is the common name for dermatophyte infection?
Ringworm
What are the general clinical features of dermatophyte infection?
- Rash - annular, central clearing with an active border of inflammation. Satellite lesions.
- Scaling lesions with patchy alopecia
- Follicular pustules
- Fissuring, maceration and scaling in interdigital spaces of the fourth and fifth toes
What is the diagnosis?
Psoriasis - annular lesion on the elbow, with a silvery scale. No central clearing. Microscopic examination with potassium hydroxide revealed no fungal elements.
What are the clinical features of tinea capitis?
- a cause of scarring alopecia mainly seen in children
- if untreated a raised, pustular, spongy/boggy mass called a kerion may form
- most common cause is Trichophyton tonsurans in the UK and the USA
- may also be caused by Microsporum canis acquired from cats or dogs
How do you diagnose tinea capitis?
Wood’s light exam - Lesions due to Microsporum canis casuse green fluorescence.
Scalp scrapings - the most useful investigation
What is the management of tinea capitis?
Oral antifungals for 4-6 weeks
Terbinafine - for trichophyton tonsurans infections
Griseofulvin - for Microsporum infections
Topical ketoconazole shampoo - given for first 2 weeks to reduce risk of transmission
What are the most common organisms causing tinea capitis?
Trichophyton tonsurans - most common
Microsporum canis - from cats or dogs
What are the most common organisms causing tinea corporis?
Trichophyton rubrum and Trichophyton verrucosum e.g. from contact with cattle
Which organism causes of ringworm do not fluoresce under Wood’s lamp?
Trichophyton species
What is the management of tinea corporis?
1st line: Topical terbinafine 1% for 1-3 weeks
2nd line: Other topical antifungal e.g. miconazole 2% for 2-4 weeks and 1-2 weeks after infection subsides
3rd line: Oral antifungal e.g. terbinafine 250mg oral OD 2-4 weeks
What is the management of tinea unguium?
1st line: Systemic terbinafine therapy - 12 weeks for toenails, 6 weeks for fingernails
2nd line: Systemic azole or topical e.g. fluconazole or ciclopirox topical
What are the complications of dermatophyte infections?
- Kerion
- Bacterial infection associated with tinea pedis
