Fungal Skin Infections Flashcards
What are dermatophyte infections (tinea/ ringworm)?
-Extremely common, particularly in primary care, with up to 50% of individuals aged over 50 having had an infection.
-In parts of Africa the point prevalence in some surveys of children is over 30%.
-The terminology is confusing in that they often have a name for particular sites (tinea capitis for the scalp, tinea barbae for the beard area, tinea pedis for the feet etc)
Overview of tinea infections
-Presentation: annular erythematous scaly eruption with or without pustules, with an apparently more active edge (hence the phrase ‘ringworm’). If inflammation is marked, consider whether it could be an animal ringworm infection. The differential is often eczema.
-Investigation: Scrape the lesion for mycological confirmation of your diagnosis
-Management: topical agents (azole creams: miconazole, ketoconazole) or topical terbinafine
Exceptions to the use of topical azole in dermophyte infections
-Scalp
-Nail
-Tinea Incognito
Describe scalp dermophyte infection
-Common in children, presents with erythema and alopecia, scale and pustules, and sometimes a boggy inflammatory swelling known as a kerion.
-Secondary infection of the primary dermatophyte infection may also occur
-Topical agents alone are usually ineffective and systemic treatment is required with either oral terbinafine (or systemic azoles or griseofulvin)
Describe dermatophyte infections of the nail
-Presents with onycholysis, ridging, pitting, and dystrophy of the nail. Hyperkeratosis.
-Again, topical agents do not work (well enough), and systemic treatment with either terbinafine or one of the systemic azoles is required. Liver effects.
-Treatment for nail infection is prolonged, more so for the feet than the finger nails (3 or more months for the former)
-Never commence treatment without mycological confirmation of your diagnosis. Hyphae in scrapings/ clippings dissolved in potassium hydroxide
-Never use systemic agents for nail dermatophyte infections without the support of positive mycology, because you expose patients to adverse drug effects for no benefit, and clinical diagnosis is frequently inaccurate
Describe tinea incognito
-When a dermatophyte skin infection is misdiagnosed as eczema (usually) and treated with topical corticosteroids.
=Initially both doctor and patient think things are getting better, but the steroids dampens down the appropriate immunological response, resulting in spread of the fungal infection, which subsequently flares with marked erythema and pustules when the steroids are stopped.
=Remember, dermatophyte infections can easily be confirmed by scraping some of the scale, and sending it for microscopic examination and culture (fungus stays viable for months so it can just be put in the post).
-Dermatophyte infections may have an annular structure, but there are many other causes of rings apart from dermatophytes (e.g. the Olympic symbol)
Overview of Candida
-Risk factors: diabetes, steroids or immunosuppressive therapy, pregnancy or occult neoplasia.
-Angular stomatitis/ cheilitis at the corners of the lips, may reflect ill-fitting dentures.
-Responds to a steroid/azole combination cream
Describe cutaneous candida
-Clinically favours warm moist skin, such as under the breasts or in folds of skin due to obesity (intertriginous areas)
-Usually presents as well demarcated bright red areas, with a little bit of scaling and satellite lesions
-Differential will include psoriasis and eczema
=In children wearing nappies, a differential is an irritant dermatitis secondary to ammonia.
=If the depths of the folds are affected, then candida is likely, as the ammonia tends not to permeate the skin folds.
-Combination azole and steroid creams are useful.
-In the male, candida can cause balanitis, which can be spread by sexual intercourse
What is Pityriasis versicolor?
-Yeast infection of the yeast genus ‘Malassezia’
-Sometimes referred to as tinea versicolor, but tinea should be restricted to dermatophytes not yeasts
-Pityriasis versicolor is an extremely common disorder, most commonly seen in young people and often first noticed after a summer holiday
Clinical features and treatment of pityriasis versicolor
-Dull, red / light brown, scaly plaques on the upper chest and back, which when scratched release abundant scale. Annular silvery hypopigmentation
=Can cause seborrhoeic dermatitis
-If the scale is examined with a drop of potassium hydroxide, abundant Malassezia are seen, both as hyphae and yeast forms (‘spaghetti and meatballs’)
-Upon exposure to sunshine the affected areas often appear paler than the surrounding skin and either with or without treatment, the disorder progresses to leave pale, non-scaly, areas which are often most apparent following sun exposure.
-Treat with imidazole shampoo (ketoconazole)
