Dermatophytic Infections

1. T. pedis  the most common tinea (30- 70%). It starts off mild and then can go into remission or into secondary bacterial infection which looks really really gross. T. pedis only started being such a problem in the last 200 years because of people wearing tight, non-airy shoes. It’s more common in adults and in people with a genetic predisposition. Caused by T. rubrum, mentagrophytes, and E. floccosum. The treatment is creams, and if that don’t work then systemic antifungals.

2. T. unguium  starts off in a corner and spreads, sometimes even to other toes. Usually caused by T. rubrum. The only effective treatment is systemic antifungals for several months and monitor liver functions. 5-10% of the population get it.

3. T. capitas  scalp infection, usually caused by microsporum and trichophyton. Mostly affects young people and African Americans. The incidence has been decreasing, probably due to better sanitary conditions. The infection smells like urine and mouse droppings. There are infections that are anthrophilic and live inside the hair shaft and other live on the outside. They weaken the hair and cause it to break. Prevention includes avoiding oiling or braiding hair, not sharing combs or hats, going to clean barbers, avoid overcrowding, skin trauma, and animals. Treatments over the years have been really weird. In Paris, they covered the head with tar and then pulled it off. Then they used X-rays but that led to baldness and brain tumors. Now we use azoles for 2-4 weeks or griseofulvin for 6-8 weeks.

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5. T. cruris  affects the groin and perineum, usually caused by T. rubrum, and E. floccosum. Usually men get it. It spares the penis and scrotum. It can be prevented by using loose cotton clothing, sterilize towels and underpants, and losing weight. It’s treated with topical and systemic antifungals.

6. T. corporis  caused by T. rubrum, and T. mentagrophytes. People have it and scratch the lesions and pass it on to other parts of the body. The middle of the lesion is smooth and the edge is bumpy due to an immune response.

There are skin infections that can be confused with dermatophytic infections. These include T. versicolor is caused by yeast. It makes someone have spots that are darker or lighter than thir skin and comes out in the sun. Candida will be dealt with later. Sebhorreic dermatitis is probably caused by an exaggerated T-cell response to yeast. Eczema is an immune response seen in 10-20% of the population, especially babies. Psoriasis is scaling, thickening, and inflammation of the skin.

Diagnosis:

The doctor takes a scraping or clips the nail  adds KOH and ink, this melts keratin, but don’t harm the hyphae  adds fluorescent coloring  if there’s fungi they stand out under UV light. In the lab it grows slow at low temperatures. Chloramphenicol is added to kill bacteria and cyclohexinide to kill fast growing fungi. Then the lab looks at the plates, but interpretation is varied and experience is needed. On DTM plates, dermatophytes form red halos because they change the pH. An important thing to know for the boards is that they used to use a wood lamp (which is a UV light) and hold it to the hair. If the hair fluoresces then it’s a fungal infection.

Category: Dermatology Notes