USMLE® Step 1 style questions USMLE
A 44-year-old woman comes to her primary care physician for evaluation of unpleasant taste progressing to moderate loss of taste in the past week. She was treated with oral cephalexin for a urinary tract infection several weeks ago and finished her course of treatment before the onset of symptoms. She has no significant past medical history. Vitals are within normal limits. Physical examination shows white plaques on the buccal mucosa, palate, and tongue. The physician can scrape several plaques using a tongue depressor that reveals underlying erythema with light bleeding. The scrapings are prepared for pathological examination. Which of the following is most likely to be observed on microscopy?
Of these, the most common one is C. albicans. Candida is found throughout the body; it likes warm, moist environments like the mouth, the diaper region of babies, and in women it can be found in the vagina.
Now, it’s normal for microbes - bacteria, fungi, and viruses - to live all over the body, but each microbe is slightly different in terms of whether it’s colonizing the body - in other words just living and not causing any problems, or whether it’s infecting the body, causing some degree of tissue damage or destruction.
An important factor is exactly how much of a microbe is present.
Candida is considered an opportunistic microbe.
When the amount of Candida is relatively low, it's harmless.
Now, Candida can exist in multiple forms - it’s a bit like a chameleon.
Sometimes the cells can appear round or oval and these are called yeast cells, other times it can appear like hyphae where it looks like long thin filaments - kind of like a segmented cactus plant.
It can also take an in-between appearance called pseudohyphae.
Each of these morphologies or “looks” reflect the same Candida cells that are expressing different protein profiles, and they give the cells different properties.
Candida typically lives on the skin or mucous membranes, and when it starts to overgrow it can damage nearby tissue.
The result is destruction of the stratified squamous epithelium layer, which is the outermost layer of the skin or mucous membranes.
This causes accumulation of the destroyed cells and the keratin protein that fills that outermost layer, forming a white lesion, called a pseudomembrane, that looks kind of like “cottage cheese”.
The white lesions aren’t typically painful and they can be scraped away with a tongue depressor, leaving behind a red mucosal base which sometimes bleeds.
It can also be related to an immunosuppressive condition like diabetes or HIV, or from immunosuppressive medical treatments like steroids - including inhaled steroids, as well as radiotherapy or chemotherapy.
In a lot of situations there’s a mixed pattern of injury with both a pseudomembranous and erythematous component.