USMLE and COMLEX Prep: Physiology of Cystic Fibrosis

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Session 10

This week, we’re going to tackle respiratory stuff, specifically about cystic fibrosis. Again, we’re joined by Dr. Andrea Paul from Board Vitals. This podcast is part of the MedEd Media Network. Please share us with fellow residents as well as medical students and premeds who are also on this path towards becoming a physician.

[02:41] Question of the Week:

An 8-year-old boy is presenting with a history of recurrent respiratory infections. His parents are complaining that the patient complains of fatty stools. Positive sweat chloride test confirms his diagnosis. The patient will likely have difficulty storing which of the following:

(A) Folate

(B) Vitamin B12

(C) Vitamin C

(D) Vitamin D

(E) Zinc

[03:11] Thought Process

Most students would easily be able to identify the condition here would be cystic fibrosis. But this is not what they’re asking. So the “sweat chloride” would be a strong buzzword painting that picture of cystic fibrosis.

Recurrent infection and fatty stools were also mentioned so that would make you think along the lines of fat digestion and fat storage. What happens here is it brings damage to the pancreas which impairs the production of fat-digesting enzymes or pancreatic enzymes. So you have decreased ability to digest as well as decreased mobility to store fat. This would be down the fat-soluble vitamin route. Then you should be able to pretty quickly identify Vitamin D.

[04:35] Other Possible Questions

They may ask about inheritance patterns with cystic fibrosis. They love to talk about microbiology with cystic fibrosis. What type of bacteria is commonly found in the sputum of patients with cystic fibrosis? They may also ask about the GI symptoms associated with it. They could ask the background of the symptoms and what tests could be done or what would be found for further diagnostics or imaging of the patients with symptoms that sound suspicious for cystic fibrosis. It could be the whole spectrum of things from presentation all the way through diagnosis and treatment for cystic fibrosis.

[05:53] New Therapies Coming Out

With so many new therapies related to cystic fibrosis right now, it’s hard to say as to how long it would take for these new therapies to be included in the tests. If it’s something that came out within that year, it could just be added as a beta question and not necessarily counted in the grading, and then they’re just going to add it as a graded component the following year.

[07:05] More Things About Cystic Fibrosis

When thinking about presentation, look at the symptoms of a patient with cystic fibrosis such as recurrent infections, chronic productive cough, shortness of breath, GI symptoms, especially in infants and young children where you have probably greasy stools, malabsorption-type symptoms. There could also be pancreatitis.

On exam, if the kids are not diagnosed yet, you would see failure to thrive. The question might describe that the skin tastes salty or their sweat tastes salty, another hint that they could have cystic fibrosis. Then think about things like chest x-ray seeing hyperinflation. They could put in there what test should you use or maybe they’d mention the results of that test.

In terms of genetics, think about other primary cellular dyskinesia or other immunodeficiencies with recurrent infections. Those are the things to keep in mind as differentials.

Also, think about prognosis and common complications. There are long term complications of cystic fibrosis such as infertility, drug-resistant infections from having antibiotics chronically from childhood.

[09:10] Final Thoughts

It could be overwhelming for students with all these bits and pieces of information. But it’s doable. You’re not expected to remember every single piece. The goal is to memorize them all but once you get to a certain point of knowing the most important or the most commonly tested effects, oftentimes, the other things are tied in there. So once your mind goes to the right direction, you’d have all these other associated things coming in.

'Once you get the basics down, the rest is in there.'Click To Tweet

[10:50] Board Vitals

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