THE USMLE TIMES - #101
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Welcome to the 101 issue of The USMLE Times! Thank you to all of our supporters—new and old!
I’m Paul Ciurysek, MD, founder of The USMLE Guys, and this is The USMLE Times. This daily newsletter aims to provide you with super high-yield USMLE concepts that are commonly tested on exam day. All content is FREE! If you’d like to work with me and my team, please see the options at the bottom of today’s newsletter. If you’d like to support my efforts, please share the newsletter with a friend.
Here’s what’s on tap for issue #101 of the USMLE Times:
3-part question of the Week (Nutritional Deficiencies)
This week’s video training (Memorizing NBMEs As A Strategy)
Question deep-dive & breakdown
Let’s dive in!
A 14-year-old male comes to the clinic with a rash around his mouth, nose, eyes, and on his hands and feet. He also mentions a decreased appetite, delayed growth, and a history of frequent infections. On physical examination, delayed sexual development is observed. Laboratory findings reveal low serum alkaline phosphatase levels.
Q1: Which of the following is the most likely diagnosis?
A) Perioral dermatitis
B) Acrodermatitis enteropathica
C) Atopic dermatitis
D) Marasmus
E) Kwashiorkor
Q2: What is the primary underlying cause of the condition diagnosed in Q1?
A. Inhibition of carbonic anhydrase
B. Inhibition of the sodium-potassium pump in the basolateral membrane
C. Inhibition of the sodium-potassium-chloride cotransporter
D. Inhibition of the sodium-chloride cotransporter
E. Inhibition of prostaglandin synthesis
Q3: Which of the following laboratory findings would further support the diagnosis made in Q1?
A) Low serum zinc level
B) Elevated serum iron level
C) Low serum folate level
D) High serum ferritin level
E) Elevated serum magnesium level
The answer & question breakdown is at the bottom of the post 👇🏼
🔗 LINKS TO RECENT POSTS
USMLE Times Issue #100 - READ HERE
USMLE Practice Question #89 - TRY IT HERE
USMLE Practice Question #88 - TRY IT HERE
This week’s recommended video 👇🏼
ANSWER + QUESTION BREAKDOWN
The mental model used to answer this question comes from our detailed test-taking skills masterclass (check it out if you want to elevate your USMLE test-taking skills) Here’s how to think through this question:
This is a new 3-part variation on the traditional USMLE-style question we’re testing. The goal with this format is to get more complex (1st order, 2nd order, 3rd order) with each question (ie. Each successive question builds on the knowledge from the previous).
Step 1. Read the vignette and determine, from a big-picture perspective, what’s likely causing the findings. All USMLE questions follow this format and can be followed by a question of varying difficulties.
Step 2. Answer the simplest of questions first (diagnosis), then ask yourself what’s underlying these findings (ie. Is it a deficiency, pathology, etc).
Step 3. Continue with questions 2 and 3 to better understand the underlying cause(s) of the patient’s current situation.
Step 4. Review all three answers so you have a well-rounded, stronger overall picture of the concept underlying this clinical scenario.
** Aim to take this mental model into all of your USMLE practice questions **
GENERAL ANALYSIS
A 14-year-old male with decreased appetite, delayed growth, frequent infections, and delayed sexual maturity. He has a rash around his mouth, nose, eyes, hands, and feet. Laboratory findings show a decreased alkaline phosphatase. At this age, and with no prior abnormalities, we are likely dealing with a deficiency of some sort.
QUESTION 1: What condition is most likely responsible for this patient’s symptoms?
A) Perioral dermatitis
B) Acrodermatitis enteropathica
C) Atopic dermatitis
D) Marasmus
E) Kwashiorkor
Correct Answer: B) Acrodermatitis enteropathica
Explanation: The presentation of a periorificial and acral rash, poor growth, frequent infections, and low serum alkaline phosphatase are characteristic of acrodermatitis enteropathica, which results from zinc deficiency.
Incorrect Answers:
A) Perioral dermatitis: Causes a rash around the mouth but does not involve growth delay or delayed sexual maturation.
C) Atopic dermatitis: Presents as eczema but is not associated with low serum alkaline phosphatase.
D) Marasmus and E) Kwashiorkor: Are related to severe malnutrition but typically involve generalized symptoms and other distinctive signs.
QUESTION 2: What is the primary underlying cause of acrodermatitis enteropathica?
A) Vitamin A deficiency
B) Zinc absorption defect
C) Iron deficiency
D) Protein-calorie malnutrition
E) Magnesium deficiency
Correct Answer: B) Zinc absorption defect
Explanation: Acrodermatitis enteropathica is due to a genetic defect in the SLC39A4 gene, affecting zinc absorption in the intestines.
Incorrect Answers:
A) Vitamin A deficiency, C) Iron deficiency, D) Protein-calorie malnutrition, and E) Magnesium deficiency: These do not present with the specific constellation of symptoms seen here.
QUESTION #3: Which of the following laboratory findings would further support a diagnosis of acrodermatitis enteropathica?
A) Low serum zinc level
B) Elevated serum iron level
C) Low serum folate level
D) High serum ferritin level
E) Elevated serum magnesium level
Correct Answer: A) Low serum zinc level
Explanation: Low serum zinc is a hallmark finding in acrodermatitis enteropathica and confirms impaired absorption of zinc.
Incorrect Answers:
B) Elevated serum iron level, C) Low serum folate level, D) High serum ferritin level, and E) Elevated serum magnesium level: These findings are unrelated to zinc deficiency.
THE VERDICT…
Acrodermatitis enteropathica (AE) is an inherited disorder of zinc deficiency due to a genetic defect that impairs zinc absorption in the intestines. The primary cause of AE is a mutation in the SLC39A4 gene, which codes for a zinc transporter protein. This protein is essential for transporting zinc across the intestinal membrane, particularly in the duodenum and jejunum.
Zinc Deficiency Impact: Zinc is a vital trace element involved in numerous enzymatic processes, immune function, cell proliferation, and skin integrity. Deficiency disrupts these processes, leading to the characteristic symptoms of AE, such as periorificial and acral dermatitis, alopecia, and diarrhea.
Clinical Manifestations: The reduced absorption of zinc results in systemic deficiency, manifesting as scaly, erythematous skin lesions around body orifices and extremities. This can be coupled with other symptoms like alopecia and immune dysfunction, increasing susceptibility to infections.
That’s it for issue #101 of The USMLE Times!
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See ya next week 👋