Multisystemic Processes (USMLE Step 1 Question)
USMLE Step 1 Practice Question
Today’s question will test your knowledge of an often-tested, high-yield USMLE Step 1 concept. The question is followed by a breakdown of the answer choices and a detailed explanation of the correct answer. Good luck!
A 24-year-old male presents to the clinic with a two-week history of joint pain and swelling in his knees and ankles. He reports that his symptoms began after experiencing diarrhea and abdominal cramping following a meal at a new restaurant. On physical examination, there is conjunctival injection, and the patient also mentions occasional eye pain and blurry vision. Laboratory tests reveal elevated erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) levels. Which of the following is the most likely underlying cause of this patient's symptoms?
A) Activation of autoreactive T cells against self-antigens
B) Formation of neutrophil extracellular traps in the joints
C) Immune complex deposition leading to complement activation
D) Molecular mimicry leading to cross-reactivity with self-antigens
E) Inappropriate activation of the inflammasome and IL-1β release
Scroll down for the breakdown ⏬
ANSWER + QUESTION BREAKDOWN
The Mental Model for this week’s question:
Step 1. Identify the goal of the question (ID the underlying cause).
Step 2. Make a diagnosis.
Step 3. Ask yourself what underlying process is causing the problem.
Step 4. Look for your answer in the answer choices.
GENERAL ANALYSIS
This patient presents with a classic triad of symptoms: arthritis, conjunctivitis, and a recent history of gastrointestinal infection, which are highly suggestive of reactive arthritis (ReA). Reactive arthritis is a type of spondyloarthropathy that typically occurs after an infection, most commonly gastrointestinal or genitourinary. The elevated ESR and CRP levels indicate an inflammatory process. The key to diagnosing reactive arthritis is the temporal relationship between the infection and the onset of arthritis, along with the presence of extra-articular manifestations such as conjunctivitis.
ANSWER CHOICES:
ANSWER CHOICE A: Activation of autoreactive T cells against self-antigens
This mechanism is characteristic of autoimmune diseases such as multiple sclerosis or type 1 diabetes, where T cells target the body's own tissues. This is not the primary mechanism in reactive arthritis.
ANSWER CHOICE B: Formation of neutrophil extracellular traps in the joints
Neutrophil extracellular traps (NETs) are involved in the pathogenesis of conditions like SLE and some forms of vasculitis. While neutrophils play a role in inflammation, this is not the main mechanism in reactive arthritis.
ANSWER CHOICE C: Immune complex deposition leading to complement activation
Immune complex deposition is a key feature of diseases like systemic lupus erythematosus (SLE) and post-streptococcal glomerulonephritis. It is not the primary mechanism in reactive arthritis.
ANSWER CHOICE D: Molecular mimicry leading to cross-reactivity with self-antigens
An immune response to infection can cross-react with self-antigens due to molecular mimicry. This leads to an autoimmune reaction against joint tissues and other organs.
ANSWER CHOICE E: Inappropriate activation of the inflammasome and IL-1β release
This mechanism is characteristic of autoinflammatory diseases such as rheumatoid arthritis.
FINAL VERDICT…
Reactive arthritis is triggered by an infection, often gastrointestinal or genitourinary, and is thought to involve molecular mimicry. In this process, antigens from the infectious agent resemble self-antigens, leading to an autoimmune response where the immune system attacks the body's own tissues, including the joints, eyes, and other organs. This explains the patient's joint pain, conjunctivitis, and the temporal relationship with a recent gastrointestinal infection. The elevated ESR and CRP levels further support an inflammatory process consistent with reactive arthritis.
FINAL ANSWER: D: Molecular mimicry leading to cross-reactivity with self-antigens
That’s it for today’s question!
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A nice question ✨🤍