Today’s question will test your understanding of the underlying cause of a commonly tested dermatology condition.
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A 29-year-old male presents to the clinic with a pruritic, erythematous, and edematous rash on his hands, particularly on the dorsal surface. The rash started two days ago and has been progressively worsening. The patient reports that he recently started using a new brand of dishwashing soap. His temperature is 37.0°C (98.6°F), blood pressure is 120/80 mmHg, pulse is 75/minute, and respiratory rate is 14/minute. Laboratory studies, including complete blood count, electrolytes, and renal function, are within normal limits. Which of the following best describes the underlying cause of his condition?
A. Type I hypersensitivity reaction
B. Type II hypersensitivity reaction
C. Type III hypersensitivity reaction
D. Type IV hypersensitivity reaction
E. Neutrophilic infiltration and activation
F. Complement-mediated cell lysis
G. Immune complex deposition
Detailed Breakdown of Answers + Correct Answer Below ⏬
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 skills). Here’s how to think through this question:
Step 1. Read the last line to get to the heart of the question: “Which of the following best describes the underlying cause of his condition?”
Step 2: Is this a first-, second-, or third-order question?
Answer: 2nd order. 1st: Diagnose the condition, and 2nd: Identify the underlying cause of the condition.
Step 3: Read the vignette carefully and ask yourself: “Based on my diagnosis, what’s the most likely underlying cause?”
Step 4. Look at the answer choices and select the option most closely resembling your final thought from “Step 3” above.
GENERAL ANALYSIS
The clinical presentation of the 29-year-old male with a pruritic, erythematous, and edematous rash on his hands, particularly after using a new brand of dishwashing soap, is indicative of contact dermatitis.
ANSWER CHOICES:
CHOICE A: Type I hypersensitivity reaction
Explanation: Type I hypersensitivity reactions are immediate allergic reactions mediated by IgE antibodies. They typically occur within minutes to hours and include conditions like anaphylaxis and allergic rhinitis. The delayed onset and contact nature of the rash suggest a different mechanism.
CHOICE B: Type II hypersensitivity reaction
Explanation: Type II reactions involve IgG or IgM antibodies directed against cell surface or matrix antigens, leading to cytotoxic effects. Examples include hemolytic anemia and Goodpasture syndrome. This mechanism does not align with the presentation of contact dermatitis.
CHOICE C: Type III hypersensitivity reaction
Explanation: Type III reactions are mediated by immune complexes that deposit in tissues, causing inflammation. Conditions include systemic lupus erythematosus and serum sickness. The patient's symptoms do not involve immune complex deposition.
CHOICE D: Type IV hypersensitivity reaction
Explanation: Type IV reactions are delayed-type hypersensitivity reactions mediated by T cells. They occur 48–72 hours after exposure and include conditions like contact dermatitis and tuberculin skin tests. The patient's symptoms and timing are consistent with a Type IV hypersensitivity reaction caused by contact with an allergen in the dishwashing soap.
CHOICE E: Neutrophilic infiltration and activation
Explanation: Neutrophilic infiltration is common in acute bacterial infections and inflammatory responses but is not specific to hypersensitivity reactions.
CHOICE F: Complement-mediated cell lysis
Explanation: This mechanism is associated with Type II hypersensitivity reactions where complement activation leads to cell lysis.
CHOICE G: Immune complex deposition
Explanation: This describes type III hypersensitivity reactions where immune complexes deposit in tissues, causing inflammation. The clinical scenario does not involve immune complex deposition.
FINAL VERDICT…
The patient's symptoms are consistent with contact dermatitis, a classic example of a Type IV hypersensitivity reaction. This type of reaction is mediated by T cells and occurs after exposure to an allergen, such as chemicals in dishwashing soap, leading to a delayed inflammatory response.
CORRECT ANSWER: D) Type IV hypersensitivity reaction
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That’s it for question 82!
See ya next time 👋