If you’re preparing for the United States Medical Licensing Examination® (USMLE®) Step 1 exam, you might want to know which questions are most often missed by test-prep takers. Check out this example from Kaplan Medical, and read an expert explanation of the answer. Also check out all posts in this series.
This month’s stumper
A 17-year-old boy is preparing for elective surgery. During his preoperative work-up, it is discovered that he has had recurrent lung infections, otitis media and sinusitis for most of his life. He is referred to a specialist for further evaluation. Laboratory studies show the following:
Ig isotype - Patient’s value (mg/dL)
IgM – 160
IgG – 770
IgA – 4
Which of the following additional finding is most likely to be seen in this patient?
A. Contact dermatitis.
B. Decreased phagocyte efficiency.
C. Immune complex disease.
D. Increased atopy.
E. Partial albinism.
The correct answer is D.
Kaplan Medical explains why
This patient has selective IgA deficiency. The serum values quoted in this case are normal for all isotypes except IgA, which is significantly depressed.
- Selective IgA deficiency is the most common immunodeficiency disease in the United States.
- Patients have a tendency toward recurrent pulmonary and upper respiratory infections as well as atopic allergy.
- Patients can also present with infectious diarrheas.
- These patients seem to isotype switch to IgE more frequently because of their inability to produce IgA. It is important to note that many patients with selective IgA deficiency have anti-IgA IgE antibodies. As such, they may have severe allergic reactions to blood products. Interestingly, these patients can receive blood products safely from other IgA-deficient donors.
Why the other answers are wrong
Choice A: Contact dermatitis is a type of delayed-type hypersensitivity that depends on TH1 cells, macrophages, and cytotoxic T lymphocytes. It is not increased in patients with selective IgA deficiency.
Choice B: Decreased phagocytic efficiency is the hallmark of chronic granulomatous disease, but it is not often associated with changes in immunoglobulin.
Choice C: Immune complex disease is more common in patients with complement deficiency. C3b plays an important role in the clearing of immune complexes (antigen-antibody) from the serum. It would not be associated with selective IgA deficiency.
Choice E: Partial albinism is found in Chédiak-Higashi syndrome, which is a defect in phagolysosome fusion within phagocytic cells. IgA is normal.
Tips to remember
Selective IgA deficiency:
- Increased susceptibility to mucosal pathogens.
- Increased incidence of atopic allergy (high IgE).
- Increased risk for transfusion reactions.
For more prep questions on USMLE Steps 1, 2 and 3, view other posts in this series.
The AMA and Kaplan have teamed up to support you in reaching your goal of passing the USMLE® or COMLEX-USA®. If you're looking for additional resources, Kaplan provides free access to tools for pre-clinical studies, including Kaplan’s Lecture Notes series, Integrated Vignettes, Shelf Prep and more.
