#74 - THE WEEKLY USMLE TIMES
Highlights for the week of May 6, 2024
Welcome to issue #74 of The USMLE Times… A special welcome to the 99 new members who have joined our community this week.
Here’s what’s on tap for issue #74 of the USMLE Times:
Question of the Week
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Question deep-dive & breakdown
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Let’s dive in!
A 7-year-old female is being evaluated for recurring respiratory infections for the past two years. She was breastfed exclusively until six months of age, during which no illnesses occurred. Her vital signs include temperature of 99.1°F, blood pressure of 105/70 mmHg, pulse of 90/minute, and respiratory rate of 14/minute. Physical examination demonstrates sinus pain when pressure is applied, while the rest of the examination is unremarkable. Further inquiry into the patient's medical history reveals a past diagnosis of atopy. Given the clinical presentation, selective IgA deficiency is suspected. Which of the following findings would be expected upon confirmation of this diagnosis?
A. Normal IgG and IgM levels
B. Low levels of IgM and IgA, with normal IgG
C. Subsets of normal B and T cells on flow cytometry
D. Absent B cells on flow cytometry
E. Absent lymphoid tissue
The answer & question breakdown is at the bottom of the post.
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ANSWER + QUESTION BREAKDOWN
This question revolves around diagnosing a common immunodeficiency disorder in a young child presenting with recurrent respiratory infections. With suspicion of a selective IgA deficiency, we should proceed through the answer choices with that in mind. Correctly answering this question requires a detailed understanding of immunoglobulin function, especially the roles and distribution of various immunoglobulin types (IgG, IgM, IgA). Furthermore, the question assesses your knowledge of the diagnostic approach for immunodeficiency, including immunoglobulin testing and flow cytometry analysis.
ANSWER CHOICES:
ANSWER CHOICE A: Normal IgG and IgM levels
Selective IgA deficiency is characterized by a lack of IgA production, while other immunoglobulins—namely IgG and IgM—remain within the normal range. This option is plausible as it suggests the presence of normal IgG and IgM levels, which aligns with the typical profile of selective IgA deficiency.
ANSWER CHOICE B: Low levels of IgM and IgA, with normal IgG
This answer choice suggests a combined immunodeficiency affecting IgM and IgA production, which is inconsistent with selective IgA deficiency. Only IgA levels are affected in selective IgA deficiency, while IgM and IgG levels remain normal.
ANSWER CHOICE C: Subsets of normal B and T cells on flow cytometry
In selective IgA deficiency, the number and function of B and T cells are generally normal. Flow cytometry would reveal normal subsets of these lymphocytes, making this answer choice consistent with the expected findings.
ANSWER CHOICE D: Absent B cells on flow cytometry
Absent B cells on flow cytometry suggest a more severe immunodeficiency, such as X-linked agammaglobulinemia, rather than selective IgA deficiency. B cells are present in selective IgA deficiency but fail to produce IgA.
ANSWER CHOICE E: Absent lymphoid tissue
Absent lymphoid tissue can be seen in conditions like severe combined immunodeficiency (SCID), where cellular and humoral immunity is compromised. This is much more severe than selective IgA deficiency and does not match the patient's mild clinical presentation.
THE VERDICT: In selective IgA deficiency, the primary immunological abnormality is a significant reduction or absence of IgA levels in serum and secretions. This deficiency results from the inability of B cells to differentiate into IgA-secreting plasma cells despite the presence of normal numbers of B cells and other immunoglobulin isotypes.
Patients with selective IgA deficiency typically have normal levels of IgG and IgM, as their B cells can still differentiate into plasma cells that secrete these immunoglobulins. Flow cytometry would reveal normal subsets of B and T cells, as the defect lies in the differentiation process rather than the presence or absence of these lymphocytes.
The recurring respiratory infections in this patient can be attributed to the lack of secretory IgA in the mucous membranes of the respiratory tract, which compromises local immune defenses against pathogens.
In summary, the presence of normal IgG and IgM levels, along with the clinical presentation and history, strongly supports the diagnosis of selective IgA deficiency in this patient.
FINAL ANSWER: A: Normal IgG and IgM levels
That’s it for issue #74 of The USMLE Times!
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