USMLE · Question #581
USMLE Question #581: Real Exam Question with Answer & Explanation
The correct answer is A. absence of type IV hypersensitivity. This patient most likely has thymic aplasia which is also known as DiGeorge syndrome. It is caused by a 22q11 deletion and failure of the 3 and 4 pharyngeal rd th pouches to develop which leads to the absence of the thymus and parathyroid glands. Patients may present with tetany,
Question
Options
- Aabsence of type IV hypersensitivity
- Bdecreased alpha fetoprotein
- Celevated IgE levels
- Delevated IgM levels
- Eprominent telangiectasias around the eyes
Explanation
This patient most likely has thymic aplasia which is also known as DiGeorge syndrome. It is caused by a 22q11 deletion and failure of the 3 and 4 pharyngeal rd th pouches to develop which leads to the absence of the thymus and parathyroid glands. Patients may present with tetany, usually seen in the facial muscles, due to hypocalcemia secondary to hypoparathyroidism. Recurrent infections due to defective cellular immunity and abnormal facies are due to decreased levels of T cells since patients without a thymus are unable to complete normal T-lymphocyte development. Type IV hypersensitivity which is totally dependent on T lymphocytes is absent in these patients. Other findings include tetralogy of Fallot and truncus arteriosus.
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