A 6-month-old boy is brought to the clinic for evaluation of recurrent infections since birth, including persistent oral thrush, pneumocystis pneumonia, and a recent episode of bacterial otitis media. His mother reports frequent diaper rashes and failure to thrive. His heart rate is 120 beats/minute, and his blood pressure is 80/60 mmHg. Physical examination reveals a small thymus on chest imaging, absent tonsils, and no palpable lymph nodes. Laboratory evaluation shows markedly reduced T-cell counts, normal B-cell counts, and low immunoglobulin G, immunoglobulin A, and immunoglobulin M levels.
Which of the following is the most likely diagnosis?
The correct answer is:
A) DiGeorge syndrome
DiGeorge syndrome (22q11.2 deletion) is characterized by thymic hypoplasia, leading to T-cell deficiency, which predisposes to recurrent viral, fungal, and opportunistic infections such as pneumocystis pneumonia and oral thrush. Low immunoglobulin levels result from impaired T-cell help for B-cell antibody production. The small thymus, absent tonsils, and lack of lymph nodes support this diagnosis.
Answer choice B: Hyper-immunoglobulin E syndrome, is incorrect. Hyper-immunoglobulin E syndrome (Job syndrome) features elevated immunoglobulin E levels, recurrent skin and lung infections, eczema, and eosinophilia, with normal or elevated T-cell counts.
Answer choice C: Selective immunoglobulin A deficiency, is incorrect. Selective immunoglobulin A deficiency involves isolated low immunoglobulin A levels with normal T-cell counts and typically milder sinopulmonary infections, not the severe opportunistic infections or T-cell deficiency seen here.
Answer choice D: Wiskott-Aldrich syndrome, is incorrect. Wiskott-Aldrich syndrome presents with eczema, thrombocytopenia, and recurrent infections due to combined B- and T-cell defects, but T-cell counts are not as severely reduced. Thrombocytopenia is not mentioned in this vignette.
Answer choice E: X-linked agammaglobulinemia, is incorrect. X-linked agammaglobulinemia causes low levels of all immunoglobulins due to absent B cells, leading to recurrent bacterial infections. T-cell counts are normal, and opportunistic infections like pneumocystis pneumonia are less common.
Key Learning Point
DiGeorge syndrome, caused by 22q11.2 deletion, leads to T-cell deficiency due to thymic hypoplasia, resulting in recurrent viral, fungal, and opportunistic infections, low immunoglobulin levels, and physical findings such as absent thymus and tonsils.
