A 28-year-old man presents to the clinic with a history of recurrent sinopulmonary infections since childhood, including multiple episodes of sinusitis and pneumonia requiring antibiotics. He reports frequent episodes of watery diarrhea, particularly after consuming dairy products, and occasional urticaria after eating certain foods. He denies any history of anaphylaxis or severe systemic infections. His family history is notable for a sister with similar symptoms. Vital signs are within normal limits. Physical examination shows clear lungs and no evidence of skin rash or lymphadenopathy. Laboratory evaluation reveals undetectable immunoglobulin A levels, normal immunoglobulin G and immunoglobulin M levels, and normal B-cell and T-cell counts on flow cytometry.
C) Selective immunoglobulin A deficiency
Selective immunoglobulin A deficiency is the most common primary immunodeficiency, characterized by low or undetectable immunoglobulin A levels with normal immunoglobulin G and immunoglobulin M levels and normal lymphocyte counts. It is associated with recurrent sinopulmonary infections due to impaired mucosal immunity and gastrointestinal symptoms, such as diarrhea triggered by dairy, likely due to defective mucosal barrier function. The condition may have a genetic component, as seen with the family history in this case.
Answer choice A: Bruton agammaglobulinemia, is incorrect.Bruton agammaglobulinemia, an X-linked disorder primarily affecting males, involves absent or very low levels of all immunoglobulins due to defective B-cell maturation, leading to severe, recurrent bacterial infections starting in infancy. This is inconsistent with the isolated immunoglobulin A deficiency and normal B-cell counts in this patient.
Answer choice B: Common variable immunodeficiency, is incorrect. Common variable immunodeficiency presents with low levels of multiple immunoglobulins (immunoglobulin G, immunoglobulin A, and often immunoglobulin M) and variable B-cell defects, often accompanied by autoimmune diseases or lymphoid hyperplasia, unlike the isolated immunoglobulin A deficiency and normal immunoglobulin G and immunoglobulin M levels in this case.
Answer choice D: Severe combined immunodeficiency, is incorrect.Severe combined immunodeficiency involves defects in both B and T cells, leading to severe, life-threatening bacterial, viral, and fungal infections early in life, with low lymphocyte counts, which contrasts with the normal T-cell and B-cell counts and less severe infection profile in this patient.
Answer choice E: X-linked hyper-immunoglobulin M syndrome, is incorrect. This syndrome is characterized by elevated immunoglobulin M with low immunoglobulin G and immunoglobulin A due to defective class-switch recombination, leading to recurrent bacterial and opportunistic infections. The immunoglobulin profile does not match the isolated immunoglobulin A deficiency and normal immunoglobulin M levels in this case.
Key Learning Point
Selective immunoglobulin A deficiency is the most common primary immunodeficiency, causing recurrent sinopulmonary and gastrointestinal symptoms due to low immunoglobulin A levels, with normal immunoglobulin G, immunoglobulin M, and lymphocyte counts.
