A 3-year-old child has recurrent bacterial infections (Streptococcus pneumoniae, Haemophilus influenzae) and diarrhoea. Flow cytometry shows absence of CD19+ B cells. Serum IgG, IgA, and IgM are all very low. The most likely diagnosis is:

• A Common variable immunodeficiency (CVID)
• B Severe combined immunodeficiency (SCID)
• C X-linked agammaglobulinaemia (Bruton disease) ✓
• D Transient hypogammaglobulinaemia of infancy

Explanation

X-linked agammaglobulinaemia (XLA, Bruton disease) presents in boys after 6 months (when maternal IgG wanes) with recurrent bacterial infections, absent B cells (CD19+), and pan-hypogammaglobulinaemia due to mutation in BTK gene causing arrest at the pro-B cell stage. CVID presents later (teens/adults), has some B cells, and has a different pattern. SCID has absent T and B cells with lymphopenia. Transient hypogammaglobulinaemia resolves spontaneously and B cells are present.

Reference: Ghai Essential Pediatrics, 10th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.