A boy presents at 6 months with severe bacterial and fungal infections. Lymph nodes are absent. Serum immunoglobulins are undetectable. Peripheral blood shows no B cells and no T cells. The most likely diagnosis is:

• A X-linked agammaglobulinemia (Bruton's disease)
• B DiGeorge syndrome
• C Common variable immunodeficiency
• D Severe combined immunodeficiency (SCID) ✓

Explanation

SCID presents in infancy with combined absence of T cells and B cells, making patients susceptible to bacteria, viruses, fungi, and Pneumocystis. Absent thymic shadow and absent lymphoid tissue are additional features. Bruton's agammaglobulinemia has absent B cells but normal T cells; DiGeorge syndrome primarily affects T cells due to thymic aplasia; CVID presents in adulthood with hypogammaglobulinemia but normal B-cell numbers.

Reference: Robbins & Cotran Pathologic Basis of Disease, 10th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.