A 6-month-old infant has Pneumocystis jirovecii pneumonia, chronic diarrhea, and oral thrush. Lymphocyte count is 800/cumm with CD4+ T cells at 150/cumm. HIV PCR is negative. Chest X-ray shows no thymic shadow. Which diagnosis is most likely?

• A X-linked agammaglobulinemia
• B DiGeorge syndrome (22q11.2 deletion)
• C Chronic granulomatous disease
• D Severe combined immunodeficiency (SCID) ✓

Explanation

SCID presents in infancy with severe opportunistic infections (Pneumocystis, candida, chronic diarrhea) due to absent T cells. The profoundly low CD4 count with opportunistic infections in an HIV-negative infant is characteristic. Absent thymic shadow supports T cell deficiency. DiGeorge syndrome shows some thymus (though hypoplastic) and less severe T cell deficiency. XLA has normal T cells. CGD presents with catalase-positive bacterial infections, not opportunistic infections.

Reference: Nelson Textbook of Pediatrics, 21st ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.