<i>Pseudomonas aeruginosa</i> sepsis with sacroiliitis in X-linked agammaglobulinaemia

A boy under 5 years, with recurrent infections since 9 months of age, presented with fever and painful limping. Clinical examination revealed absent tonsils, antalgic gait and mild tenderness in the right hip joint. MRI of the pelvis demonstrated bone marrow oedema in the right sacroiliac joint, indicative of sacroiliitis. Blood cultures identified <i>Pseudomonas aeruginosa</i> as the causative organism. Immunological evaluation showed panhypogammaglobulinaemia and the absence of CD19-positive B cells in the lymphocyte subset analysis. Next-generation sequencing confirmed a hemizygous mutation (c.1256G>A variant) in the <i>BTK</i> gene at exon 14, establishing a diagnosis of X-linked agammaglobulinaemia (XLA). The child was managed with intravenous immunoglobulin and a 4-week course of antibiotics, resulting in clinical improvement. This case represents the first reported instance of <i>P. aeruginosa</i> sepsis associated with pyogenic sacroiliitis in a child with XLA, highlighting the need for vigilance in diagnosing rare infections in immunocompromised patients.