Ibrutinib as the Unifying Culprit: A Case Report of Multisystem Complications in an Elderly Patient With Low-Grade B-Cell Lymphoproliferative Disorder.

Ibrutinib, an irreversible inhibitor of Bruton's tyrosine kinase (BTK), is a cornerstone of therapy for low-grade B-cell lymphoproliferative disorders (B-cell LPD), including Waldenstrom's macroglobulinaemia (WM). While highly effective, its adverse effect profile is broad and potentially life-threatening, particularly in elderly patients with multiple comorbidities. We report an 82-year-old woman with a seven-year history of CD5-negative low-grade B-cell LPD and IgM paraproteinaemia, managed sequentially with rituximab and ibrutinib. During ibrutinib therapy, she developed a cascade of complications, including recurrent infections, platelet dysfunction, new-onset paroxysmal atrial fibrillation (AF), and haemothorax following a fall and pericardial tamponade requiring urgent pericardiocentesis. The concurrent prescription of apixaban for AF and clarithromycin for lower respiratory tract infection (LRTI) created critical drug interaction hazards. A review of her clinical course suggests that ibrutinib may have been the unifying causative agent across multiple organ systems. This case highlights the importance of vigilant monitoring for ibrutinib-associated adverse events in elderly patients, the complexity of anticoagulation decisions in the setting of ibrutinib-induced AF, and the indispensable role of multidisciplinary team (MDT) management. Clinicians should maintain a high index of suspicion for ibrutinib as the culprit when patients on this therapy develop cardiovascular, haematological, infectious, or dermatological complications.