Case Presentation: A 91-year-old Japanese man was referred to our institution for the management of a ruptured thoracic aortic aneurysm. Two days prior, he had been admitted to another hospital with a one-week history of fever. Chest computed tomography (CT) revealed fluid accumulation around the descending aorta and a left pleural effusion, which was bloody, suggestive of a ruptured mycotic aortic aneurysm. Consequently, the patient was referred to our facility. His past medical history included bladder cancer, diagnosed two years earlier, which had been treated with transurethral resection followed by seven sessions of intravesical instillation of Mycobacterium bovis Bacillus Calmette-Guérin (BCG). On examination, his temperature was 37.7°C, blood pressure 139/88 mmHg, heart rate 90 beats per minute. Auscultation revealed diminished breath sounds on the left. Laboratory tests showed a white blood cell count of 7,900/μL, hemoglobin 7.2 g/dL, platelets 252,000/μL, and C-reactive protein 15.2 mg/dL. Contrast-enhanced chest CT demonstrated saccular outpouchings with encapsulated fluid around the descending aorta. Due to his advanced age, aneurysmal resection was deemed excessively hazardous; consequently, the patient underwent emergent thoracic endovascular aortic repair. On hospital day 5, pleural fluid acid-fast smear was negative, but polymerase chain reaction (PCR) for Mycobacterium tuberculosis was positive, later identified as Mycobacterium bovis via multiplex PCR. Blood cultures for both bacteria and acid-fast bacilli were negative. On hospital day 7, thoracoscopy under local anesthesia revealed white pleural thickening, and cultures from this site tested positive for M. bovis. The patient was diagnosed with a ruptured mycotic aneurysm and secondary pleuritis caused by M. bovis. He was treated with isoniazid (5 mg/kg daily, orally), rifampin (10 mg/kg daily, orally), and ethambutol (15 mg/kg every other day, orally), which led to symptom resolution. The patient was discharged on hospital day 15.
Discussion: Intravesical BCG therapy is a cornerstone of adjunctive treatment for non-muscle invasive urothelial carcinoma of the bladder. Although generally safe, intravesical BCG therapy can cause localized adverse reactions, such as flu-like symptoms, with serious systemic complications reported in fewer than 5% of cases. Mycotic aneurysms, often caused by Staphylococcus aureus or Salmonella enterica, are rarely associated with M. bovis following intravesical BCG therapy. The nonspecific nature of mycotic aneurysm symptoms frequently delays diagnosis. In this case, pleurisy was confirmed via thoracoscopy under local anesthesia, and the infection likely resulted from direct bacterial invasion into the pleural cavity following aneurysmal rupture. There is no established treatment protocol for M. bovis-related mycotic aneurysms; however, surgical intervention coupled with antimycobacterial therapy is often necessary, with a reported mortality rate of approximately 19%. This case underscores the critical need for prompt multidisciplinary collaboration among hospitalists, infectious disease specialists, cardiovascular surgeons, and thoracic surgeons.
Conclusions: We report a case of a mycotic aneurysm and pleurisy caused by M. bovis infection following intravesical BCG therapy. This case highlights the importance of maintaining a high index of suspicion for BCG-related systemic disease in patients presenting with fever after undergoing BCG therapy.