Clinical Pearls & Morning Reports
Published February 17, 2021
Bacille Calmette–Guérin (BCG) is an attenuated live strain of Mycobacterium bovis that is most commonly administered during childhood as a vaccine to prevent tuberculosis. It is also commonly used as adjunctive therapy for the treatment of superficial bladder cancer. Read the NEJM Case Records of the Massachusetts General Hospital here.
Q: What is a “mycotic aneurysm”?
A: Some clinicians reserve the term “mycotic aneurysm” for infected aneurysms associated with endocarditis, whereas others use the term more generally for any infected aneurysm. Mycotic is a misnomer, since bacteria rather than fungi cause most mycotic aneurysms.
Q: What is currently the most common cause of infected aortic aneurysm?
A: Before the widespread use of antimicrobial therapy, syphilis was the most common cause of infected aortic aneurysm; now, staphylococcus and salmonella are the most common causes.
A: Local and systemic complications of intravesical instillation of BCG occur in less than 5% of patients who receive such treatment. In one large series, 96% of the patients with complications from BCG treatment were men, and the average age was 67 years. Mycotic aortic aneurysms developed in nearly 6% of the patients in this series. The abdominal aorta was more commonly involved than the thoracic aorta, but there can be involvement of both regions of the aorta; the iliac artery can also be involved. In most patients, systemic manifestations develop within a year after BCG treatment, but delays of nearly a decade have been reported. Disseminated BCG infection is often paucibacillary, which results in a microbiologic diagnosis based on an acid-fast bacilli smear, mycobacterial culture, or polymerase-chain-reaction–based assays being made in only 37.8% of cases.
A: Management of disseminated BCG infection consists of treatment with antituberculosis drugs and suppression of the immune response. The drug regimen typically includes rifampin, isoniazid, and ethambutol, with consideration of an agent in the fluoroquinolone drug class. Unlike tuberculosis, BCG infection is intrinsically resistant to pyrazinamide; thus, isolated pyrazinamide resistance in a mycobacterium within the M. tuberculosis complex should arouse suspicion of BCG infection. Glucocorticoids are used routinely in less severe cases of BCG infection in which the immune response is thought to be playing an important role in disease pathogenesis. Randomized, controlled trials involving patients with tuberculous meningitis have shown that the use of glucocorticoids reduces mortality. Data are lacking regarding the use of glucocorticoids in patients with central nervous system involvement associated with BCG infection; however, such treatment is thought to be beneficial. Surgical repair is often needed in cases of mycobacterial aortic aneurysms to prevent rupture.