Mycotic Aneurysm of the Ulnar Artery Secondary to Bacillus Calmette-Guérin Therapy for Bladder Cancer: A Rare Presentation of Hypothenar Hammer Syndrome

Mycotic aneurysms, especially those of the upper extremity, are rarely reported in literature. These aneurysms are caused by bacterial endocarditis and, therefore, are more commonly seen in patients who are in an immunocompromised state, including those requiring bacillus Calmette-Guérin (BCG) therapy for bladder cancer. Owing to the inevitable rupture of mycotic aneurysms, the standard treatment is surgical repair with appropriate secondary antibiotics. We present a unique case of a mycotic ulnar artery aneurysm following BCG therapy and repetitive hand trauma in a patient with bladder cancer that was successfully repaired with microsurgical techniques and secondary antibiotics.