Fever of unknown origin (FUO) due to miliary BCG: The diagnostic importance of morning temperature spikes and highly elevated ferritin levels.

Fever of unknown origin (FUO) is defined as prolonged fever of >101 °F for at least 3 weeks that remains undiagnosed after a focused inpatient or outpatient workup. One of the most elusive FUO diagnoses is miliary tuberculosis (TB) which typically has few/no localizing signs/symptoms. Since the introduction of intravesicular Bacille Calmette-Guerin (BCG) treatment for bladder carcinoma, miliary BCG has only rarely been reported as a cause of FUO. As with miliary TB, there are few/no clues to suspect miliary BCG. We present an interesting case of FUO due to miliary BCG without any localizing signs, i.e., no lung, liver or prostate involvement. The only clues to the diagnosis of this FUO due to disseminated BCG were morning temperature spikes and otherwise unexplained highly elevated ferritin levels.