Background: Bacillus Calmette-Guerin (BCG) bladder instillations have been long known to successfully treat non-muscle invasive bladder cancer. The objective of this report is to highlight the first case to our knowledge of Varicella Zoster virus (VZV) shingles reactivation to BCG. Case presentation: An 80-year-old male with history of Parkinson’s disease and recurring high-grade T1 bladder cancer. Five days after first repeat BCG instillation, patient presented to the emergency room with a progressively worsening rash that started 1 day after treatment, characterized as VZV shingles reactivation. Intravenous acyclovir treatment produced rapid clinical improvement. Conclusion: Reactivation of dormant VZV infection may be a reaction to BCG intravesical instillation. This is, to the authors’ knowledge, the first documented case of this complication. Although coincidence cannot be completely ruled out, the timing of this case and the context of immunosuppression-immunomodulation inherent to BCG therapy make causality plausible.

Keywords: BCG, shingles, bladder cancer, adverse reaction, varicella zoster, case report