Acute Acalculous Cholecystitis in a Multiple Sclerosis Patient Treated with Natalizumab.

Natalizumab is a disease-modifying drug that has proved greatly effective and well-tolerated in highly-active Multiple Sclerosis (MS). However, it may increase the risk for opportunistic infections, such as viral ones. We describe a 37-year-old woman treated with Natalizumab for Relapsing-Remitting Multiple Sclerosis (RR-MS) who presented to our clinic with malaise, arthromyalgias, rash, and fever. She later developed diarrhea and severe abdominal pain. A diagnosis of parvovirus B19 (B19V) infection and acute acalculous cholecystitis (AAC) was eventually made. To our knowledge, this is the first reported case of AAC possibly related to Natalizumab therapy and B19V infection.