Diverticular Perforation with Normal C-reactive Protein in a Patient with Neuromyelitis Optica Spectrum Disorder Receiving Satralizumab.

Interleukin-6 blockade can blunt inflammatory biomarkers and mask serious infection. A 49-year-old woman with neuromyelitis optica spectrum disorder receiving satralizumab presented with mild abdominal pain; C-reactive protein levels were normal at the time of perforation despite a transient elevation early during hospitalization. Computed tomography revealed colonic diverticular perforation with a localized abscess. She improved with percutaneous drainage, targeted antimicrobials, and withdrawal of satralizumab, followed by transition to ravulizumab. This case suggests that satralizumab may obscure inflammatory responses, delaying recognition of gastrointestinal perforation. Normal C-reactive protein levels do not exclude complicated diverticulitis during interleukin-6 receptor blockade; early imaging and a low threshold for intervention are essential.