Acute Orbital Inflammation following Neridronate Therapy: A Case Report.

Introduction: Bisphosphonates are known to occasionally induce ocular and orbital inflammation. While most reported cases involve agents such as zoledronate or alendronate, reports associated with neridronate remain exceedingly rare. Early recognition is vital as this condition can be sight-threatening but typically responds well to treatment. Case Presentation: We describe a 69-year-old man who developed fever and myalgia, followed by the abrupt onset of severe unilateral orbital inflammation 72 h after receiving an intramuscular injection of neridronic acid. Clinical examination of the left eye revealed acute visual impairment, marked eyelid edema, erythema, ptosis, proptosis, diplopia, and chemosis. Ultrasonography showed posterior scleral thickening (T-sign), while CT and MRI demonstrated diffuse orbital inflammation and intraconal fat involvement with periarterial enhancement, in the absence of infectious foci. Laboratory tests showed elevated C-reactive protein levels. Following the initiation of high-dose oral prednisone (1 mg/kg/day), the patient exhibited rapid clinical improvement within 48 h and near-complete radiologic resolution by 15 days. Conclusion: This case underscores the importance of recognizing neridronate-associated orbital inflammation as a potential adverse reaction, even following intramuscular injection. Despite its severe presentation, the condition typically demonstrates a rapid and favorable response to systemic corticosteroid therapy.