Novel Association Between Intrathecal Drug Administration and Arachnoiditis Ossificans

BACKGROUND: We present a case of delayed progression of adhesive arachnoiditis to arachnoiditis ossificans (AO) in a patient being treated with a high-dose polypharmaceutical intrathecal regimen. CASE DESCRIPTION: The patient is a 39-year-old Caucasian male who was implanted with an intrathecal pump in 2006 to control severe low back pain and administered intrathecal pain medication for a period of 10 years. In 2016, he developed new-onset radicular pain and worsened sensation in his lower extremities. Computed tomography scan of the lumbar spine at that time demonstrated profound calcification of the arachnoid consistent with a diagnosis of AO. It was presumed that prolonged high-dose intrathecal medication precipitated this condition, and his intrathecal medications were titrated down with removal of the pump. CONCLUSIONS: It is unlikely that his condition occurred as a result of prior surgery, with the more likely cause being hyperplasia of the spinal arachnoid, leading to scarring and calcification, due to the high-dose intrathecal regimen. This case highlights the delayed progression from stable arachnoiditis to AO concurring with a regimen of high-dose intrathecal medications. Clinicians should closely monitor patients undergoing intrathecal drug administration, particularly at elevated doses, for indications of damage to the spinal arachnoid mater.