Dissociative Mental State in a Patient with an Intrathecal Drug Administration System

Abstract

A dvances in technology for long-term intrathecal drug administration, along with evolving knowledge about the neurophysiology and pharmacology of spinal nociception, have created a new option for enhanced analgesia for patients suffering from chronic pain. As noted in a review involving 13,342 mainly US-based chronic pain patients, the use of long-term infusions of intrathecal medications has significantly increased (1). Intrathecal drug administration is cost-effective when compared with other analgesic modalities for patients with failed back surgery syndrome (2). The practice of using drugs other than morphine is also increasing despite little data on long-term safety of such adjuvant therapy.Neuraxial administration of opioids can cause central nervous system (CNS) excitation, which can manifest as delirium or agitation (3). Significant neural toxicity can occur if inappropriate medications are infused intrathecally via an implanted reservoir. In evaluating patients who present with neuropsychiatric disorders and who have a spinal catheter in situ, the supraspinal effects of intrathecal infusions should be considered. We describe a patient who developed an acute dissociative mental state, which resolved on removal of intrathecal medication from his pump reservoir. Toxicology analysis revealed that the injectate was falsely positive for phencyclidine and methadone. Case ReportA 55-yr-old man suffering from chronic back and left leg pain was referred to the pain management center for consideration of a trial of intrathecal opiates. He had undergone numerous interventional pain management techniques at other centers over the previous 10 yr, including a trial of dorsal column stimulation, and was knowledgeable about sophisticated modalities of pain control. His intake of medications included 75-85 mg/d of oxycodone. His medical history was significant for previous lumbar discectomy, depression, and gastric bypass surgery.After psychological evaluation, the patient underwent a trial of intrathecal opioid administration that resulted in significant pain reduction and was subsequently implanted with a Medtronic Synchromed ® (Medtronic, Minneapolis, MN) intrathecal pump. Tolerance to intrathecal morphine developed rapidly, requiring progressive increases in the daily dose from 2 mg/d immediately after implantation to 13.8 mg/d 6 mo later. The infusion comprised of a complexcontinuous pattern involving several dosage adjustments daily. During this time, the patient experienced no apparent mental status changes despite escalating intrathecal opioid doses and continuation of oral opioids.Approximately 7 mo after the initiation of intrathecal therapy, the patient exhibited cognitive deterioration, presenting to the emergency room in a dissociative mental state. This had developed acutely over the previous 3 days and featured stammering speech, mild lethargy, blunting of affect, and both long-and short-term memory loss. There was no history of head trauma, and no definitive injuries were identified. The cognitive deficit...