853 - Intravenous Ketamine as an Effective Treatment Modality for Phantom Limb Pain

Case Diagnosis: Phantom Limb Pain

Case Description: A 59-year-old female with a history of depression, hypothyroidism, right knee arthroplasty previously complicated by chronic periprosthetic joint infections, and an intrathecal hydromorphone pump (placed in 2021, dispensing 7.587 mg of hydromorphone daily) presented to the hospital for a right above-knee amputation. She reported 10/10 pain prior to admission which changed post-operatively, endorsing new burning and stabbing pain at the non-existing portion of her previous lower limb, alongside a new pins and needles sensation at the residual limb. Physical examination highlighted hyperalgesia at the residual limb. With opioid administration already in place via intrathecal pump, she was started on 0.1mg/kg per hour of intravenous ketamine. Subsequently, she tolerated bedside physical therapy and subjectively reported decreased pain from the residual limb and the site of her previous non-existent limb. The following day, she reported 5/10 pain, with dramatic improvements in functional status.

Discussions: Phantom limb pain affects approximately 80% of limb-loss or limb-discrepancy patients. Early animal and human studies suggest hyperexcitability and sensitization of NMDA receptors may be central to the pathophysiology of this neuropathic condition. Therefore, it is possible NMDA antagonists can offer efficacious management of acute or chronic phantom limb pain. In this case, the patient experienced postoperative pain at the residual limb and non-existent previous limb that was consistent with acute residual limb pain and phantom limb pain. Pain remained uncontrolled even while on high doses of hydromorphone via intrathecal pump. Low-dose ketamine was found to show objective and subjective improvements in pain and objective therapy scores, with eventual resolution of her phantom limb pain.

Conclusions: Low dose intravenous ketamine provides a potentially effective treatment option for acute phantom limb pain.