Novel Potential Treatment for Patients with Complex Regional Pain Syndrome

For patients with refractory complex regional pain syndrome (CRPS) who have exhausted all other options, inducing a coma by administering ketamine and dexmedetomidine, shows promise as a potential way to provide complete and lasting pain relief, according to research presented at the 65^th Annual Meeting of the American Academy of Neurology.

CRPS, defined as pain with continuous allodynia/hyperesthesia and autonomic dysregulation, is thought to be related to multiple factors that include central pain sensitization through the upregulation of NMDA glutamate receptors. Even for patients who receive aggressive pain management therapy, complex regional pain syndrome can be a debilitating disease. Studies have shown that ketamine, which blocks NMDA receptors, can be used at subanesthetic doses to improve overall pain scores, but that anesthetic doses are associated with better long-term pain relief. When combined with the α₂-adrenergic receptor agonist and sedative, dexmedetomidine, the analgesic effects of ketamine are synergistically enhanced, and the potential for cardiovascular side effects is reduced.

Jennifer Rasmussen, MD, of The University of Texas Health Science Center in San Antonio, and colleagues described the case report of a 45-year-old Caucasian male patient with a two-year history of pain in his left hand, resulting in allodynia, edema, and hyperhidrosis six months after the insertion of a peripheral intravenous line. The pain then spread to his entire left side, including his scrotum, rectum, and scalp.

Previous pain medications, including steroids and those for neuropathic pain and sympathetic ganglion blockade, were ineffective, and his only pain relief was achieved through the administration of 120 mg of morphine ER twice daily. The patient was treated by inducing a deep, five-day coma using ketamine (7 mg per kg per hour), dexmedetomidine (1.5 mcg per kg per hour), and midazolam (17 mg per hour). Fentanyl was given on the first day but weaned.

After emerging from his coma, the patient reported complete pain resolution and no longer needed any analgesic or opioid. Although he developed severe hallucinations and anxiety due to treatment with ketamine, chlordiazepoxide taper provided relief of this expected side effect.

The patient remained pain-free for 16 weeks and did not require any neuropathic or pain/opiate medications. After hitting his hand, the CRPS-like allodynia began again on his left side and spread within 24 hours. However, subanesthetic treatment with ketamine in the pain clinic provided complete pain resolution.

“We report the novel combination of anesthetic doses of ketamine and dexmedetomidine to treat refractory CRPS. Continued investigation into this therapy is warranted as a potential treatment regimen for CRPS,” the authors concluded.