Prolonged ketamine infusion as a therapy for complex regional pain syndrome: synergism with antagonism?

Abstract

Complex regional pain syndrome (CRPS) remains a troubling and often refractory pain condition that typically develops either following injury to a peripheral nerve (type II) or following trauma without obvious peripheral nerve damage (type I). It presents with a characteristic constellation of sensory, motor, autonomic and vascular signs, within which pain is the central feature. Its aetiology is uncertain [1], and there is an ongoing debate about whether it is primarily a neuropathic or an inflammatory/autoimmune condition [2]. The existing data from treatment trials of conventional analgesics, antineuropathic pain medications or nerve blocks have been largely disappointing [3,4], and much of the emphasis in treatment is on functional rehabilitation (see the recent Royal College of Physicians treatment guidelines [5]). The limitations of existing treatments means that a substantial cohort of CRPS patients (∼15 000 new cases per year in the UK based on the incidence figures of de Mos et al. [6]) is left with refractory, long-term severe pain causing significant disability. Consequently, there is a need to develop innovative treatment approaches, such as graded motor imagery, mirror visual feedback, spinal cord stimulation and transcranial magnetic stimulation, all of which have shown some utility in clinical trials. Set within this context, the review of Niesters et al. [7] in this issue of BJCP is timely, and articulates the arguments for a role of prolonged ketamine infusion in the management of neuropathic pain and specifically for CRPS.