What CRPS actually is — Type 1 vs. Type 2

Complex regional pain syndrome (CRPS) is a chronic pain condition that usually develops in a single limb after an injury, surgery, or sometimes a relatively minor event. The pain is typically out of proportion to the inciting trauma, and it is accompanied by changes in skin color and temperature, swelling, sweating abnormalities, and motor dysfunction in the affected limb. Many patients describe burning, electric, or crushing pain that does not respond predictably to the usual analgesic ladder.

CRPS is divided into two types. Type 1 (formerly called reflex sympathetic dystrophy, or RSD) develops without identifiable nerve injury. Type 2 (formerly causalgia) follows a confirmed nerve injury. The mechanisms overlap, and the treatment approaches are similar, but the distinction matters for diagnosis and disability documentation.

What sets CRPS apart from many other chronic pain conditions is how aggressively it can progress when untreated. Limbs can become functionally useless. The nervous system reorganizes around the pain in ways that become harder to reverse over time. This is why specialists often talk about a treatment window: earlier intervention tends to produce better outcomes than waiting until the syndrome has been entrenched for years.

Ketamine is FDA-approved as an anesthetic; its use for CRPS is off-label. That said, CRPS has more dedicated randomized controlled trial data behind it than nearly any other off-label ketamine indication, which is why it sits in a different category than many newer ketamine applications.

Why ketamine targets the pain mechanism

The pain in CRPS is not generated solely by ongoing tissue damage. It is sustained by changes in the central nervous system — particularly at the level of the spinal cord and brain — that amplify and perpetuate pain signals long after the initial injury has healed. This phenomenon is called central sensitization, and it is driven in large part by the NMDA receptor, a glutamate-gated channel that controls how the nervous system encodes painful input.

In CRPS, NMDA receptors in the dorsal horn of the spinal cord become overactive. They produce a state called “wind-up,” in which each successive pain signal lands harder than the last. Touch becomes burning. Light pressure becomes crushing. The nervous system has effectively been rewired around the injury.

Ketamine is a non-competitive NMDA receptor antagonist. By blocking the channel, it can interrupt the wind-up cascade and, in many patients, allow the central pain machinery to recalibrate toward a less hyperexcitable state. This is the same mechanism that underlies its effects on other central-sensitization conditions, including fibromyalgia and broader categories of chronic neuropathic pain. CRPS just happens to be the condition where the trial evidence is most direct.

Sigtermans 2009: the 4.2-day infusion trial

The benchmark study in this space is the trial by Sigtermans and colleagues, published in Pain in 2009. It is a randomized, double-blind, placebo-controlled trial of 60 patients with CRPS Type 1. Participants received either continuous IV ketamine or placebo over an average of 4.2 days, with doses titrated upward based on tolerability and side effects.

The results were notable. Patients in the ketamine arm reported significant pain reduction compared with placebo, and the effect did not disappear when the infusion ended. Pain scores remained meaningfully lower than placebo at multiple follow-up points, including week four and week eight. By week twelve the difference between groups had narrowed and statistical significance attenuated, but the trajectory still favored the ketamine arm.

Two things made this trial structurally important. First, it was randomized and placebo-controlled in a chronic pain population where placebo arms are notoriously difficult to construct. Second, it demonstrated that the analgesic effect of a multi-day ketamine infusion can outlast the infusion itself by weeks — a finding consistent with the idea that ketamine is doing something to the underlying central sensitization rather than simply masking pain.

Sigtermans is not without limitations. The protocol used relatively high cumulative doses, which raises questions about translating it to outpatient settings. Functional outcomes were less robust than pain outcomes. And not every patient responded. But as a proof-of-concept that ketamine can change the trajectory of CRPS, the trial remains the cornerstone reference.

Schwartzman 2009: outpatient repeated dosing

Published in the same year and the same journal, Schwartzman and colleagues ran a different design that is arguably more relevant to how ketamine is delivered today. Their Pain 2009 trial used a placebo-controlled protocol of repeated outpatient IV ketamine infusions over a 10-day period in patients with CRPS.

The Schwartzman group reported significant reductions in pain in the ketamine arm relative to placebo, along with measurable improvements in motor function and autonomic features such as skin temperature regulation and color change. This is meaningful because CRPS is not a pure pain syndrome — it is a multi-system disorder, and a treatment that helps only the pain dimension while leaving motor and autonomic symptoms untouched is doing less than it could.

Together, Sigtermans and Schwartzman bracket the question of how to deliver ketamine for CRPS. Sigtermans showed what a longer, higher-intensity inpatient-style infusion can do. Schwartzman showed that a more modest outpatient series can also produce real results. Most modern outpatient ketamine clinics, including ours, draw protocol elements from the Schwartzman side of the literature.

Where the durability question stands

One of the most important and unresolved questions in CRPS ketamine research is how long the benefit lasts. The trials disagree on specifics, but the broad picture is that relief lasts weeks to a few months for many responders, with a subset enjoying longer-duration improvement and another subset relapsing within weeks.

A 2014 review by Niesters and colleagues in the British Journal of Clinical Pharmacology synthesized data from multiple prolonged-infusion studies and concluded that ketamine infusions lasting 4 to 14 days have produced analgesic effects extending up to roughly three months post-infusion in some patients. The review was careful to note variability: protocols, dosing, and patient selection all shifted the durability picture meaningfully.

The Reflex Sympathetic Dystrophy Syndrome Association (RSDSA), the leading patient-advocacy and clinical-resource organization for CRPS, recognizes ketamine infusion as one of the more promising treatments for refractory CRPS. Their clinical resources emphasize the same caveats the trial literature does: protocols vary widely, durability is patient-dependent, and specialist oversight matters because CRPS patients often have complex medication regimens and comorbidities.

Practically, this means many CRPS patients on ketamine therapy plan for the possibility of booster infusions. A response that lasts six weeks is still useful if a maintenance schedule can extend that response across the year. Research suggests that maintenance dosing can preserve benefit for a meaningful subset of responders, though optimal scheduling remains an open question.

Risks and side effects in the CRPS population

Ketamine is well-characterized after more than fifty years of clinical use, and the side-effect profile in CRPS trials has been broadly consistent with its profile in other infusion contexts. Acute side effects during the infusion can include dissociation, mild confusion, blurred vision, mild sedation, nausea, and transient elevations in blood pressure and heart rate. Most resolve within minutes of the infusion ending.

For CRPS patients specifically, two factors deserve emphasis. First, many CRPS patients are taking multiple concurrent medications — gabapentinoids, antidepressants, benzodiazepines, opioids, topical agents — and interaction profiles need to be reviewed in advance. We coordinate with prescribing physicians rather than asking patients to navigate this themselves. Second, longer or higher-dose protocols have been associated, in some long-term frequent-use contexts, with bladder and hepatic concerns. Standard intermittent infusion therapy is not the same risk profile as recreational chronic use, but it is still something specialists track.

At Music City Ketamine, Marla Peterson, CRNA, oversees every infusion with anesthesia-level monitoring — continuous pulse oximetry, blood pressure, and heart rate tracking, with the CRNA in the room and available throughout. CRPS patients in particular benefit from a clinical setting that takes monitoring seriously, because the comorbidity profile is often more complex than for purely psychiatric indications.

What protocols look like in a Nashville outpatient setting

Most CRPS patients we see are not candidates for the multi-day continuous infusion model used by Sigtermans, both because of the inpatient logistics and because outpatient evidence has matured since 2009. The starting framework we discuss draws from the Schwartzman-style outpatient series: a sequence of infusions delivered over a defined window, with doses calibrated to the individual’s tolerance and clinical response.

A typical consultation covers your CRPS history (Type 1 vs Type 2, duration, prior treatments), current medication list, functional goals, and what realistic response would look like for you. We are direct about uncertainty: we cannot predict who will respond, and we will not pretend otherwise. Roughly a third of CRPS patients in the published literature are non-responders, and we tell patients this before they start, not after.

Sessions take place in private rooms at our Franklin clinic. Walter White and Wilma, our therapy dogs, are around for patients who want their company. Marla Peterson, CRNA, is in the room and oversees the session with anesthesia-level monitoring. You will need a driver. Most patients return to normal activities the following day, though CRPS patients with significant baseline limb dysfunction may need longer to assess functional changes.

CRPS is one of the few off-label ketamine indications with multiple randomized controlled trials behind it. The data is not perfect, the durability is variable, and roughly a third of patients are non-responders — but for refractory cases, evidence supports ketamine as a serious option rather than a hopeful one. — Synthesizing Sigtermans 2009, Schwartzman 2009, and the RSDSA clinical position

Honest expectations and what comes next

We want to be straightforward about what ketamine can and cannot do for CRPS at this stage of the evidence.

If you have been working with a pain physician, a neurologist, or a CRPS specialist, we coordinate. We are an outpatient ketamine clinic, not a comprehensive pain practice, and we work better as one tool inside a broader treatment structure than as a stand-alone solution. To get a sense of how we structure care, our overview of how ketamine therapy works at our clinic walks through the consultation, the session itself, and what happens between visits.