Low Dose Naltrexone Therapy for Complex Regional Pain Syndrome

Naltrexone, an FDA-approved medication since 1984, is classically prescribed in daily doses of at least 50 mg to mediate opiate and alcohol abuse as part of a comprehensive treatment program. By acting as an antagonist in the body, full-strength naltrexone competitively binds to opioid receptors and blocks the effects of opioid-classified drugs, thereby helping to reduce reliance and addiction. In much lower doses (1.5 - 4.5mg per day), naltrexone has been seen to reduce inflammation and nerve pain by instead blocking a different set of receptors involved in cytokine release and uptake. The exact mechanism of naltrexone's ability to decrease inflammation, swelling, and chronic nerve pain is unknown; however further research is being done to discover more. When healthcare providers prescribe naltrexone in these low doses, the medication is referred to as low-dose naltrexone-or LDN.

As of recently, healthcare providers have begun looking at the efficacy of low-dose naltrexone when treating pain caused primarily by the nervous system, referred to as neuropathic pain. Complex Regional Pain Syndrome (CRPS) is a debilitating chronic pain condition caused by dysfunction of or damage to the nervous system. CRPS can be caused by an injury, surgery, or have no obvious cause at all. CRPS typically affects a specific area of the body, such as the hands or feet, and symptoms may include extreme sensitivity, pins-and-needles sensation, color and/or temperature changes, swelling, and stinging. One treatment route commonly prescribed for CRPS is an anti-neuropathic medication regime of Gabapentin or Pregabalin-medications prescribed to specifically ease nerve-related pain. Targeted nerve blocks and epidural injections are other common treatments physiatrists and pain providers will perform for CRPS patients, often in conjunction with medication and physical therapy for a comprehensive pain management plan. However, for those who cannot take anti-neuropathic medications and are hesitant to pursue more invasive routes like nerve blocks or spinal cord stimulations, there is a lack of available treatment options which makes pain management uncertain and inconsistent. In an effort to diversify available treatments, there is a budding interest in the role that low-dose naltrexone may play in reducing chronic pain associated with CRPS.

There is currently only one other low-dose naltrexone study being conducted with Complex Regional Pain Syndrome patients as the primary study population. Dr. Sean Mackey is leading this study through the Stanford Division of Pain Medicine, and the study is still in the process of enrolling eligible patients. Published case studies demonstrate the promising nature of the drug in a multi-modal treatment course and suggest that more extensive research on the effectiveness of low-dose naltrexone would be beneficial. When physicians wish to incorporate LDN into the treatment course for a CRPS patient, they have additional barriers to cross because naltrexone is FDA-approved only for alcohol and opioid-use disorders. The lack of FDA-approval for naltrexone in CRPS treatment creates limited accessibility to the drug, the need for compounding pharmacy involvement, and a lack of education surrounding low-dose naltrexone in the CRPS and chronic pain community. Conducting controlled clinical trials and thereby learning more about the efficacy of low-dose naltrexone and possible side effects or adverse reactions would help establish LDN as another treatment possibility for frustrated patients dealing with this chronic pain syndrome.

Our feasibility study has two purposes: to evaluate the potential of LDN as CRPS pain management, and to evaluate whether such a long-term interventional drug study can be conducted at the Hospital for Special Surgery (HSS). Not only will the investigators be collecting pain scores over time to better understand whether LDN may help improve pain and symptom severity, but the investigators will also be collecting information regarding how many patients enroll, how many patients remain enrolled during the duration of the study, why patients may un-enroll, and how compliant patients are with taking the daily study medication. This study will be requesting that each enrolled patient take a medication every day for 6 months, consistently attend office visits when requested, and take record of how often they miss a dose. To date and to our knowledge, no similar study requiring such extensive participation and long-term medication consumption has been conducted at HSS-whether in the main hospital or through an outpatient clinic. In order to expand on the knowledge base HSS has developed regarding its chronic pain patient population, long-term research utilizing placebo and study medication is essential. Prior to conducting larger-scale interventional drug studies, it is imperative that the workflow is streamlined and established protocols are in place. Aside from looking into the LDN-CRPS relationship, the main purpose of this feasibility study is to develop an infrastructure to demonstrate that interventional drug studies of this magnitude are possible at HSS, establish novel protocols and standard operating procedures, and gauge the receptiveness of chronic pain patients to studies of this kind at HSS.

Over the course of two years, a total of 40 patients recently diagnosed with CRPS at the 75th St HSS outpatient location will be enrolled and randomized to receive either capsules with the active low-dose naltrexone medication, or placebo capsules which do not contain any active ingredient. The study medication will be supplied to study patients in addition to any standard CRPS therapies, including physical therapy, medication management, and interventional therapies. Enrolled patients will take the medication every day for a total of 6 months and will attend standard of care office visits after 1 month, after 3 months, and after 6 months. Before each visit, patients will be asked to record their daily average pain for one week leading up to the visit. In between office visits, a study team member will be calling the patients to record medication consumption compliance, pain scores, questionnaire responses, adverse reactions, and any side effects. Questionnaires will include PROMIS-10, S-LANSS, and an NRS screening. A study team member will also be calling patients as a reminder to record in their 7-day pain diary when necessary. A major component of the study protocol is the titration schedule-a schedule that defines how the drug dosage will increase over time-which Dr. Semih Gungor, the principal physician investigator, has already established at his clinic. While it is subject to change depending on the patient's CRPS symptom progression and medication-related side effects, the titration schedule built into the study protocol will be starting at 1.5mg during the 1st month, increasing to 3mg the 2nd month, and finally up to 4.5mg the 3rd month and beyond. The purpose of this titration schedule is to limit the side effects a patient may feel when starting on naltrexone and to gradually introduce them to the drug to facilitate a long-term treatment.

Through the enrollment of study patients and successful dispensation of daily medication over a 6-month time period, our study aims to collect preliminary data on pain scores, symptom severity, and side-effects in patients randomized to LDN vs. placebo, as well as determine the feasibility of conducting a long-term interventional drug study-with the goal of expanding future research opportunities at HSS and supplementing treatment courses for those struggling with this often debilitating chronic pain syndrome.