One of the most frustrating aspects of treating complex regional pain syndrome (CRPS) is its variable nature, challenging practitioners to find a regimen that will provide enough analgesia to allow patients to resume normal activities. A case report presented here described the first-ever reported placement of an ultrasound-guided continuous superficial radial nerve block for the treatment of CRPS. A group of practitioners seems to have added another possible approach to the anesthesiologist’s armamentarium.
“We don’t know why some people develop CRPS from certain injuries and others don’t,” said Daryl S. Henshaw, MD, assistant professor of anesthesia at Wake Forest School of Medicine, in Winston-Salem, N.C. “CRPS is a multifaceted connection between various systems. The emotional system, the pain system and the sympathetic system all get out of balance, and the patient spirals down[ward]. And it’s very difficult to treat because it’s so multifactorial.”
CRPS Still a Mystery
As Dr. Henshaw related, CRPS is more common after major traumatic injuries but also can occur after normally innocuous procedures. And while most patients will see their symptoms abate within the first year, a subset of patients will suffer the effects of CRPS longer, leading to recalcitrant pain and loss of function. These patients often exhaust both medical and surgical treatment options in hopes of finding relief, leaving clinicians scratching their heads to find alternate analgesic routes.
“One of our orthopedic surgeons was caring for a patient who had a very clearly defined injury,” Dr. Henshaw said. The 46-year-old woman had a history of CRPS type II (causalgia; known neural insult) of the right arm and hand after an injury to her superficial radial nerve during a previous venous cannulation. She had experienced intermittent swelling and functional loss of the hand and forearm.
The woman was on an analgesic regimen that included gabapentin, tramadol and duloxetine, although she occasionally needed oral hydromorphone, which she used consistently for several weeks before her admission to the institution. Her baseline numeric rating scale pain scores were 7 of 10 at rest and 10 of 10 with movement. Her pain was primarily experienced as a burning sensation in the dorsum of the hand and in the forearm, with occasional radiation to the upper arm along the track of the radial nerve.
“Historically what we’ve done is a block near the brachial plexus,” Dr. Henshaw told Anesthesiology News. “But that puts the entire arm to sleep, and then the patient doesn’t have a lot of function.”
Given the woman’s injury to the superficial radial nerve, the clinicians used ultrasound to identify the nerve at the junction of the middle and proximal thirds of the forearm, and confirmed by tracing the nerve proximally to the radial nerve and distally to the wrist. A 9-cm, 17-gauge Tuohy needle was inserted from the lateral side of the arm and advanced until it abutted the superficial radial nerve. Then a 19-gauge, nonstimulating peripheral nerve catheter was threaded into close proximity to the nerve.
Initial injection of local anesthetic included 10 mL of 1.5% mepivacaine with 1:200,000 epinephrine, followed by a continuous infusion of 0.4% ropivacaine with 0.5 mcg/mL of clonidine (6 mL/h). Adjuvant medications included a continuous infusion of intravenous ketamine (15 mg/h), 5 mg oral diazepam every six hours, 100 mg oral acetaminophen every six hours, 50 mg oral tramadol every six hours, 75 mg pregabalin (Lyrica, Pfizer) twice daily and 200 mg celecoxib twice daily. The woman was hospitalized for three days, and then discharged home for another three days of treatment with ambulatory infusion of local anesthetic.
Dramatic Early Improvement
As reported at the 2016 annual meeting of the American Society of Regional Anesthesia and Pain Medicine (abstract 1567), the patient was able to tolerate passive movement of her right hand and forearm by 30 minutes after the block, and her pain scores dropped to 0 with rest and movement. One day after the block, her pain scores were recorded as 0 of 10 with rest and 2 of 10 with movement. Her pain was localized to the anatomic “snuff box”; a 10-mL bolus was administered from the pump, and the basal rate was increased to 8 mL per hour.
“So once we made her superficial radial nerve insensate, her pain went down considerably,” Dr. Henshaw said. “But it also allowed her to be functional. So she was not only able to participate in therapy and do passive range-of-motion exercises, but she could also do active range-of-motion [exercises] and use her hand, almost for the first time in years. Her husband actually said three days later that it was the first time he’d held her hand in years.”
Three days after block placement, the superficial radial nerve catheter was connected to an elastomeric pump with 0.4% ropivacaine and 0.5 mcg/mL of clonidine at 8 mL per hour. The patient was then discharged home, where analgesia continued to be of good quality (pain scale scores, 1-3 of 10).
“The patient followed up with her orthopedic surgeon at about 15 days after we placed the block,” Dr. Henshaw added. “Although her pain score had gone up to around a 5, it was still lower than her baseline pain scores, which were in the 7-to-8 range. My guess is that her pain has likely returned to where it started. But the procedure gave us a good indication of how she responded while the catheter was in place.”
And while it remains to be seen whether the superficial radial nerve block proves useful in similar CRPS patients, the case helps illustrate the potential of ultrasound guidance in these situations. “The ultrasound has allowed us to find nerves that we otherwise couldn’t put catheters on, and that’s the interesting thing about the superficial radial nerve,” he added. “There’s no other way to put a catheter on that nerve other than to view it with ultrasound or some other imaging modality.
“But the best part about this approach is that it’s given the patient an avenue through which she can approach her next line of therapy. And that means we’ve accomplished what we hoped to do; we didn’t permanently fix her, but we did give her some insight into her injury and how her body will respond.”
Eric Schwenk, MD, assistant professor of anesthesiology and director of orthopedic anesthesia at the Sidney Kimmel Medical College at Thomas Jefferson University in Philadelphia, was impressed that Dr. Henshaw and his colleagues were able to accomplish relief via this technique. “This would have been impossible pre-ultrasound guidance,” Dr. Schwenk said. “I commend them for being innovative and minimizing this patient’s dysfunction while providing excellent analgesia.
“Of course, the biggest and most important questions will be what her pain scores and functional limitations are a month or several months after the procedure,” he said. “Is there some role for a series of radial nerve blocks performed months apart, similar to what is already done at some centers using ketamine infusions for CRPS patients? Nevertheless, the authors may be onto something here.”
The full case report is now available online in the Journal of Pain & Palliative Care Pharmacotherapy (www.tandfonline.com/?doi/?abs/?10.3109/?15360288.2016.1173755).