Clinical Focus

  • Pain Management
  • Neuropathic Pain
  • Anesthesia

Academic Appointments

Professional Education

  • Medical Education:Columbia University (1998) NY
  • Fellowship:Stanford University School of Medicine (2003) CA
  • Residency:Stanford University School of Medicine (2002) CA
  • Board Certification: Pain Medicine, American Board of Anesthesiology (2004)
  • Internship:Stanford University School of Medicine (1999) CA
  • Board Certification: Anesthesia, American Board of Anesthesiology (2003)
  • M.S., Stanford University, Clinical Epidemiology (2006)
  • M.D., Columbia University (1998)

Research & Scholarship

Current Research and Scholarly Interests

Factors causing prolonged post-surgical pain and prolonged opioid use.

Some patients following routine surgery will experience chronic pain, and/or prolonged opioid use. This research done at Stanford Hospital and the Palo Alto VA Hospital will identify factors that delay pain resolution and opioid cessation in patients following surgery. Data collection is currently ongoing in the pilot stage, without funding. This clinical study offers abundant opportunities for undergraduate students, medical students, or residents to contribute meaningfully in collecting data from patients, and analyzing results. Local collaborators include:

Sean Mackey Pain Medicine
John PollardAnesthesia
Keith HumphreysAddiction
Jodie TraftonAddiction/Pain Research
Peter BarelkaPain Medicine/ anesthesia
Stuart GoodmanOrthopedic surgery
George YangGeneral Surgery
Fred DirbasBreast Surgery

Dates: January 2007- Present

Brainstem Mechanisms of Analgesia in Patients with Post-Surgical Nerve Pain: an fMRI study.

Only a proportion of patients with neuropathic pain respond to conventional anti-neuropathic pain medications--most of which are sodium channel blockers. The mechanisms responsible for analgesia in response to a sodium channel blocker remain unknown. In this translational research at Stanford Hospital we are using functional MRI to define supraspinal changes in neuropathic pain patients specifically associated with analgesic responses to systemic lidocaine--a prototypical sodium channel blocker. Local Collaborators include:

Sean MackeyPain Medicine

Funding: Foundation for Anesthesia Education and Research Mentored Research Training Grant.

Dates: January 2007-Present

Botulinum Toxin Sympathectomy for Chronic Sympathetically Maintained Pain. This is a prospective, double blind crossover trial of whether Botox improves duration of analgesia following lumbar sympathetic block. The study is centered at Stanford Hospital. Trial enrollment is nearing completion. Opportunities exist for students and residents to assist in data analysis. Collaborators include:

Sean MackeyPain Medicine
David ClarkPain Medicine

Dates: January 2005-Present

Clinical Trials

  • Study of T3 for the Treatment of Fibromyalgia Not Recruiting

    Determine if T3 - the active form of thyroid hormone - is beneficial in fibromyalgia. Determine the feasibility and promise of an appropriately powered future prospective randomized controlled study of using T3 (the active form of thyroid hormone) for the treatment of fibromyalgia. We specifically aim to assess the feasibility, cost, obstacles and promise of conducting a prospective controlled study in the future.

    Stanford is currently not accepting patients for this trial. For more information, please contact Rebecca McCue, (650) 724 - 0522.

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  • Subcutaneous Botulinum Toxin for Cutaneous Allodynia - Enriched Responder Trial Not Recruiting

    Superficial injection of Botulinum toxin has been advocated for cosmetic purposes but has also been reported to be helpful for some pain conditions. The investigators have observed prolonged profound analgesia following subcutaneous superficial injection of Botulinum Toxin Type A (BTA) in patients with certain types of neuropathic pain. the investigators propose to study if addition of BTA extends pain relief compared to placebo when injected subcutaneously into areas of cutaneous allodynia (the property that a normally non-noxious stimulus is perceived as painful).

    Stanford is currently not accepting patients for this trial. For more information, please contact Charlie Wang, (650) 723 - 8250.

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  • Stanford Accelerated Recovery Trial (START) Recruiting

    The goal of this study is to determine whether administering Gabapentin prior to surgery affects duration of pain and opioid use post-surgery. The investigators aim to compare gabapentin to placebo in a prospective, randomized clinical trial in which patients will be followed post-surgery until pain resolves and opioid use ceases.

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  • Effect of IV Lidocaine Infusions on Pain Not Recruiting

    Our goals for this study involve using intravenous lidocaine as it is normally used in the Stanford Pain Management Center to assess the effect of intravenous lidocaine on chronic pain. Studies have been done determining the efficacy of intravenous lidocaine for treating pain but little research has been done to determine the effects of an intravenous lidocaine infusion on the different components of the pain experience. Our study will incorporate psychophysical and behavioral testing both before and during the infusions of lidocaine to determine changes in mood. In addition, we will use functional magnetic resonance imaging to observe what changes occur in the brain during a lidocaine infusion.

    Stanford is currently not accepting patients for this trial.

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  • A Pilot Clinical Trial of Sympathetic Blockade With Botulinum Toxin Type A to Treat Complex Regional Pain Syndrome (CRPS): a Randomized, Double-Blind, Controlled, Crossover Trial. Not Recruiting

    Lumbar sympathetic blocks are part of the standard of care for treating patients with sympathetically-maintained pain (e.g. in complex regional pain syndrome or reflex sympathetic dystrophy- RSD). In these patients lower extremity pain can be reduced or abolished temporarily by blocking sympathetic nerves by doing a lumbar sympathetic block. Patients who respond only transiently to sympathetic blocks often choose between potentially dangerous lumbar sympathetic block with neurolytic agents, surgical sympathectomy, continued severe refractory debilitating pain or other risky invasive surgical procedures such as spinal cord electrical stimulation.. It is hypothesized that Botulinum Toxin Type A (BTA) injected in a lumbar sympathetic block can provide extended sympathetic blockade and thus pain relief. This pilot study aims to see if BTA can be used safely in lower extremity sympathetic blocks, and might be useful in providing prolonged pain relief.

    Stanford is currently not accepting patients for this trial. For more information, please contact Ian Carroll, (650) 498 - 6885.

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  • Subcutaneous Botulinum Toxin for Cutaneous Allodynia Not Recruiting

    Superficial injection of Botulinum toxin has been advocated for cosmetic purposes but has also been reported to be helpful for some pain conditions. The investigators have observed prolonged profound analgesia following subcutaneous superficial injection of Botulinum Toxin Type A (BTA) in patients with certain types of neuropathic pain. The investigators propose to study if addition of BTA extends pain relief compared to placebo when injected subcutaneously into areas of cutaneous allodynia (the property that a normally non-noxious stimulus is perceived as painful).

    Stanford is currently not accepting patients for this trial. For more information, please contact Rachel Moericke, (650) 724 - 0522.

    View full details


2014-15 Courses


Journal Articles

  • Pain Quality Predicts Lidocaine Analgesia among Patients with Suspected Neuropathic Pain PAIN MEDICINE Carroll, I. R., Younger, J. W., Mackey, S. C. 2010; 11 (4): 617-621


    Oral sodium channel blockers have shown mixed results in randomized controlled trials despite the known importance of sodium channels in generating pain. We hypothesized that differing baseline pain qualities (e.g. "stabbing" vs "dull") might define specific subgroups responsive to intravenous (IV) lidocaine-a potent sodium channel blocker.A prospective cohort study of 71 patient with chronic pain suspected of being neuropathic were recruited between January 2003 and July 2007 and underwent lidocaine infusions at Stanford University Hospital in a single-blind nonrandomized fashion. Baseline sensory pain qualities were measured with the Short-Form McGill Pain Questionnaire (SF-MPQ). Pain intensity was measured with a visual analog scale (VAS).Factor analysis demonstrated two underlying pain quality factors among SF-MPQ sensory items: a heavy pain and a stabbing pain. Baseline heavy pain quality, but not stabbing quality predicted subsequent relief of pain intensity in response to lidocaine. In contrast, these factors did not predict divergent analgesic responses to placebo infusions. In response to each 1 mcg/mL increase in lidocaine plasma level, patients with high heavy pain quality drop their VAS 0.24 (95% CI 0.05-0.43) more points than those with low heavy pain quality (P < 0.013)."Heavy" pain quality may indentify patients with enhanced lidocaine responsiveness. Pain quality may identify subgroups among patients with suspected neuropathic pain responsive to IV lidocaine. Further investigation is warranted to validate and extend these findings.

    View details for Web of Science ID 000276223500020

    View details for PubMedID 20210867

  • Serratus muscle stimulation effectively treats notalgia paresthetica caused by long thoracic nerve dysfunction: a case series. Journal of brachial plexus and peripheral nerve injury Wang, C. K., Gowda, A., Barad, M., Mackey, S. C., Carroll, I. R. 2009; 4: 17-?


    Currently, notalgia paresthetica (NP) is a poorly-understood condition diagnosed on the basis of pruritus, pain, or both, in the area medial to the scapula and lateral to the thoracic spine. It has been proposed that NP is caused by degenerative changes to the T2-T6 vertebrae, genetic disposition, or nerve entrapment of the posterior rami of spinal nerves arising at T2-T6. Despite considerable research, the etiology of NP remains unclear, and a multitude of different treatment modalities have correspondingly met with varying degrees of success. Here we demonstrate that NP can be caused by long thoracic nerve injury leading to serratus anterior dysfunction, and that electrical muscle stimulation (EMS) of the serratus anterior can successfully and conservatively treat NP. In four cases of NP with known injury to the long thoracic nerve we performed transcutaneous EMS to the serratus anterior in an area far lateral to the site of pain and pruritus, resulting in significant and rapid pain relief. These findings are the first to identify long thoracic nerve injury as a cause for notalgia paresthetica and electrical muscle stimulation of the serratus anterior as a possible treatment, and we discuss the implications of these findings on better diagnosing and treating notalgia paresthetica.

    View details for DOI 10.1186/1749-7221-4-17

    View details for PubMedID 19772656

  • Postoperative Pain Following Foot and Ankle Surgery: A Prospective Study FOOT & ANKLE INTERNATIONAL Chou, L. B., Wagner, D., Witten, D. M., Martinez-Diaz, G. J., Brook, N. S., Toussaint, M., Carroll, I. R. 2008; 29 (11): 1063-1068


    Orthopaedic procedures have been reported to have the highest incidence of pain compared to other types of operations. There are limited studies in the literature that investigate postoperative pain.A prospective study of 98 patients undergoing orthopedic foot and ankle operations was undertaken to evaluate their pain experience. A Short-Form McGill Pain Questionnaire (SF-MPQ) was administered preoperatively and postoperatively.The results showed that patients who experienced pain before the operation anticipated feeling higher pain intensity immediately postoperatively. Patients, on average, experienced higher pain intensity 3 days after the operation than anticipated. The postoperative pain intensity at 3 days was the most severe, while postoperative pain intensity at 6 weeks was the least severe. Age, gender and preoperative diagnosis (acute versus chronic) did not have a significant effect on the severity of pain that patients experienced. Six weeks following the operation, the majority of patients felt no pain. In addition, the severity of preoperative pain was highly predictive of their anticipated postoperative pain and 6-week postoperative pain, and both preoperative pain and anticipated pain predict higher immediate postoperative pain.The intensity of patients' preoperative pain was predictive of the anticipated postoperative pain. Patients' preoperative pain and anticipated postoperative pain were independently predictive of the 3-day postoperative pain. The higher pain intensity a patient experienced preoperatively suggested that their postoperative pain severity would be greater. Therefore, surgeons should be aware of these findings when treating postoperative pain after orthopaedic foot and ankle operations.

    View details for DOI 10.3113/FAI.2008.1063

    View details for Web of Science ID 000260714000002

    View details for PubMedID 19026197

  • Urinalysis vs urine protein-creatinine ratio to predict significant proteinuria in pregnancy JOURNAL OF PERINATOLOGY Dwyer, B. K., Gorman, M., Carroll, I. R., Druzin, M. 2008; 28 (7): 461-467


    To compare the urine protein-creatinine ratio with urinalysis to predict significant proteinuria (>or=300 mg per day).A total of 116 paired spot urine samples and 24-h urine collections were obtained prospectively from women at risk for preeclampsia. Urine protein-creatinine ratio and urinalysis were compared to the 24-h urine collection.The urine protein-creatinine ratio had better discriminatory power than urinalysis: the receiver operating characteristic curve had a greater area under the curve, 0.89 (95% confidence interval (CI) 0.83 to 0.95) vs 0.71 (95% CI 0.64 to 0.77, P<0.001). When matched for clinically relevant specificity, urine protein-creatinine ratio (cutoff >or=0.28) is more sensitive than urinalysis (cutoff >or=1+): 66 vs 41%, P=0.001 (with 95 and 100% specificity, respectively). Furthermore, the urine protein-creatinine ratio predicted the absence or presence of proteinuria in 64% of patients; urinalysis predicted this in only 19%.The urine protein-creatinine ratio is a better screening test. It provides early information for more patients.

    View details for DOI 10.1038/jp.2008.4

    View details for Web of Science ID 000257271500003

    View details for PubMedID 18288120

  • Mexiletine therapy for chronic pain: Survival analysis identifies factors predicting clinical success JOURNAL OF PAIN AND SYMPTOM MANAGEMENT Carroll, I. R., Kaplan, K. M., Mackey, S. C. 2008; 35 (3): 321-326


    Mexiletine, a sodium channel blocker, treats neuropathic pain but its clinical value has been questioned due to its significant side effects and limited efficacy. We hypothesized that ongoing therapy with mexiletine would have limited patient acceptance, but that an analgesic response to intravenous (IV) lidocaine (a pharmacologically similar drug) would identify patients most likely to choose ongoing therapy with mexiletine. We identified a cohort of 37 patients with neuropathic pain who underwent IV lidocaine infusions at our institution and were subsequently prescribed mexiletine. Time until discontinuation of mexiletine was used as the primary endpoint. Time until discontinuation is a clinically relevant, discrete, objective endpoint gaining acceptance as a metric for assessing clinical performance of drugs with significant side effects and limited efficacy. We used the techniques of survival analysis to determine factors that predicted continued therapy with mexiletine. Median time to discontinuation of mexiletine was only 43 days. A stronger analgesic response to IV lidocaine significantly predicted continued acceptance of mexiletine therapy. Decreasing age and male gender also predicted continued acceptance of mexiletine therapy. Analyzing time to mexiletine discontinuation uncovers important limitations in mexiletine's clinical performance missed by studies with conventional endpoints, such as change in pain score. Despite claims of efficacy, acceptance of mexiletine therapy is poor overall. Test infusions with lidocaine identify patients most likely to continue mexiletine therapy. Further work is needed to confirm these results and evaluate the relative acceptance of mexiletine vs. other treatments of neuropathic pain.

    View details for DOI 10.1016/j.jpainsymman.2007.04.022

    View details for Web of Science ID 000253919000016

    View details for PubMedID 18222627

  • Multivariate analysis of chronic pain patients undergoing lidocaine infusions: Increasing pain severity and advancing age predict likelihood of clinically meaningful analgesia CLINICAL JOURNAL OF PAIN Carroll, I., Gaeta, R., Mackey, S. 2007; 23 (8): 702-706


    The proportion of chronic pain patients with suspected neuropathic pain who will have clinically meaningful pain relief with intravenous (IV) lidocaine and the clinical characteristics that identify these patients have not been described previously.We conducted a cohort study of 99 patients who underwent IV lidocaine infusions for suspected neuropathic pain. An 11-point Numerical Rating Score (NRS) of pain intensity was recorded at the beginning and end of each infusion. A predefined literature-based criteria for "clinically meaningful" reductions in pain score was used to classify patients as responders or nonresponders. Multivariate logistic regression was used to determine clinical variables that predicted an increased likelihood of being a lidocaine responder.The mean reduction in NRS during lidocaine infusions was 2.34 (95% confidence interval 2.83-1.85, P<0.001). Forty-two percent of patients (95% confidence interval 32.5%-52.8%) had NRS reductions of 30% or greater and met the predefined criteria as lidocaine responders. Univariate and multivariate analyses indicated that advancing age and pain severity significantly increased the odds of being a lidocaine responder. Controlled for all other factors, each decade of advancing age increased the odds of being a lidocaine responder by 36%. Each 1-point increase, on an 11-point scale of baseline pain severity, increased the odds of being a lidocaine responder by 29%.IV lidocaine effectively reduces pain in a minority of patients suspected of having neuropathic pain. Pain severity and patient age can be used to target therapy to those most likely to respond.

    View details for Web of Science ID 000249743000009

    View details for PubMedID 17885349

  • Intravenous lidocaine for neuropathic pain: diagnostic utility and therapeutic efficacy. Current pain and headache reports Carroll, I. 2007; 11 (1): 20-24


    Lidocaine is a use-dependent sodium channel blocker that produces analgesia when administered intravenously to patients with neuropathic pain. This article reviews the role and limitations of intravenous lidocaine infusions for neuropathic pain. Lidocaine infusions rarely provide relief that persists significantly beyond the duration of the infusion. Diagnostically, systemic lidocaine may help establish the presence of neuropathic pain and the responsivity to oral sodium channel blockade. However, the data supporting diagnostic infusions remain sparse. Therapeutically, infusions should generally be restricted to patients with neuropathic pain who are unable to take oral medication.

    View details for PubMedID 17214917

  • Celiac plexus block for visceral pain. Current pain and headache reports Carroll, I. 2006; 10 (1): 20-25


    Celiac plexus block has long been used to provide analgesia for upper abdominal pain. In particular, neurolytic celiac plexus block has been advocated for pancreatic cancer pain. In this article, recent advances clarifying the role and limitations of neurolytic celiac plexus block are reviewed. Neurolytic celiac plexus block provides persistent augmented analgesia when used as an adjunct to systemic opiates, but does not reliably decrease opiate requirements. In addition, neurolytic celiac plexus block may prolong survival, but the data supporting this remain controversial. The optimal technique for accomplishing neurolytic celiac plexus block remains undetermined.

    View details for PubMedID 16499826

  • A vaccine to prevent herpes zoster NEW ENGLAND JOURNAL OF MEDICINE Carroll, I., Gaeta, R., Mackey, S. 2005; 353 (13): 1414-1415

    View details for Web of Science ID 000232146200022

    View details for PubMedID 16196123

  • Management of perioperative pain in patients chronically consuming opioids REGIONAL ANESTHESIA AND PAIN MEDICINE Carroll, I. R., Angst, M. S., Clark, J. D. 2004; 29 (6): 576-591


    The prevalence of licit and illicit opioid use is growing, and a greater percentage of chronically opioid-consuming patients are presenting for surgery. These patients can be expected to experience increased postoperative pain, greater postoperative opioid consumption, and prolonged use of healthcare resources for managing their pain.Achieving adequate pain control in these patients can be challenging because commonly used strategies for alleviating postoperative pain may have diminished effectiveness. We explore the prevalence and characteristics of opioid use in the United States and discuss its impact on the perioperative management of pain. We examine mechanistically why adequate perioperative pain control in chronically opioid-consuming patients may be difficult.We present strategies for providing adequate analgesia to these patients that include the optimal use of opioids, adjuvant medications, and regional anesthetic techniques.

    View details for DOI 10.1016/j.rapm.2004.06.009

    View details for Web of Science ID 000226144300011

    View details for PubMedID 15635517

  • HIV Tat represses transcription of the beta(2)-microglobulin promoter MOLECULAR IMMUNOLOGY Carroll, I. R., Wang, J., Howcroft, T. K., Singer, D. S. 1998; 35 (18): 1171-1178


    The MHC class I complex, which binds and presents peptide antigen, is composed of a class I heavy chain and the beta2-microglobulin light chain. HIV-1, which induces a profound immunodeficiency in infected individuals, encodes proteins that cause decreased expression of class I heavy chain. We now report that the HIV Tat protein, which is a potent transactivator of viral transcription, is also a potent repressor of the beta2-microglobulin gene. Repression is mediated through the basal promoter of the beta2-microglobulin gene, which is shown to be predominantly regulated by an initiator element. Tat repression is further augmented by the short viral transcript, TAR, which interacts with Tat. Tat-mediated repression of beta2-microglobulin expression, together with its known repression of class I gene transcription, provides an effective mechanism by which HIV could prevent cell surface expression of the MHC class I complex and avoid immune surveillance.

    View details for Web of Science ID 000079458800003

    View details for PubMedID 10199391

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