R W McCallum

Texas Tech University Health Sciences Center, El Paso, Texas, United States

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Publications (436)2765.05 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: Background There is increasing evidence for specific cellular changes in the stomach of patients with diabetic (DG) and idiopathic (IG) gastroparesis. The most significant findings are loss of interstitial cells of Cajal (ICC), neuronal abnormalities, and an immune cellular infiltrate. Studies done in diabetic mice have shown a cytoprotective effect of CD206+ M2 macrophages. To quantify overall immune cellular infiltrate, identify macrophage populations, and quantify CD206+ and iNOS+ cells. To investigate associations between cellular phenotypes and ICC.Methods Full thickness gastric body biopsies were obtained from non-diabetic controls (C), diabetic controls (DC), DG, and IG patients. Sections were labeled for CD45, CD206, Kit, iNOS, and putative human macrophage markers (HAM56, CD68, and EMR1). Immunoreactive cells were quantified from the circular muscle layer.Key ResultsSignificantly fewer ICC were detected in DG and IG tissues, but there were no differences in the numbers of cells immunoreactive for other markers between patient groups. There was a significant correlation between the number of CD206+ cells and ICC in DG and DC patients, but not in C and IG and a significant correlation between iNOS+ cells and ICC in the DC group, but not the other groups. CD68 and HAM56 reliably labeled the same cell populations, but EMR1 labeled other cell types.Conclusions & InferencesDepletion of ICC and correlation with changes in CD206+ cell numbers in DC and DG patients suggests that in humans, like mice, CD206+ macrophages may play a cytoprotective role in diabetes. These findings may lead to novel therapeutic options, targeting alternatively activated macrophages.
    Neurogastroenterology and Motility 07/2014; · 2.94 Impact Factor
  • Yan Sun, Gengqing Song, Richard W McCallum
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    ABSTRACT: Introduction: The treatment for functional dyspepsia (FD) (indigestion) remains unsatisfactory. Acotiamide is a new prokinetic that has been recently approved and used in Japan for the treatment of FD. Areas covered: This review introduces the pharmacodynamics, pharmacokinetics and efficacy data from current clinical trials from literature sourced using the PubMed search tools. Future principles for developing drugs and designing clinical trials to test them for treating FD are also discussed. Expert opinion: Acotiamide can contribute to the treatment of the specific subset of symptoms defined as postprandial FD by reducing the impaired fundic relaxation and accommodation after eating. The agent has the added benefit of a very good safety profile.
    Expert Opinion on Drug Metabolism &amp Toxicology 05/2014; · 2.93 Impact Factor
  • Reza A Hejazi, Richard W McCallum
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    ABSTRACT: Cyclic vomiting syndrome is a disorder characterized by recurrent episodes of severe nausea and vomiting separated by symptom-free periods. Our aims were to review treatments of adult cyclic vomiting syndrome as well as to identify areas for further clinical research and the unanswered questions in this field. We conducted a PubMed search using such keywords as "cyclic vomiting syndrome," "nausea," "vomiting," "treatment," "trigger factors" and "tricyclic antidepressants" and combined this information with the knowledge and clinical research from the authors. Available data show that in adult cyclic vomiting syndrome, there is an impressive and sustained response to high-dose tricyclic antidepressants. In up to 13 % who are regarded as poor responders to tricyclic antidepressants, a predictable profile can be identified related to coexisting psychological disorders, marijuana use, poorly controlled migraine headache or chronic narcotic use. Cyclic vomiting syndrome in adults is being an increasingly recognized entity. Tricyclic antidepressants are the main treatment for controlling symptoms. Eliminating and addressing trigger factors are an essential part of management.
    Experimental Brain Research 05/2014; · 2.17 Impact Factor
  • Joseph Sunny, Cesar J. Garcia, Richard W. McCallum
    Gastroenterology 05/2014; 146(5):S-466. · 13.93 Impact Factor
  • Gastroenterology 05/2014; 146(5):S-610. · 13.93 Impact Factor
  • Gastroenterology 05/2014; 146(5):S-614. · 13.93 Impact Factor
  • Reza A Hejazi, Richard W McCallum
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    ABSTRACT: : Rumination is a normal and common phenomenon among ruminant animals; but in humans, it is always regarded as symptom indicative of abnormal function of the upper gastrointestinal tract, and understanding of the mechanisms explaining this event are still evolving. Learning-based theories, organic factors such as gastroesophageal reflux disease and psychological disturbances (eg, depression, anxiety) and the role of life stresses have been postulated as potential mechanisms of rumination. In this review, we take the approach that rumination syndrome is a distinct and discrete functional gastroduodenal disorder. We review current concepts of the pathophysiology of this entity and diagnostic approaches, then detail the treatment paradigms that have been pursued in rumination syndrome in adults. Patients with rumination syndrome have a very distinct set of symptoms. It was focused on the immediate postprandial period, but recently, there is an awareness of an expanding spectrum of the clinical presentation. This includes the concept of "conditioned vomiting" occurring in the setting of delayed gastric emptying (gastroparesis). Physicians' awareness of rumination syndrome is essential in the diagnosis and management of this disorder. Stress and psychological aspects in rumination syndrome are invariably in the background and have to be addressed. The crucial steps in the treatment strategy for rumination syndrome rely on reassurance, education and a physiologic explanation to the patient and family that this is not a "disease," followed by behavioral and relaxation programs and addressing stress factors.
    The American Journal of the Medical Sciences 03/2014; · 1.52 Impact Factor
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    ABSTRACT: Background Cyclic vomiting syndrome (CVS) in adults is a disorder characterized by recurrent and stereotypic episodes of severe nausea, vomiting and abdominal pain separated by symptom-free intervals. Our goal was to investigate gastric emptying (GE) in CVS patients. Material and Methods This was a retrospective study of 30 adult patients who met Rome III diagnostic criteria for CVS. Rapid GE was defined using two different predefined criteria as either <50% isotope retention or <65% isotope retention at 1st hour and/or <20% at 2nd hour. Results Of the 30 patients (25 had 4-hr GE) diagnosed with CVS, 22 were females and 8 males with a mean age of 39 years. Overall, 20 (80%) of the 25 CVS patients met the predefined criteria of <50% retention for rapid GE in the first hour. Fifteen (60%) met the 2-hour criteria for rapid emptying of <20% retention. Five (16.6%) patients of the 25 had a normal GE with a mean retention at the first hour of 65% (52-78%). Nine (36%) also met another predefined criteria of <35% retention for rapid GE in the first hour. Sixteen (64%) met criteria for normal GE. Conclusions (1) In adult CVS patients, GE is either rapid or normal, clearly distinguishing this entity from gastroparesis. (2) Cyclic vomiting syndrome is an important new etiology to explain the finding of rapid GE on a radionuclide test. (3) We suggest that rapid gastric emptying should be added as supportive criteria for diagnosing CVS in adults.
    Medical science monitor: international medical journal of experimental and clinical research 01/2014; 20:1491-5. · 1.22 Impact Factor
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    ABSTRACT: IMPORTANCE Gastroparesis remains a challenging syndrome to manage, with few effective treatments and a lack of rigorously controlled trials. Tricyclic antidepressants are often used to treat refractory symptoms of nausea, vomiting, and abdominal pain. Evidence from well-designed studies for this use is lacking. OBJECTIVE To determine whether treatment with nortriptyline results in symptomatic improvement in patients with idiopathic gastroparesis. DESIGN, SETTING, AND PARTICIPANTS The NORIG (Nortriptyline for Idiopathic Gastroparesis) trial, a 15-week multicenter, parallel-group, placebo-controlled, double-masked, randomized clinical trial from the National Institute of Diabetes and Digestive and Kidney Diseases Gastroparesis Clinical Research Consortium (GpCRC), comparing nortriptyline with placebo for symptomatic relief in idiopathic gastroparesis. One hundred thirty patients with idiopathic gastroparesis were enrolled between March 2009 and June 2012 at 7 US academic medical centers. Patient follow-up was completed in October 2012. Inclusion criteria included delayed gastric emptying and moderate to severe symptom scores using the Gastroparesis Cardinal Symptom Index (GCSI). INTERVENTIONS Nortriptyline vs placebo. Study drug dose was increased at 3-week intervals (10, 25, 50, 75 mg) up to 75 mg at 12 weeks. MAIN OUTCOMES AND MEASURES The primary outcome measure of symptomatic improvement was a decrease from the patient's baseline GCSI score of at least 50% on 2 consecutive 3-week GCSI assessments during 15 weeks of treatment. RESULTS The primary symptomatic improvement outcome did not differ between 65 patients randomized to nortriptyline vs 65 patients randomized to placebo: 15 (23% [95% CI, 14%-35%]) in the nortriptyline group vs 14 (21% [95% CI, 12%-34%]) in the placebo group (P = .86). Treatment was stopped more often in the nortriptyline group (19 [29% {95% CI, 19%-42%}]) than in the placebo group (6 [9%] {95% CI, 3%-19%}]) (P = .007), but numbers of adverse events were not different (27 [95% CI, 18-39] vs 28 [95% CI, 19-40]) (P = .89). CONCLUSIONS AND RELEVANCE Among patients with idiopathic gastroparesis, the use of nortriptyline compared with placebo for 15 weeks did not result in improvement in overall symptoms. These findings do not support the use of nortriptyline for idiopathic gastroparesis. TRIAL REGISTRATION clinicaltrials.gov Identifier: NCT00765895.
    JAMA The Journal of the American Medical Association 12/2013; 310(24):2640-9. · 29.98 Impact Factor
  • Mohammad Bashashati, Richard W McCallum
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    ABSTRACT: Nausea and vomiting are common gastrointestinal complaints which could be triggered by stimuli in both the peripheral and central nervous systems. They may be considered as defense mechanisms when threatening toxins/agents enter the gastrointestinal tract or there is excessive retention of gastrointestinal contents due to obstruction. The pathophysiology of nausea and vomiting is complex and much still remains unknown. Therefore, treatments are restricted or ineffective in many cases. Nausea and vomiting with functional etiologies including cyclic vomiting syndrome are challenging in gastroenterology. In this article, we review potential pathways, neurochemical transmitters, and their receptors which are possibly involved in the pathophysiology of nausea and vomiting including the entity cyclic vomiting syndrome.
    European journal of pharmacology 10/2013; · 2.59 Impact Factor
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    ABSTRACT: The following paper on gastroesophageal reflux disease (GERD) and Barrett's esophagus (BE) includes commentaries on defining esophageal landmarks; new techniques for evaluating upper esophageal sphincter (UES) tone; differential diagnosis of GERD, BE, and hiatal hernia (HH); the use of high-resolution manometry for evaluation of reflux; the role of fundic relaxation in reflux; the use of 24-h esophageal pH-impedance testing in differentiating acid from nonacid reflux and its potential inclusion in future Rome criteria; classification of endoscopic findings in GERD; the search for the cell origin that generates BE; and the relationship between BE, Barrett's carcinoma, and obesity.
    Annals of the New York Academy of Sciences 10/2013; 1300(1):278-295. · 4.38 Impact Factor
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    ABSTRACT: This paper presents commentaries on whether Starling's law applies to the esophagus; whether erythromycin affects esophageal motility; the relationship between hypertensive lower esophageal sphincter and vigorous achalasia; whether ethnic- and gender-based norms affect diagnosis and treatment of esophageal motor disorders; health care and epidemiology of chest pain; whether normal pH excludes esophageal pain; the role of high-resolution manometry in noncardiac chest pain; whether pH-impedance should be included in the evaluation of noncardiac chest pain; whether there are there alternative therapeutic options to PPI for treating noncardiac chest pain; and the usefulness of psychological treatment and alternative medicine in noncardiac chest pain.
    Annals of the New York Academy of Sciences 10/2013; 1300(1):96-109. · 4.38 Impact Factor
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    ABSTRACT: Gastric electrical stimulation (GES) is a therapeutic option for intractable symptoms of gastroparesis (GP). Idiopathic GP (ID-GP) represents a subset of GP. A prospective, multicenter, double-blinded, randomized, crossover study to evaluate the safety and efficacy of Enterra GES in the treatment of chronic vomiting in ID-GP. Thirty-two ID-GP subjects (mean age 39; 81% F, mean 7.7 years of GP) were implanted with GES. The stimulator was turned ON for 1½ months followed by double-blind randomization to consecutive 3-month crossover periods with the device either ON or OFF. ON stimulation was followed in unblinded fashion for another 4.5 months. Twenty-five subjects completed the crossover phase and 21 finished 1 year of follow-up. During the unblinded ON period, there was a reduction in weekly vomiting frequency (WVF) from baseline (61.2%, P < 0.001). There was a non-significant reduction in WVF between ON vs OFF periods (the primary outcome) with median reduction of 17% (P > 0.10). Seventy-five percent of patients preferred the ON vs OFF period (P = 0.021). At 1 year, WVF remained decreased (median reduction = 87%, P < 0.001), accompanied by improvements in GP symptoms, gastric emptying and days of hospitalization (P < 0.05). (i) In this prospective study of Enterra GES for ID-GP, there was a reduction in vomiting during the initial ON period; (ii) The double-blind 3-month periods showed a non-significant reduction in vomiting in the ON vs OFF period, the primary outcome variable; (iii) At 12 months with ON stimulation, there was a sustained decrease in vomiting and days of hospitalizations.
    Neurogastroenterology and Motility 07/2013; · 2.94 Impact Factor
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    ABSTRACT: TZP-102, a potent, oral, ghrelin receptor agonist, improved diabetic gastroparesis symptoms in Phase 2a. Patients with type 1 or 2 diabetes, delayed gastric half-emptying (T1/2 ), and ≥3 months gastroparesis symptoms randomized 1 : 1 : 1 to double-blind placebo, 10-mg, or 20-mg TZP-102 once daily for 12 weeks (Study TZP-102-CL-G003). Study TZP-102-CL-G004 patients randomized 1 : 1 to 10-mg TZP-102:placebo three-times-daily. Primary endpoint was change-from-baseline through Weeks 11-12 in Daily Diary of Gastroparesis Symptoms Questionnaire (GSDD) via electronic Patient Recorded Outcome device: worst severity of nausea, early satiety, bloating, and upper abdominal pain in 24 h (0 = none-to-5 = very severe). GSDD Composite Score for eligibility was ≥2.5 (Day-14-to-baseline). Patient Overall Treatment Evaluation (OTE) provided an anchor-based minimal clinically important difference (MCID) for GSDD Composite Score. Study TZP-102-CL-G003 enrolled 201 outpatients: females 72%; Caucasians 87%; type 2 diabetes 61%; insulin-dependent 65%; age mean ± SD 53 ± 11.3 years; HbA1c 7.8 ± 1.5%; GCSI 3.4 ± 0.7; GSDD Composite 3.6 ± 0.6; gastric T1/2 131 ± 32 min; n = 69 (10-mg), n = 66 (20-mg), n = 66 (placebo). Primary endpoint (GSDD): significant improvement in all arms, although not for TZP-102 vs placebo: mean change-from-baseline -1.7, -1.4, -1.5 (10-mg, 20-mg, placebo); Gastroparesis Cardinal Symptom Index -1.8, -1.6, -1.5, respectively. The OTE (all patients) at Week-12 was: Patient 3.7 ± 3.2 and Physician 3.6 ± 3.0 with median score for both of 5.0 = important on scale of improvement; individual MCID was 1.61 and 0.94 for group analyses, greater than expected. Study TZP-102-CL-G004 with similar demographic/disease characteristics was prematurely terminated for efficacy futility (n = 64 with Week-4 assessments). Efficacy of TZP-102 was not demonstrated compared with placebo in diabetic gastroparesis; however, there was substantial symptom improvement in all arms (ClinicalTrials.gov NCT01452815/NCT01664637).
    Neurogastroenterology and Motility 07/2013; · 2.94 Impact Factor
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    ABSTRACT: : Nutcracker esophagus is an esophageal motility disorder characterized by the presence of hypertensive contraction waves. These waves can have very high amplitudes, but they maintain a peristaltic pattern and therefore, bolus passage is minimally affected. Esophageal food impactions are rare in nutcracker esophagus. Our patient was a previously asymptomatic man who presented with an esophageal meat impaction due to nutcracker esophagus in which high-resolution manometry played a key role in the diagnosis. Although a rare etiology, nutcracker esophagus can result in esophageal food impaction. High-resolution manometry plays a critical role in the diagnosis of specific motility disorders, even in the setting of minimal symptoms.
    The American Journal of the Medical Sciences 05/2013; · 1.52 Impact Factor
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    ABSTRACT: BACKGROUND: Many patients with gastroparesis have had their gallbladders removed. AIM: To determine if clinical presentations of patients with gastroparesis differ in those with prior cholecystectomy compared to patients who have not had their gallbladder removed. METHODS: Gastroparetic patients were prospectively enrolled in the NIDDK Gastroparesis Registry. Detailed history and physical examinations were performed; patients filled out questionnaires including patient assessment of GI symptoms. RESULTS: Of 391 subjects with diabetic or idiopathic gastroparesis (IG), 142 (36 %) had a prior cholecystectomy at the time of enrollment. Patients with prior cholecystectomy were more often female, older, married, and overweight or obese. Cholecystectomy had been performed in 27/59 (46 %) of T2DM compared to 19/78 (24 %) T1DM and 96/254 IG (38 %) (p = 0.03). Patients with cholecystectomy had more comorbidities, particularly chronic fatigue syndrome, fibromyalgia, depression, and anxiety. Postcholecystectomy gastroparesis patients had increased health care utilization, and had a worse quality of life. Independent characteristics associated with prior cholecystectomy included insidious onset (OR = 2.06; p = 0.01), more comorbidities (OR = 1.26; p < 0.001), less severe gastric retention (OR(severe) = 0.68; overall p = 0.03) and more severe symptoms of retching (OR = 1.19; p = 0.02) and upper abdominal pain (OR = 1.21; p = 0.02), less severe constipation symptoms (OR = 0.84; p = 0.02), and not classified as having irritable bowel syndrome (OR = 0.51; p = 0.02). Etiology was not independently associated with a prior cholecystectomy. CONCLUSIONS: Symptom profiles in patients with and without cholecystectomy differ: postcholecystectomy gastroparesis patients had more severe upper abdominal pain and retching and less severe constipation. These data suggest that prior cholecystectomy is associated with selected manifestations of gastroparesis.
    Digestive Diseases and Sciences 03/2013; · 2.26 Impact Factor
  • Mohammed Saadi, Richard W McCallum
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    ABSTRACT: Irritable bowel syndrome (IBS) is the most common functional bowel disease that affects up to 15% of the US population. The majority of patients with IBS have significant bloating and gas. Recent evidence is beginning to suggest that patients with IBS may have an alteration in the gastrointestinal flora. Specifically, findings suggest that patients with IBS have excessive bacteria in the small bowel, referred to as bacterial overgrowth. Therefore there may be benefits of antibiotic-based therapies for IBS. Rifaximin is a nonabsorbable antibiotic that demonstrates no clinically relevant bacterial resistance. Some studies have demonstrated the efficacy and durable improvement of IBS symptoms after treatment with rifaximin. In this review we explore the current data showing the association of small intestinal bacterial overgrowth (SIBO) and IBS as well as review the available data on the clinical use of rifaximin in the treatment of SIBO in patients with IBS.
    Therapeutic advances in chronic disease. 03/2013; 4(2):71-5.
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    ABSTRACT: OBJECTIVE:: To determine whether bacterial pathogens can be detected within the diseased submucosal tissues of patients with Crohn's disease by molecular techniques independent of cultural methods. DESIGN:: We designed a quantitative polymerase chain reaction to detect 32 virulence genes and transposons within submucosal tissues of patients with Crohn's disease and controls and compared the microbiome of the submucosa with mucosal bacterial populations. RESULTS:: Within submucosal tissues, the bacterial invasion/adherence genes eaeA and invA were detected in 43% of patients (P=0.01 and 0.008 vs. mucosa and controls, respectively) and the Mycobacterium-specific IS900 and 251F genes detected in 50% of patients (P=0.03 vs. mucosa and controls). These findings were mutually exclusive: invasion/adhesion genes and Mycobacterium-associated transposons were not detected in the same patient. Metagenomic sequencing and quantitative polymerase chain reaction results confirmed effective separation of the submucosal and mucosal microbiome and the existence of a submucosal bacterial population within diseased tissues. CONCLUSIONS:: This study is the first to examine the microbial populations of submucosal tissues during intestinal disease and provide evidence of a distinct submucosal microbiome and biotypes within Crohn's disease. These data suggests that Crohn's disease may not be a single disease, but a spectrum that can be divided into distinct biotypes based on the presence of invasion/adherence genes or Mycobacterium-associated transposons. If corroborated by larger population studies, these findings could revolutionize the diagnosis, management, and treatment of Crohn's disease by the identification of patient biotypes and the application of targeted chemotherapeutic treatments that go beyond supportive in nature.
    Journal of clinical gastroenterology 02/2013; · 2.21 Impact Factor
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    ABSTRACT: BACKGROUND: Factors associated with abdominal pain in gastroparesis are incompletely evaluated and comparisons of pain vs other symptoms are limited. This study related pain to clinical factors in gastroparesis and contrasted pain/discomfort- with nausea/vomiting-predominant disease. METHODS: Clinical and scintigraphy data were compared in 393 patients from seven centers of the NIDDK Gastroparesis Clinical Research Consortium with moderate-severe (Patient Assessment of Upper Gastrointestinal Disorders Symptoms [PAGI-SYM] score ≥3) vs none-mild (PAGI-SYM < 3) upper abdominal pain and predominant pain/discomfort vs nausea/vomiting. KEY RESULTS: Upper abdominal pain was moderate-severe in 261 (66%). Pain/discomfort was predominant in 81 (21%); nausea/vomiting was predominant in 172 (44%). Moderate-severe pain was more prevalent with idiopathic gastroparesis and with lack of infectious prodrome (P ≤ 0.05) and correlated with scores for nausea/vomiting, bloating, lower abdominal pain/discomfort, bowel disturbances, and opiate and antiemetic use (P < 0.05), but not gastric emptying or diabetic neuropathy or control. Gastroparesis severity, quality of life, and depression and anxiety were worse with moderate-severe pain (P ≤ 0.008). Factors associated with moderate-severe pain were similar in diabetic and idiopathic gastroparesis. Compared to predominant nausea/vomiting, predominant pain/discomfort was associated with impaired quality of life, greater opiate, and less antiemetic use (P < 0.01), but similar severity and gastric retention. CONCLUSIONS & INFERENCES: Moderate-severe abdominal pain is prevalent in gastroparesis, impairs quality of life, and is associated with idiopathic etiology, lack of infectious prodrome, and opiate use. Pain is predominant in one fifth of gastroparetics. Predominant pain has at least as great an impact on disease severity and quality of life as predominant nausea/vomiting.
    Neurogastroenterology and Motility 02/2013; · 2.94 Impact Factor
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    ABSTRACT: Patient: Female, 25 Final Diagnosis: Rumination syndrome Symptoms: Diarrhea • nausea • vomiting Medication: - Clinical Procedure: - Specialty: Psychology. Rare disease. Rumination syndrome is a behavioral disorder that consists of an effortless regurgitation of undigested food that is subsequently either re-swallowed or ejected within minutes of meal ingestion occurring with liquids and solids. It was first described in children that are mentally disadvantaged but has gained more attention to also occur among both adolescents and adults of normal mental capacity. The prevalence has never accurately been assessed due to its rarity and frequent misdiagnosis. A 25-year-old Caucasian female presented to our care with a chronic history of nausea, vomiting and diarrhea. She has vomited during the postprandial period for the last four years. She also has much as ten bouts of diarrhea per day. There is no definitive evidence of chronic laxative use or self-induced vomiting. Physical examination had no significant findings except a cachectic female patient with a BMI of 16 and hypotension. Patient was eventually discharged home with nutrition recommendations for nocturnal psychology follow up for relaxation behavioral techniques. Due to its elusiveness rumination syndrome is both underdiagnosed and a misdiagnosed condition. One of the reasons for a delayed diagnosis in patients with rumination syndrome is that many physicians are unaware of it, or are even reluctant to make this diagnosis as it could easily be confused with an eating disorder or with other gastrointestinal motility disorders. Because this syndrome may be left undiagnosed for months to years, patients often undergo many expensive and invasive procedures.
    The American journal of case reports. 01/2013; 14:449-52.

Publication Stats

9k Citations
2,765.05 Total Impact Points


  • 2009–2014
    • Texas Tech University Health Sciences Center
      • • Department of Internal Medicine
      • • Department of Medicine
      El Paso, Texas, United States
    • Children's Hospital Los Angeles
      • Division of Medical Genetics
      Los Angeles, California, United States
    • Concordia University–Ann Arbor
      Ann Arbor, Michigan, United States
    • Louisiana State University Health Sciences Center New Orleans
      • Department of Pediatrics
      New Orleans, LA, United States
    • University of Iowa
      Iowa City, Iowa, United States
  • 2013
    • Texas Tech University
      Lubbock, Texas, United States
    • The University of Calgary
      • Department of Physiology and Pharmacology
      Calgary, Alberta, Canada
  • 2010–2013
    • Temple University
      • • Section of Gastroenterology
      • • Department of Medicine
      Philadelphia, PA, United States
    • Aarhus University
      Aarhus, Central Jutland, Denmark
  • 2009–2013
    • University of Texas at El Paso
      El Paso, Texas, United States
  • 2012
    • Northwestern University
      Evanston, Illinois, United States
    • William Beaumont Army Medical Center
      El Paso, Texas, United States
  • 1997–2012
    • Kansas City VA Medical Center
      Kansas City, Missouri, United States
  • 2011
    • University of Louisville
      • Division of Gastroenterology, Hepatology and Nutrition
      Louisville, KY, United States
  • 1997–2011
    • Kansas City University of Medicine and Biosciences
      • • Department of Neurology
      • • Department of Surgery
      Kansas City, Missouri, United States
  • 2008–2009
    • University of Michigan
      • • Department of Internal Medicine
      • • Division of Gastroenterology
      Ann Arbor, MI, United States
    • Hackensack University Medical Center
      Hackensack, New Jersey, United States
  • 2006–2009
    • Children's Mercy Hospitals and Clinics
      Kansas City, Missouri, United States
  • 2002–2009
    • University of Kansas
      • Department of Surgery
      Lawrence, Kansas, United States
  • 2006–2008
    • Children's Mercy Hospitals and Clinics
      Kansas City, Missouri, United States
  • 2005
    • Dalian University of Technology
      • School of Electronic and Information Engineering
      Dalian, Liaoning, China
    • Children's Mercy Hospital
      Kansas City, Missouri, United States
  • 2000
    • Texas A&M University - Galveston
      Galveston, Texas, United States
    • Florida Atlantic University
      • Center for Complex Systems and Brain Sciences
      Boca Raton, FL, United States
  • 1984–1999
    • Yale-New Haven Hospital
      New Haven, Connecticut, United States
  • 1986–1997
    • University of Virginia
      • • Department of Medicine
      • • Division of Maternal Fetal Medicine
      Charlottesville, VA, United States
  • 1995
    • St. Mary Medical Center
      Long Beach, California, United States
  • 1980–1989
    • Yale University
      • Department of Internal Medicine
      New Haven, CT, United States