Brain networks underlying perceptual habituation to repeated aversive visceral stimuli in patients with irritable bowel syndrome.

Patients with irritable bowel syndrome (IBS) show decreased discomfort and pain thresholds to visceral stimuli, as well hypervigilance to gastrointestinal sensations, symptoms, and the context in which these visceral sensations and symptoms occur. Previous research demonstrated normalization of visceral hypersensitivity following repeated exposure to experimental rectal stimuli over a 12-month period that was associated with reduction in cortical regions functionally associated with attention and arousal. Building upon these functional analyses, multivariate functional and effective connectivity analyses were applied to [(15)O] water positron emission tomography (PET) data from 12 IBS patients (male=4) participating in a PET study before and after 4 visceral sensory testing sessions involving rectal balloon distensions over a 1-year period. First, behavioral partial least squares was applied to test for networks related to reduced subjective ratings observed following repeated application of an aversive rectal stimulus. Next, path analysis within a structural equation modeling framework tested the hypothesis that perceptual habituation to the repeated visceral stimuli resulted in part from the reduced connectivity within a selective attention to threat network over time. Two independent, perception-related networks comprised of interoceptive, attentional and arousal regions were engaged differentially during expectation and distension. In addition, changes in the effective connectivity of an attentional network as well as modulatory amygdala influence suggested that perceptual habituation associated with repeated stimulus delivery results both in an increase in top-down modulation of attentional circuits, as well as in a reduction of amygdala-related interference with attentional mechanisms.

Longitudinal change in perceptual and brain activation response to visceral stimuli in irritable bowel syndrome patients.

BACKGROUND & AIMS: Symptom-related fears and associated hypervigilance toward visceral stimuli may play a role in central pain amplification and irritable bowel syndrome (IBS) pathophysiology. Repeated stimulus exposure leads to decreased salience of threat and reduction of hypervigilance. We sought to evaluate hypervigilance in IBS visceral hypersensitivity and associated brain activity. METHODS: Twenty IBS patients (14 female; moderate to severe symptoms) and 14 healthy controls participated in symptom and rectal distention assessments 6 times over 12 months. In a subset of 12 IBS patients, H2 15O-positron emission tomography images were obtained during baseline, rectal distentions, and anticipation of an aversive distention during the first and last session. Statistical parametric mapping (SPM99) was used to identify areas and networks activated during each session as well as those with differential activation across the 2 sessions. RESULTS: Perceptual ratings of the rectal inflations normalized over 12 months, whereas IBS symptom severity did not. There were no sex-related differences in these response patterns. Stable activation of the central pain matrix was observed over 12 months, and activity in limbic, paralimbic, and pontine regions decreased. During the anticipation condition, there were significant decreases in amygdala, dorsal anterior cingulate cortex, and dorsal brainstem activation at 12 months. Covariance analysis supported the hypothesis of changes in an arousal network including limbic, pontine, and cortical areas underlying the decreased perception seen over the multiple stimulations. CONCLUSIONS: In IBS patients, repeated exposure to experimental aversive visceral stimuli results in the habituation of visceral perception and central arousal, despite stable activation of networks processing visceral pain and its anticipation.

Utilization and costs for children who have special health care needs and are enrolled in a hospital-based comprehensive primary care clinic.

OBJECTIVE: When deciding how much hospital resources should be allocated to comprehensive primary care clinics for children with multisystem disorders, it is important to consider all of the non-primary care revenue streams associated with these children as well as the effects of a comprehensive primary care program on access and quality. The objectives of this study were, first, to determine costs as well as the payments associated with hospital ambulatory and inpatient services for children with multisystem disorders followed by a comprehensive primary care clinic; and, second, to determine the effect of enrollment in a hospital-based comprehensive primary care clinic on ambulatory and inpatient utilization patterns and expenditures for children with multisystem disorders. METHODS: The study population for the payment analysis consisted of 1012 children of all ages who were seen in the Special Primary Care Clinic (SPCC) in 2001. For these children, outcomes included direct costs, total (direct plus allocated overhead) costs, and payments per patient per 365 days after their first SPCC visit in 2001. A total of 175 of these patients were 4 years of age or older and had no SPCC visit before their first visit in 2001. We compared utilization and expenditures for the 175 children during the year before enrollment in SPCC with those in the year after enrollment. The Children's Hospital administrative database was used to document direct costs, total costs, and payments by type of service for 365 days after an index visit. Ambulatory services included medical and surgical ambulatory, inpatient, emergency department (ED), and ancillary services. We determined the proportion of children who had visits; the visit rates per 100 child-years; and the average total and direct costs per visit, per child with a visit, and per child-year. Inpatient services data included non-intensive care and intensive care hospitalization rates per 100 child-years; the proportion of children hospitalized; their average length of stay; and the average total and direct costs per hospitalization, per patient hospitalized, and per child-year of total patients in the cohort. RESULTS: For 1012 children who were seen in SPCC in 2001, the hospital overall loss per child-year was $956. The loss per child-year for outpatient services was $1554. This loss was partially offset by a gain from inpatient services of $598. For the 175 patients for whom data were available to compare costs before and after enrollment in the SPCC, there were no significant differences in hospitalization or in direct costs per patient for patients who were hospitalized. The average length of non-intensive care stay was lower after enrollment (4.8 vs 11.7). In the surgical specialty analysis, children were more likely to see a surgeon after enrollment (41% vs 21%) and had a higher rate of visits per 100 child-years (102.3 vs 51.4). Differences in medical subspecialty, ancillary, and ED services did not achieve statistical significance. CONCLUSION: This study suggests that children with multisystem disorders are medically fragile and require frequent hospitalizations and ED visits even with improved primary care. Enrollment in a comprehensive primary care program was associated with a decreased length of stay for non-intensive care hospitalizations and with increased use of surgical services.

Sex-based differences in gastrointestinal pain.

Recent interest has focused on sex-related differences in irritable bowel syndrome (IBS) physiology and treatment responsiveness to novel pharmacologic therapies. Similar to a variety of other chronic pain conditions and certain affective disorders, IBS is more prevalent amongst women, both in population-based studies as well as in clinic-based surveys. Non-painful gastrointestinal symptoms, constipation and somatic discomfort are more commonly reported by female IBS patients. While perceptual differences to rectosigmoid stimulation are only observed following repeated noxious stimulation of the gut, sex-related differences in certain sympathetic nervous system (SNS) responses to rectosigmoid stimulation are consistently seen. Consistent with experimental findings in animals, current evidence is consistent with a pathophysiological model which emphasizes sex-related differences in autonomic and antinociceptive responses to certain visceral stimuli.

The neural correlates of placebo effects: a disruption account.

The neurocognitive pathways by which placebo effects operate are poorly understood. Positron emission tomography (PET) imaging was used to assess the brain response of patients with chronic abdominal pain (irritable bowel syndrome; IBS) to induced intestinal discomfort both before and after a 3-week placebo regimen. A daily symptom diary was used to measure symptom improvement. Increases in right ventrolateral prefrontal cortex (RVLPFC) activity from pre- to post-placebo predicted self-reported symptom improvement, and this relationship was mediated by changes in dorsal anterior cingulate (dACC), typically associated with pain unpleasantness. These results are consistent with disruption theory [Lieberman, M.D., 2003. Reflective and reflexive judgment processes: a social cognitive neuroscience approach. In: Forgas, J.P., Williams, K.R., von Hippel, W. (Eds.), Social Judgments: Explicit and Implicit Processes. Cambridge Univ. Press, New York, pp. 44-67], which proposes that activation of prefrontal regions associated with thinking about negative affect can diminish dACC and amygdala reactivity to negative affect stimuli. This is the first study to identify a neural pathway from a region of the brain associated with placebos and affective thought to a region closely linked to the placebo-related outcome of diminished pain unpleasantness.

Sex-related differences in IBS patients: central processing of visceral stimuli.

BACKGROUND & AIMS: Women have a higher prevalence of irritable bowel syndrome (IBS) and possible differences in response to treatment, suggesting sex-related differences in underlying pathophysiology. The aim of this study was to determine possible sex-related differences in brain responses to a visceral and a psychological stressor in IBS. METHODS: Regional cerebral blood flow measurements using H(2)(15)O positron emission tomography were compared across 23 female and 19 male nonconstipated patients with IBS during a visceral stimulus (moderate rectal inflation) and a psychological stimulus (anticipation of a visceral stimulus). RESULTS: In response to the visceral stimulus, women showed greater activation in the ventromedial prefrontal cortex, right anterior cingulate cortex, and left amygdala, whereas men showed greater activation of the right dorsolateral prefrontal cortex, insula, and dorsal pons/periaqueductal gray. Similar differences were observed during the anticipation condition. Men also reported higher arousal and lower fatigue. CONCLUSIONS: Male and female patients with IBS differ in activation of brain networks concerned with cognitive, autonomic, and antinociceptive responses to delivered and anticipated aversive visceral stimuli.

Brain responses to visceral and somatic stimuli in patients with irritable bowel syndrome with and without fibromyalgia.

OBJECTIVE: Symptoms of irritable bowel syndrome (IBS) and fibromyalgia (FM) commonly coexist. We hypothesized that one of the mechanisms underlying this comorbidity is increased activation of brain regions concerned with the processing and modulation of visceral and somatic afferent information, in particular subregions of the anterior cingulate cortex (ACC). METHODS: Regional cerebral blood flow (rCBF) was assessed in age-matched female IBS (n = 10) and IBS + FM (n = 10) subjects using H(2)(15)O positron emission tomography during noxious visceral (rectal) and somatic pressure stimuli. RESULTS: GI symptom severity was significantly higher in the IBS patients compared with the IBS + FM patients (p < 0.05). In addition, IBS + FM patients rated somatic pain as more intense than their abdominal pain (p < 0.05). Whereas the somatic stimulus was less unpleasant than the visceral stimulus for IBS patients without FM, the somatic and visceral stimuli were equally unpleasant in the IBS + FM group. Group differences in regional brain activation were entirely within the middle subregion of the ACC. There was a greater rCBF increase in response to noxious visceral stimuli in IBS patients and to somatic stimuli in IBS + FM patients. CONCLUSION: Chronic stimulus-specific enhancement of ACC responses to sensory stimuli in both syndromes may be associated with cognitive enhancement of either visceral (IBS) or somatic (IBS + FM) sensory input and may play a key pathophysiologic role in these chronic pain syndromes.

Factors that influence the willingness of private primary care pediatricians to accept more Medicaid patients.

OBJECTIVE: State Medicaid programs are obligated by federal law to ensure that enrolled children have access to care and services to the same extent as other children in the same geographic area. Because most children in the United States receive health care from private primary care physicians, participation by private, office-based primary care pediatricians is critical to meeting this equal access obligation. The objective of this study was to document variations in Medicaid participation of private office-based primary care pediatricians across states and to examine the effects of payment levels, prevalence of capitated Medicaid payment, and paperwork concerns on participation. METHODS: Survey data collected from 3773 primary care pediatricians who practice in private office-based settings were analyzed with Medicaid physician payment data from other sources. Univariate analyses and a multiple regression were used to examine the effects of payment level, prevalence of capitated Medicaid payment, and paperwork concerns on private primary care pediatricians' participation in state Medicaid programs. RESULTS: Results revealed substantial state-to-state variation in respondents' participation in Medicaid. Univariate analyses found that participation increased with state Medicaid payment levels but decreased as the proportion of Medicaid enrollees with primary care capitated payments rose and as paperwork concerns increased. With physician workforce held constant, a regression analysis showed that pediatrician participation in Medicaid increased significantly with Medicaid payment but decreased as the proportion of capitated Medicaid patients increased and as paperwork concerns rose. CONCLUSIONS: This study found that low payment, capitation, and paperwork concerns all relate to low Medicaid participation by primary care office-based pediatricians. It behooves state policy makers to address these 3 factors to ensure sufficient primary care physician capacity to serve appropriately children who are enrolled in state Medicaid programs.