Irritable bowel syndrome: analyzing the brain-gut axis and efficacy of psychological treatment
MetadataShow full item record
Irritable bowel syndrome (IBS) is the most common chronic functional gastrointestinal disorder that affects approximately 11% of the global population with a higher prevalence in women and those under the age of 50. IBS is characterized and diagnosed by the presence of a group of symptoms including abdominal pain, bloating or distension accompanied by altered bowel movements. A positive diagnosis of IBS can be made in the presence of well-defined, validated diagnostic criteria and in addition to the exclusion of organic disease with minimal testing. The lack of specific therapeutic targets makes treatment of IBS very difficult and its management is focused on symptom relief. IBS has a well-established high comorbidity with anxiety, depression, and psychosomatic disorders which contributes significantly to a substantial burden of illness. IBS patients exhibit a markedly decreased quality of life, decreased work productivity and increased absenteeism from work, and increased direct healthcare utilization (such as office visits, medical tests, and specialty referrals), resulting in a large economic burden for society. Despite this, effective pharmacologic and non-pharmacologic treatment options are limited and many patients with IBS do not achieve complete symptom relief long term and continue to suffer from IBS symptoms. Early pioneering in the study of this disease has called for a biopsychosocial model, a model in which psychological and social factors are also considered in IBS treatment. Through consideration of this model, it has been discovered that the disease has strong ties with early life environment, daily stress, and coping skills. Research in the past decades has established IBS as a disease of neurogastroenterology and involves disturbances in the brain-gut axis, the connection between the central nervous system and enteric nervous system. The brain-gut axis is organized in hierarchies with the first control level consisting of the enteric nervous system (ENS) sensory, muscular, and interneurons, all of which form reflex circuitry to control gastrointestinal (GI) motility and sensation among other functions. The central nervous system (CNS) synapses onto these circuits via vagal and spinal afferents. Information from the luminal GI tract is processed in the higher cortical structures of the brain, particularly in the hypothalamus, amygdala, anterior cingulage cortex (ACC) and prefrontal cortex (PFC). These structures are also important for homeostasis and regulation of attention, emotion, and behavior. Disturbances of these pathways result in peripheral and eventually central sensitization, the subject of this thesis. Sensitization in IBS includes visceral hypersensitivity, increased pain perception, and increased GI motility. Due to the cortical regions where this information is processed, these physical symptoms often have a complex interplay with psychological symptoms including anxiety, fear, and stress. The connection between the physical symptoms and psychological symptoms lies in the pain matrix and emotional motor system. This has been confirmed by many brain imaging studies comparing normal individuals with IBS patients testing visceral, somatic and cutaneous pain as well as anxiety and depression levels. IBS patients, unlike control subjects, have been found to have increased pain perception localizing to all these regions and they also rate the pain as more unpleasant, a psychological factor, than normal patients. In addition to increased cortical activation, IBS patients have increased corticotropin releasing factor in the amygdala promoting anxiety and increasing stress levels and GI symptoms. Of note is the fact that stress is both a cause and effect of IBS symptoms and often compounds symptoms due to the cyclical nature of stress and chronic pain. Because stress ties in with both the physical and psychological symptoms faced by IBS patients, implementation of psychological treatment in IBS management is of great importance and have demonstrated improved outcomes in IBS patients. Psychological treatments with empirical evidence are discussed in this thesis and include cognitive behavioral therapy, psychodynamic psychotherapy, hypnotherapy, and mindfulness/relaxation exercises. Whether these all treatments tie into the alterations in cortical processing in brain-gut function is a topic that is yet to be explored.