Functional gastrointestinal disorders, also known as disorders of gut-brain interaction, is common among adult population in Hong Kong. An overview on the bidirectional interaction between brain and gut, etiology and treatment for these disorders, together with the discussion of the role of inflammation in neuropsychiatric disorders with a perspective from traditional Chinese Medicine were discussed in the Joint Symposium of the Hong Kong Society of Gastrointestinal Motility and the Hong Kong Society of Biological Psychiatry.
Professor Wu spoke about functional GI disorders (FGIDs) which are chronic recurrent digestive problems with no structural abnormalities. Examples include functional dyspepsia (FD) and irritable bowel syndrome (IBS) which are common in Hong Kong and affect approximately one-fifth of the adult Hong Kong population.
“Functional gastrointestinal disorders (FGIDs) are also called disorders of gut-brain interaction (DGBI). About one-third of the general population and over 80% of patients have psychiatric comorbidity” - Prof Justin Wu
FGIDs are also called disorders of gut-brain interaction (DGBI) and are often characterized by visceral hypersensitivity and GI motility dysfunction. About one-third of the general population and over 80% of patients in referral centers have psychiatric comorbidity. Symptoms include serotonin hyper-responsiveness, increased cortisol levels and immune activation with diet as trigger and gut microbiota disruption. FGID is also associated with GAD (generalized anxiety disorder) and depression in community and referral center patients. Links between psychological comorbidity and FGID include a history of abuse and early life adversity, anxiety disorder, increased hypothalamic-pituitary-adrenal (HPA) axis and serotonin responsiveness, as well as specific G-protein β3 subunit/serotonin transporter (SERT) gene polymorphisms.
“Selective serotonin reuptake inhibitors (SSRIs) are also effective for irritable bowel syndrome and refractory functional dyspepsia with associated drop in anxiety scores.” - Prof Justin Wu
Considering the links between brain and gut, to what extent is an irritable bowel a reflection of an irritable brain? Professor Wu cited reports which show no difference in visceral afferent processing but aberrant brain processing instead. This, in turn, is associated with changes in emotional arousal and endogenous pain modulation. Psychological stress may be the primary event for both immune activation and GI symptoms, with increases in IL-6 and TNF-α. Tricyclic antidepressants (TCAs) reduce stress-induced visceral hypersensitivity and may be suitable for refractory functional dyspepsia. Imipramine, for example, was found to be effective in 63.6 % of patients with refractory functional dyspepsia (compared to 36.5% improvement in placebo-treated subjects). Selective serotonin reuptake inhibitors (SSRIs) are also effective for irritable bowel syndrome and refractory functional dyspepsia with associated drop in anxiety scores, but Professor Wu noted that some patients need withdrawal or dose adjustment due to adverse side effects.
“TCAs were found to work better in patients without depression or anxiety while SSRIs were better for patients with anxiety or depression” - Prof Justin Wu
In discussing the use of antidepressants for FGIDs, there was interest in whether the mechanisms of action were mainly anti-anxiety, antidepressant-like or direct GI effects. Professor Tang mentioned the chicken and egg question and preferred an integrated approach not separated into components. A healthy gut is associated with a healthy brain synapse and vice-versa. Professor Wu cited a recent clinical trial which studied placebo versus TCAs or SSRIs in functional dyspepsia patients. TCAs were found to work better in patients without depression or anxiety while SSRIs were better for patients with anxiety or depression. When compared, SSRIs were not as useful for normalizing peripheral visceral sensations. For disorders outside the FGID group such as autism and epilepsy, research findings are still early. It is possible that once a condition such as autism has formed, it may be hard to reverse. Currently probiotics for autism are not approved by NIH in the USA.