Objectives: This study aims to evaluate the clinical efficacy and safety of repetitive transcranial magnetic stimulation (rTMS) in patients with diarrhea-predominant irritable bowel syndrome (IBS-D), and to explore the potential underlying mechanisms by which rTMS alleviates clinical symptoms in IBS-D patients.

Design: This is a clinical trial that uses clinical symptom scales to assess the therapeutic effect of rTMS on IBS-D patients. Meanwhile, gut microbiota and metabolite profiling, as well as the methane-hydrogen breath test, will be applied to investigate the mechanism of action from the perspectives of gut microecology, intestinal motility, and metabolism, so as to provide scientific evidence for the clinical application of rTMS in the treatment of IBS-D.

Background: A large number of studies have demonstrated that repetitive transcranial magnetic stimulation (rTMS) can alleviate chronic pain. Its potential mechanisms include modulating cortical excitability, improving cerebral blood flow and metabolism, regulating neurotransmitters and gene expression, and inducing neuroplasticity. Previous findings indicate that the gut-brain neural circuit involving the insular cortex and anterior cingulate cortex serves as a key pathway regulating chronic visceral pain in irritable bowel syndrome (IBS). Studies have also shown that transcranial magnetic stimulation (TMS) can reduce visceral hypersensitivity in patients with IBS. On this basis, the present study further investigates whether rTMS can improve diarrheal symptoms in patients with diarrhea-predominant irritable bowel syndrome (IBS-D), in order to provide a more reliable and effective therapeutic strategy for clinical practice.

Objectives:

This study aims to evaluate the overall clinical efficacy of rTMS in the treatment of IBS-D, including diarrhea, abdominal pain, quality of life, psychiatric symptoms (anxiety and depression), and sleep disturbance. Meanwhile, the underlying mechanisms of rTMS will be explored using gut microbiota and metabolomic profiling, as well as the methane-hydrogen breath test.

Methods:

This is a clinical trial designed to evaluate the efficacy of rTMS in treating chronic diarrhea in IBS-D patients. A total of 46 IBS-D patients meeting eligibility criteria will be randomly assigned to receive either real rTMS (n=23) or sham rTMS (n=23).

The treatment will last for 3 weeks. The real rTMS group will receive 1 Hz stimulation, 20 minutes per session. The sham rTMS group will receive 0 Hz stimulation (sham condition), 20 minutes per session.

Low-frequency rTMS (1 Hz) will be applied over the medial prefrontal cortex (mPFC) using a magnetic stimulator manufactured by Wuhan IRide Company. Stimulation intensity will be set at 80% of the resting motor threshold (RMT). RMT is defined as the minimal stimulus intensity required to evoke a motor evoked potential (MEP) amplitude of ≥50 μV in at least 5 out of 10 consecutive trials.

The coil will be placed tangentially over the mPFC. Patients will remain seated quietly with minimal head movement during the entire session.For the real rTMS group: 1 Hz frequency, 80% RMT intensity, 1100 pulses per session, with each pulse train lasting 2 seconds, and a total session duration of 20 minutes.For the sham rTMS group: the coil is positioned identically but without effective magnetic stimulation, while pre-recorded sound is played to mimic the acoustic feedback of real rTMS.

Outcome Assessments:

Clinical assessments will include diarrhea, abdominal pain, quality of life, intestinal sensitivity, mood status, and sleep.

Mechanistic evaluations will be performed using gut microbiota and metabolite analysis, combined with methane-hydrogen breath test, to explore the mechanisms underlying rTMS effects on chronic diarrhea in IBS-D patients.

Gut microbiota data will be analyzed to compare differences between the treatment and control groups before and after intervention. Correlation analyses will be conducted between clinical improvement and changes in microbial and metabolic profiles.

Inclusion Criteria:

Eligible participants had to be between 18- 60 years of age and fulfill the Rome IV criteria for IBS-D. Specifically, patients must have experienced recurrent abdominal pain at least one day per week in the last three months, with symptom onset at least six months prior to diagnosis, associated with defecation or a change in the frequency or form (appearance) of stool. More than 25% of stool episodes be classified as Bristol Stool Form Scale (BSFS) type 6 or 7, and fewer than 25% as type 1 or 2. In addition, patients were required to exhibit moderate to severe symptoms, defined as an Irritable Bowel Syndrome Symptom Severity Scale (IBS-SSS) score greater than 175 (on a 500-point scale). Dietary preferences of all participants included non vegetarian options and participants maintain stable dietary habits for at least one month prior to randomization. Moreover, patients aged over 50 were required to provide documentation of a normal colonoscopy performed within the preceding three years.

Exclusion Criteria:

The exclusion criteria included a completion rate of daily diaries of less than 50% during the screening period, a history of organic gastrointestinal disease, such as inflammatory bowel disease, a history of surgical resection of the GI tract or cholecystectomy, a recent diagnosis of Helicobacter pylori infection within the past 2 years, a history of gluten or lactose intolerance, a history of malignancy, or a history of neurological or psychiatric conditions. Additionally, individuals with severe systemic diseases, including uncontrolled diabetes mellitus, hyperthyroidism, or severe hepatic, renal, or cardiac insufficiency, were excluded. The use of probiotic or prebiotic supplements, antibiotics (including rifaximin), prokinetic or antidiarrheal agents, tricyclic antidepressants, or immunosuppressive therapies was not permitted within 4 wk prior to screening. Prohibited conditions during the study period included pregnancy, lactation, or being within 12 months postpartum. Lastly, participants with severe needle phobia, metal allergies, implanted cardiac pacemakers, or a known allergic diathesis were excluded. All participants provided their voluntary, written, informed consent prior to their inclusion.