What is the study about? This study is for adults with diarrhea-predominant irritable bowel syndrome (IBS-D) who suffer from chronic visceral pain. We aim to investigate whether combining two different treatment approaches is more effective in alleviating IBS-D symptoms than either treatment alone. The first treatment is a non-invasive brain stimulation technique called repetitive Transcranial Magnetic Stimulation (rTMS), while the second treatment involves either an intestinal antispasmodic medication (Pinaverium Bromide) or a probiotic (Bifidobacterium).

What will participants do?

Participants will be randomly assigned by a computer to one of four groups:

1. Group 1: Receive real rTMS sessions + take Pinaverium Bromide pills.
2. Group 2: Receive real rTMS sessions + take Bifidobacterium pills.
3. Group 3: Receive fake (sham) rTMS sessions + take Pinaverium Bromide pills.
4. Group 4: Receive fake (sham) rTMS sessions + take Bifidobacterium pills.

Neither the participant nor the doctor giving the treatments will know which group the participant is in for the rTMS part (this is called "blinding"). The study will involve several weeks of treatment and follow-up visits to track symptoms.

What are the potential benefits and risks? Potential Benefits: Participants may experience a reduction in their abdominal pain, diarrhea, and other IBS symptoms. However, benefit cannot be guaranteed. The information from this study may help other IBS patients in the future.

Potential Risks: rTMS is generally safe but may cause mild headache, scalp discomfort, or lightheadedness. The medications may have side effects like any drug, which will be explained in detail before the study starts.

Why is this study important? This is the first study to test how brain stimulation and gut-focused treatments work together for IBS pain. The results could lead to new and more effective combination therapies for people who don't get enough relief from current treatments.

This is a multicenter, randomized, double-blind, sham-controlled, 2x2 factorial trial investigating the efficacy of combining repetitive Transcranial Magnetic Stimulation (rTMS) with gut-directed therapy for chronic visceral pain in diarrhea-predominant irritable bowel syndrome (IBS-D).

Scientific rationale: Current treatments for IBS-D often provide inadequate relief. rTMS, a non-invasive neuromodulation technique, may alleviate pain by restoring cortical excitability and neural plasticity. Its potential synergy with gut-targeted agents (antispasmodic or probiotic) remains unexplored.

Objectives: The primary objective is to determine the interaction effect between rTMS (real vs. sham) and drug (pinaverium bromide vs. bifidobacterium) on the composite response rate at Week 2. Secondary objectives include assessing changes in IBS-SSS, IBS-QoL, PHQ-9 scores, and anorectal manometry parameters.

Methodology: 140 eligible adults will be randomized equally into four groups: (1) real rTMS + pinaverium bromide, (2) real rTMS + bifidobacterium, (3) sham rTMS + pinaverium bromide, (4) sham rTMS + bifidobacterium. Real rTMS will be delivered at 1Hz, 80% MT over the mPFC for 20 minutes daily for 2 weeks. Sham rTMS uses a placebo coil. Pinaverium bromide (50mg tid) and bifidobacterium (500mg bid) will be administered with matched placebos to maintain blinding. Participants, outcome assessors, and statisticians will be blinded to intervention assignments.

Outcomes: The primary outcome is the proportion of participants achieving composite response (≥30% reduction in worst abdominal pain AND ≥50% reduction in days with BSFS 6/7 stools) at Week 2. Secondary outcomes include changes from baseline in IBS-SSS, IBS-QoL, PHQ-9, and manometry measures.

Statistics: A factorial ANOVA will be used to test the main and interaction effects. The primary analysis will follow the intention-to-treat principle.

Inclusion Criteria:

(I)Age range 18-75 years (either sex) (II)Fulfilling the Rome IV criteria for irritable bowel syndrome diagnosis (III)Bristol stool type 6-7 in >25% and type 1-2 in <25% of bowel movements (IV)Patients experienced Bristol stool type 6 or 7 on ≥4 days with mean abdominal pain score ≥3 during the initial 2-week period

Exclusion Criteria:

(I)Documented organic gastrointestinal pathology; endocrinologic or metabolic diseases with known gastrointestinal motility effects including diabetes mellitus and hyperthyroidism; previous surgical interventions involving abdominal cavity intestinal tract or anal region (II)current use of any medication with documented effects on gastrointestinal motility or secretory function; administration of concurrent therapies or pharmacologic agents capable of confounding treatment efficacy or safety evaluations (III)pregnancy lactation or postpartum status within 12 months (IV)noncompliance with randomized treatment allocation or demonstrated poor adherence tendencies

An independent researcher will generate a randomized sequence using an online tool (https://www.sealedenvelope.com/simple-randomiser/v1/lists) with 1:1:1:1 allocation stratified by center. The attending physician will open sealed envelopes before treatment to assign participants to one of four groups: rTMS with pinaverium, rTMS with Bifidobacterium, sham with pinaverium, or sham with Bifidobacterium. Block randomization (block size=4) ensures balance across centers.

For blinding, identical capsules conceal medications from patients and outcome assessors. Participants are blinded to real/sham rTMS due to identical auditory cues. rTMS operators are unblinded but excluded from outcome assessment. All other personnel remain blinded.