The goal of this clinical trial is to learn which treatment is more effective for children with functional constipation (FC) and fecal incontinence (FI), also called retentive encopresis.

Functional constipation is common in children and can cause pain, embarrassment, social stress, and repeated medical visits. One of the hardest symptoms to treat is fecal incontinence. Two common treatments are polyethylene glycol 3350 (PEG), an osmotic laxative, and Senna, a plant-based stimulant laxative. PEG is often used as standard maintenance therapy, while Senna is increasingly used, especially in children with difficult or refractory constipation. However, there is not enough high-quality evidence comparing these two treatments directly in children with fecal incontinence.

The main question this study aims to answer is:

Does Senna reduce the number of fecal incontinence episodes more than PEG after 3 months of treatment? The study will also assess safety, tolerability, abdominal pain or cramping, use of rescue enemas, treatment satisfaction, and treatment compliance.

This is a prospective, randomized, double-blinded clinical trial. Children will be randomly assigned to receive either daily Senna or daily PEG for 3 months. Neither the families nor the treating medical team will know which treatment the child is receiving. Both medications will be prepared as identical-looking white powder in identical packages.

Participants will be children aged 4 to 18 years who have functional constipation according to Rome IV criteria and have fecal incontinence at least 4 times per week. Children with an organic disease that may cause fecal incontinence, such as Hirschsprung disease, spinal cord abnormalities, or anorectal malformations, will not be included.

Before starting the study medication, all participants will complete a 3-day bowel clean-out using high-dose PEG, with Pico-Salax added on the third day. After this clean-out, children will start their assigned daily treatment, either Senna or PEG. The dose will be based on age and may be adjusted by the physician according to stool consistency, stool frequency, cramping, and the child's clinical response. All families will also receive behavioral advice, including regular toilet sitting twice daily, correct toilet position using a footstool, and going to the toilet when the child feels the need.

Participants will:

• Take daily Senna or daily PEG for 3 months
• Visit the clinic at baseline, 1 month, 2 months, and 3 months
• Complete a 7-day stool and fecal incontinence diary before each visit
• Report abdominal pain, cramping, diarrhea, perianal irritation, or any other adverse events
• Return medication containers so compliance can be checked by weighing the remaining medication
• Complete satisfaction and improvement questionnaires at the 3-month visit

Outcome Measurements:

The primary outcome is the mean number of fecal incontinence episodes per week after 3 months of treatment. This will be measured using a prospective 7-day diary completed by the family before the 3-month clinic visit.

The secondary outcomes, assessed at 3 months, include:

• Change in patient-initiated toilet sitting, meaning times when the child independently says they need to defecate
• The proportion of children who reach 0-1 fecal incontinence episodes per week
• The proportion of children with any improvement, defined as at least 1 fewer fecal incontinence episode per week
• Number of rescue enemas used during the 3-month study period
• Frequency and severity of abdominal pain or cramping
• Parent-reported satisfaction with treatment using a 5-point Likert scale
• Family impression of overall improvement using a 5-point Likert scale
• The proportion of children still meeting Rome IV criteria for functional constipation
• Treatment compliance, defined as good compliance if more than 80% of doses were taken

The study plans to enroll 80 children total, with 40 children in the Senna group and 40 children in the PEG group.

Inclusion Criteria:

• Children aged 4 to 18 years.
• Diagnosis of functional constipation according to Rome IV criteria.
• Fecal incontinence occurring ≥4 times per week.
• Treatment-naïve or treatment-experienced (i.e., any of the following treatments in the past: PEG, senna, bisacodyl and rectal disimpaction) patients.

Exclusion Criteria:

• Presence of organic disease that causes or contributes to fecal incontinence (e.g., Hirschsprung disease, spinal cord anomalies, anorectal malformations).