Constipation in Children

❍ At a glance

• Overflow faecal incontinence - frequent small liquid accidents - is not diarrhoea. It is faecal loading with overflow. Stopping laxatives makes it worse. This distinction is consistently missed.
• Disimpaction must happen before maintenance therapy works. Macrogol (Movicol Paediatric Plain) is the agent of choice: escalate doses over 6-8 days until impaction clears (soft, liquid-ish stools for 24 hours), then drop to maintenance dose.³
• Maintenance treatment should continue for a minimum of 6 weeks after successful bowel habit is established - often 3-6 months or longer. Relapse is common if laxatives are stopped too early. Taper gradually, do not stop abruptly.
• Red flags for organic cause: onset in the first month of life, delayed meconium passage beyond 48 hours (consider Hirschsprung's disease), ribbon stools, failure to thrive, sacral dimple, neurological signs in lower limbs.

❍ Diagnosis and red flags

Functional constipation is a clinical diagnosis using Rome IV criteria: two or more of the following for at least 4 weeks (under 4 years) or at least 2 months (older children): two or fewer defaecations per week; at least one episode per week of incontinence after toilet training; retentive posturing or excessive voluntary stool retention; painful or hard bowel motions; large faecal mass in the rectum; large diameter stools that obstruct the toilet.²

The clinical picture often involves a cycle of painful defaecation leading to stool withholding, harder and larger stools, more pain, and more withholding. Once faecal impaction accumulates in the rectum, overflow incontinence can develop - parents may describe frequent small liquid or paste-like accidents that look like diarrhoea. This is not diarrhoea. Treating it as such (stopping laxatives) makes the underlying constipation worse. The Bristol Stool Chart is a useful objective tool: type 1-2 indicates constipation; type 3-4 is normal; type 5-7 indicates loose stools.

Red flags requiring investigation: onset in the first month of life or delayed meconium passage beyond 48 hours (consider Hirschsprung's disease); ribbon stools; failure to thrive; abdominal distension; sacral dimple or skin changes at the base of the spine (suggest spinal dysraphism); neurological signs in the lower limbs; blood in the stool without a clear anorectal cause.¹ Plain abdominal X-ray is not recommended as a routine tool for diagnosing constipation - clinical assessment is sufficient.

❍ Management: disimpaction and maintenance

Disimpaction first if faecal impaction is present: impaction must be cleared before maintenance laxative treatment is effective. Macrogol (polyethylene glycol with electrolytes) is the agent of choice in NZ. For children aged 1-5 years, start with 2 sachets per day (Movicol Paediatric Plain 13.8 g sachets) and increase by 2 sachets every 2 days up to a maximum of 8 sachets per day, until the impaction clears - indicated by soft, liquid-ish stools for 24 hours.³ Warn parents that high disimpaction doses may produce cramping and watery stools.

Maintenance: once disimpaction is achieved, reduce to a maintenance dose sufficient to produce soft, comfortable stools (Bristol 3-4) once daily. Macrogol is first-line (typically 1 sachet per day in children aged 1-5, adjusted to response). Lactulose is an alternative but less effective and causes more bloating. Stimulant laxatives (senna, bisacodyl) may be added as a second agent if macrogol alone is insufficient. Continue maintenance for a minimum of 6 weeks after successful bowel habit is established, often 3-6 months or longer. Taper the dose gradually rather than stopping abruptly.

Behavioural: regular toilet sits after meals (exploiting the gastrocolic reflex), a footstool to support the feet, and positive reinforcement are important. Toilet anxiety is common in children who have experienced painful defaecation - a calm, non-pressured approach with praise (not punishment) is essential. Increase fluid intake and dietary fibre; a 2-4 week cow's milk elimination trial may be worth attempting in toddlers where macrogol response is poor and there are associated GI symptoms.

❍ Referral criteria

Refer to paediatric gastroenterology or general paediatrics for: any red flag features (see above); failure to respond to adequate macrogol therapy after 3 months; severe faecal incontinence requiring specialist behavioural support; suspected Hirschsprung's disease (rectal suction biopsy in secondary care); constipation associated with significant failure to thrive.