Pediatric Constipation: MCCQE1 Preparation Guide

Introduction

Constipation in children is defined by a delay or difficulty in defecation, present for two or more weeks, sufficient to cause significant distress to the patient. It is a prevalent issue in Canada, affecting approximately 15-30% of children.

For MCCQE1 preparation, it is crucial to understand that the vast majority of these cases are functional, often triggered by painful bowel movements leading to withholding behavior.

Etiology and Pathophysiology

Understanding the timing of onset is critical for the Canadian medical licensing exam. There are three main periods where constipation typically arises:

1. Introduction of solid foods (6 months to 1 year)
2. Toilet training (2 to 3 years)
3. Start of school (School-age entry)

Functional vs. Organic Causes

Clinical Presentation and History

A thorough history is the most powerful tool for the MCCQE1. You must identify red flags.

The “Rome IV” Diagnostic Criteria

Must include 2 or more of the following occurring at least once per week for a minimum of 1 month (for infants/toddlers) or 1 month (for children/adolescents):

1. Two or fewer defecations in the toilet per week.
2. At least one episode of fecal incontinence per week.
3. History of retentive posturing or excessive volitional stool retention.
4. History of painful or hard bowel movements.
5. Presence of a large fecal mass in the rectum.
6. History of large diameter stools that may obstruct the toilet.

Red Flags (Alarm Signs) for Organic Disease

Physical Examination

For the MCCQE1, focus on ruling out organic causes through a targeted exam.

1. Growth Parameters: Plot height and weight. Poor growth suggests organic disease (Hypothyroidism, Celiac).
2. Abdomen: Palpate for fecal masses (typically left lower quadrant).
3. Lumbosacral Spine: Inspect for sacral dimples, hair tufts, or gluteal cleft deviation (Spinal dysraphism).
4. Neurologic: Lower extremity tone, strength, and reflexes (Deep Tendon Reflexes).
5. Perianal/Rectal Exam:
   • Visual: Check for fissures (functional), skin tags (Crohn’s), anterior anus.
   • Digital Rectal Exam (DRE):
     • Functional: Large amount of stool in the vault, normal tone.
     • Hirschsprung: Snug sphincter, empty vault, “blast sign” (explosive stool/gas upon withdrawal).

Investigations

• Routine: No labs needed for clear functional constipation.
• If Red Flags Present:
  • TSH, Calcium: Rule out hypothyroidism/hypercalcemia.
  • Celiac Screen (TTG-IgA): If failure to thrive or abdominal pain is prominent.
  • Sweat Chloride: If respiratory symptoms or failure to thrive (Cystic Fibrosis).
  • Lumbosacral MRI: If spinal abnormalities found.
  • Rectal Suction Biopsy: Gold standard for Hirschsprung disease (absence of ganglion cells).

Management

The Canadian Paediatric Society (CPS) guidelines emphasize a multi-faceted approach. Management is often long-term (months to years).

Canadian Guidelines (CPS)

The Canadian Paediatric Society emphasizes:

1. Early intervention: Treat aggressively to prevent chronic megarectum.
2. Medication adherence: Parents often stop meds too early. Treatment should continue for months after symptoms resolve.
3. School support: Letters may be needed to allow children private access to bathrooms at school.

Key Points to Remember for MCCQE1

• Most common cause: Functional (retentive) constipation.
• Hirschsprung Disease: Suspect in any neonate who fails to pass meconium in the first 48 hours. Diagnosis: Rectal suction biopsy.
• Encopresis: In functional constipation, this is overflow incontinence (liquid stool leaking around hard mass). Do not confuse with diarrhea.
• Treatment: PEG 3350 is the gold standard in Canada.
• Imaging: Abdominal X-rays are generally not indicated for diagnosis.

Sample Question

Scenario: A 4-year-old girl is brought to your office by her parents due to “diarrhea” and soilng her underwear daily for the past 3 months. She was toilet trained at age 3 but has recently regressed. The parents report she often hides behind the sofa and crosses her legs when she needs to go. On physical examination, her abdomen is soft but a palpable mass is noted in the left lower quadrant. Her height and weight are at the 50th percentile. An anal exam shows some fecal soiling but normal placement.

Which of the following is the most appropriate initial management step?

• A. Reassure the parents that this is behavioral and will resolve with time
• B. Order an abdominal X-ray to confirm fecal loading
• C. Prescribe a high-fiber diet and increased water intake exclusively
• D. Initiate disimpaction with oral Polyethylene Glycol (PEG 3350)
• E. Refer immediately for a rectal suction biopsy

Explanation

The correct answer is:

• D. Initiate disimpaction with oral Polyethylene Glycol (PEG 3350)

Detailed Analysis:

• D is correct: The clinical presentation is classic for functional constipation with encopresis (overflow incontinence). The “diarrhea” is actually liquid stool leaking around a fecal impaction. The “hiding and leg crossing” is retentive posturing. The palpable mass confirms fecal loading. Canadian guidelines recommend disimpaction (clean out) as the first step in medical management, preferably using oral PEG 3350.
• A is incorrect: While behavioral, it is a physiological problem (megarectum) that requires medical treatment. Ignoring it will worsen the condition.
• B is incorrect: Clinical diagnosis is sufficient based on the history (retentive behavior, soiling) and physical exam (mass). X-rays are discouraged (Choosing Wisely).
• C is incorrect: While fiber and fluids are important for prevention, they are ineffective for disimpaction of a large fecal mass and may cause increased abdominal pain without clearing the blockage.
• E is incorrect: Rectal biopsy is indicated for suspected Hirschsprung disease. This child has no red flags (no delayed meconium, normal growth, onset at age 4, retentive behavior), making Hirschsprung’s highly unlikely.

References

1. Canadian Paediatric Society. (2011, reaffirmed 2019). Managing functional constipation in children. Position Statement.
2. Rowan-Legg, A. (2011). Managing functional constipation in children. Paediatrics & Child Health, 16(10), 661-665.
3. Choosing Wisely Canada. (2020). Paediatrics: Five Things Physicians and Patients Should Question.
4. Medical Council of Canada. (2023). MCCQE Part I Clinical Decision-Making and Multiple-Choice Question Guidelines.
5. Tabbers, M. M., et al. (2014). Evaluation and treatment of functional constipation in infants and children: evidence-based recommendations from ESPGHAN and NASPGHAN. Journal of Pediatric Gastroenterology and Nutrition, 58(2), 258-274.