Constipation

OVERVIEW

Constipation is a common clinical disorder characterized by infrequent bowel movements, hard/lumpy stools, excessive straining, a sensation of incomplete evacuation, or the need for manual maneuvers to facilitate defecation.

Diagnostic Threshold (Rome IV Criteria): Symptoms present for >= 3 months (with onset >= 6 months prior) including < 3 spontaneous bowel movements per week, along with straining, hard stools (Bristol Stool Form Scale Types 1–2), or incomplete evacuation in >= 25% of defecations.

Pathophysiologic Subtypes

• Primary (Functional): Normal-transit constipation (most common), Slow-transit constipation, or Pelvic Floor Dysfunction (Dyssynergic Defecation / Anismus).
• Secondary: Organic, metabolic, endocrine, neurogenic, structural, or medication-induced.

APPROACH

Step 1: Red Flag Screening (Rule Out Colorectal Malignancy & Organic Disease)

• Screen for “ALARM” Red Flags:
  • Age >= 50 years with new-onset or persistent constipation.
  • Loss of weight (unintentional/unexplained) or appetite.
  • Authentic hematochezia (rectal bleeding) or melena.
  • Recent change in bowel habit to constipation (especially if alternating with diarrhea).
  • Marked family history of Colorectal Cancer (CRC) or Inflammatory Bowel Disease (IBD).
  • Other Red Flags: Unexplained Iron Deficiency Anemia, severe refractory abdominal pain, palpable abdominal/rectal mass, fever, nocturnal symptoms.

Step 2: Perform Mandatory Digital Rectal Examination (DRE)

• Assess for fecal impaction, anal fissure, stricture, hemorrhoids, rectocele, rectal prolapse, or pelvic floor dyssynergia (failure of levator ani/anal sphincter relaxation during simulated evacuation).

Step 3: Diagnostic Branching Logic

• Red Flags Present / Age >= 50 with New Onset: -> Urgent Colonoscopy (Rule out obstructing colorectal carcinoma).
• Fecal Impaction Present on DRE: -> Immediate disimpaction protocol (High-dose Osmotic Laxatives + Suppositories / Enemas).
• No Red Flags: -> Empirical trial of conservative lifestyle modifications + Osmotic / Stimulant Laxatives for 4–8 weeks.
• Refractory to Medical Laxative Therapy: -> Refer for Anorectal Manometry & Balloon Expulsion Test (evaluates dyssynergic defecation) or Colon Transit Study.

DIFFERENTIAL DIAGNOSIS

Primary / Functional Constipation:

• Normal-Transit Constipation (NTC – Most Common):
  • Distinguishing features: Normal colonic transit time; hard stools, abdominal bloating/discomfort, good response to dietary fiber and standard laxatives.
• Slow-Transit Constipation (STC / Colonic Inertia):
  • Distinguishing features: Predominantly young women; markedly delayed colonic transit; infrequent urge to defecate (e.g., once every 1–2 weeks), severe bloating, poor response to fiber.
• Pelvic Floor Dysfunction (Dyssynergic Defecation / Anismus):
  • Distinguishing features: Paradoxical contraction or failure of relaxation of the puborectalis muscle and external anal sphincter during defecation; prolonged straining, feeling of anal blockage, requirement for manual/digital evacuation maneuvers.

Secondary Causes (Reversible & Organic):

• Medication-Induced (Most Common Secondary Cause):
  • Offending Agents: Opioids (Codeine, Morphine, Oxycodone), Anticholinergics, Calcium Channel Blockers (Verapamil), Iron supplements, Aluminium antacids, TCAs, 5-HT3 antagonists (Ondansetron).
• Endocrine / Metabolic:
  • Distinguishing features:
    • Hypothyroidism (weight gain, fatigue, cold intolerance, dry skin)
    • Hypercalcaemia (polyuria, confusion, “groans”), Diabetes Mellitus (autonomic neuropathy), Uremia.
• Structural / Mechanical Obstruction:
  • Distinguishing features: Colorectal Carcinoma, Diverticular Stricture, Volvulus, Rectocele, Enterocele, Anal Fissure (severe tearing pain during defecation causing voluntary stool retention).
• Neurological / Systemic:
  • Distinguishing features: Parkinson’s Disease (early autonomic sign), Spinal Cord Injury, Multiple Sclerosis, Systemic Sclerosis.

INVESTIGATIONS

First-Line / Bedside & Initial Laboratory Workup:

• Digital Rectal Examination (DRE): Evaluates resting sphincter tone, paradoxical contraction during push, rectal masses, and stool consistency/impaction.
• Basic Blood Panel (To exclude secondary metabolic/endocrine causes):
  • Serum Corrected Calcium: Rule out hypercalcaemia.
  • Thyroid Function Tests (TSH, Free T4): Rule out hypothyroidism.
  • Full Blood Count (FBC): Screen for microcytic anemia (occult GI blood loss).
  • Electrolytes & Creatinine: Rule out hypokalemia or renal impairment.

Targeted / Diagnostic Imaging & Functional Strategy:

• Colonoscopy: Mandatory in patients with red flags, new-onset constipation >= 50 years, or suspicion of structural/neoplastic obstruction.
• Anorectal Manometry & Balloon Expulsion Test: Gold standard diagnostic combination for Pelvic Floor Dysfunction / Dyssynergic Defecation. (Inability to expel a 50 mL water-filled balloon within 1–2 minutes confirms evacuation disorder).
• Radiopaque Marker Colon Transit Study (Sitz Marks Study): Evaluates for Slow-Transit Constipation. (Abdominal X-ray taken on Day 5 after ingesting capsule containing radiopaque markers; retention of > 20% markers indicates delayed colonic transit).
• Dynamic Defecography (MRI or Fluoroscopic): Evaluates structural outlet obstruction (Rectocele, Intussusception, Enterocele).

CRITICAL MANAGEMENT

Acute Fecal Impaction Management:

• First-Line Oral / Rectal Regimen: High-dose Polyethylene Glycol (Macrogol) (e.g., 8 sachets in 1 L water over 6 hours) OR Glycerol / Phosphate Enemas +/- manual softening if impaction is in the distal rectum.

First-Line Pharmacological Stepped Approach for Chronic Constipation:

• Step 1: Dietary & Lifestyle Modifications:
  • Increase dietary fiber intake progressively to 25–30 g/day + fluid intake (1.5–2.0 L/day) + regular exercise.
• Step 2: Bulk-Forming Laxatives:
  • Psyllium / Ispaghula Husk or Sterculia. (Must drink adequate water; avoid in fecal impaction or opioid constipation).
• Step 3: Osmotic Laxatives (First-Line Medical Therapy):
  • Polyethylene Glycol (Macrogol) OR Lactulose OR Magnesium Hydroxide. Keeps water within the bowel lumen.
• Step 4: Stimulant Laxatives (Add-on / Rescue):
  • Senna, Bisacodyl, or Sodium Picosulfate. Stimulates enteric nerves to increase peristalsis.
• Step 5: Targeted Prescription Agents for Refractory Cases:
  • Prucalopride: Selective 5-HT4 receptor agonist (stimulates colonic mass movements).
  • Lubiprostone / Linaclotide: Secretagogues (increase intestinal chloride and water secretion).
  • Peripherally Acting Mu-Opioid Receptor Antagonists (PAMORAs): Naldemedine or Naloxegol specifically for Opioid-Induced Constipation (OIC).

Dyssynergic Defecation Specialised Treatment:

• Anorectal Biofeedback Therapy: First-line gold standard treatment (retrains pelvic floor muscle relaxation during defecation; high long-term success rate > 70–80%).