What are the characteristics and treatment options for functional constipation?

Characteristics of Functional Constipation

Functional constipation is diagnosed when a patient presents with at least two of the following symptoms for at least 12 weeks in the previous 12 months: straining during bowel movements, lumpy or hard stool, sensation of incomplete evacuation, sensation of anorectal blockage or obstruction, manual evacuation procedures to remove stool, or fewer than 3 bowel movements per week. 1, 2

Diagnostic Criteria and Symptoms

• Constipation is not merely infrequent bowel movements but encompasses a broader set of symptoms including hard stools, feeling of incomplete evacuation, abdominal discomfort, bloating, and distention 1
• Excessive straining, sense of anorectal blockage during defecation, and need for manual evacuation are key symptoms suggesting a defecatory disorder 1
• The Rome III criteria define chronic constipation as the presence of any two characteristic symptoms for at least 12 weeks in the previous 12 months (not necessarily consecutive) 1
• Reduced stool frequency is poorly correlated with delayed colonic transit, meaning patients with daily bowel movements may still experience constipation 1
• The Bristol Stool Form Scale is useful for objective symptom evaluation and differential diagnosis of secondary constipation 3

Clinical Subgroups

Defecatory Disorders

• Characterized primarily by impaired rectal evacuation from inadequate rectal propulsive forces and/or increased resistance to evacuation 1
• May result from high anal resting pressure ("anismus") and/or incomplete relaxation or paradoxical contraction of the pelvic floor and external anal sphincters ("dyssynergia") during defecation 1
• Structural disturbances (e.g., rectocele, intussusception) and reduced rectal sensation may coexist 1
• Also known as outlet obstruction, obstructed defecation, dyschezia, anismus, and pelvic floor dyssynergia 1
• Affects approximately 50% of patients with chronic constipation 4

Normal Transit Constipation (NTC)

• Characterized by normal anorectal function and normal colonic transit 1
• Patients may still experience symptoms of constipation despite normal transit time 1

Slow Transit Constipation (STC)

• Characterized by normal anorectal function but slow colonic transit 1
• Some patients have colonic motor disturbances (reduced colonic propulsive activity or increased uncoordinated motor activity in the distal colon) 1
• Resected colonic specimens from patients with STC who undergo colectomy reveal a marked reduction in colonic intrinsic nerves and interstitial cells of Cajal 1

Combination Disorders

• Some patients may have combination or overlap disorders (e.g., STC with defecatory disorders), possibly associated with features of irritable bowel syndrome 1

Pathophysiology

• Normal bowel function involves colonic absorption of fluids and transport of waste through peristalsis, with an average colonic transit time of 20-72 hours 1
• Constipation represents a disruption of these normal mechanisms 1
• Abnormal (reduced or increased) colonic sensation has been described in chronic constipation and may explain symptoms like abdominal pain and bloating 1
• Functional defecation disorders are mediated by failure of rectoanal coordination, paradoxical anal contraction, or insufficient relaxation of anal sphincter during defecation 4

Treatment Approaches

Non-Pharmacological Interventions

• Increasing fluid intake and dietary fiber can improve colonic transit in patients with constipation 5
• Physical activity should be encouraged as it benefits patients with constipation 5
• Biofeedback therapy is the mainstay treatment for dyssynergic defecation, aimed at improving coordination of abdominal and anorectal muscles 6
• Pelvic floor therapy should be offered to patients with evidence of an underlying defecatory disorder 1

Pharmacological Management

• Osmotic and stimulant laxatives should be offered to patients with chronic constipation 1
• Polyethylene glycol (PEG) is a recommended first-line treatment for constipation 5
• Stimulant laxatives such as bisacodyl or senna can be used to achieve one non-forced bowel movement every 1-2 days 5
• Prucalopride, a selective 5-HT4 serotonin receptor agonist, has shown efficacy in clinical trials for chronic idiopathic constipation, with significant improvements in complete spontaneous bowel movements compared to placebo 7
• Newer agents such as lubiprostone and linaclotide have shown benefit through meta-analysis 3

Clinical Pitfalls and Considerations

• Symptoms alone are inadequate to distinguish patients with defecation disorders from those with other types of constipation; detailed clinical evaluation and anorectal physiologic tests are required for definitive diagnosis 4
• After a failed empiric trial of laxatives, diagnostic testing is necessary to understand underlying anorectal and/or colonic pathophysiology 6
• No single test provides a comprehensive assessment for primary constipation; multiple tests provide complementary information 6
• Constipation can be secondary to diseases of the colon (stricture, cancer, anal fissure, proctitis), metabolic disturbances (hypercalcemia, hypothyroidism, diabetes mellitus), and neurologic disorders (parkinsonism, spinal cord lesions) 1
• Opioid-induced constipation is defined as constipation triggered or worsened by opioid analgesics and requires specific management approaches 1