What is functional constipation?

Functional Constipation Definition

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

Core Diagnostic Framework

The Rome IV criteria establish functional constipation as a symptom-based diagnosis requiring:

• Minimum duration: At least 12 weeks (not necessarily consecutive) within the previous 12 months 1, 2
• Symptom threshold: At least 2 of 6 characteristic symptoms must be present 1, 3

The Six Defining Symptoms

1. Straining during bowel movements 1
2. Lumpy or hard stool consistency 1
3. Sensation of incomplete evacuation 1
4. Sensation of anorectal blockage or obstruction 1
5. Manual maneuvers required to facilitate defecation (digital evacuation or perineal/vaginal support) 1
6. Fewer than 3 bowel movements per week 1

Critical Conceptual Understanding

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 This is a crucial clinical pitfall—patients with daily bowel movements can still have functional constipation if they meet other diagnostic criteria, as reduced stool frequency correlates poorly with delayed colonic transit. 1, 3

What Functional Constipation Is NOT

• Not opioid-induced constipation: This is a distinct entity defined by Rome IV criteria as "constipation triggered or worsened by opioid analgesics" requiring specific management approaches different from functional constipation 2
• Not secondary constipation: Must exclude diseases of the colon (stricture, cancer, anal fissure, proctitis), metabolic disturbances (hypercalcemia, hypothyroidism, diabetes mellitus), and neurologic disorders (Parkinsonism, spinal cord lesions) 1, 2
• Not medication-induced: Must exclude constipation from anticholinergics, calcium channel blockers, and other constipating medications 2

Clinical Subgroups of Functional Constipation

Once diagnosed, functional constipation can be further classified into three pathophysiologic subtypes:

Normal Transit Constipation (NTC)

• Normal anorectal function with normal colonic transit 1
• Patients experience constipation symptoms despite normal transit time 1
• Often associated with irritable bowel syndrome features 2

Slow Transit Constipation (STC)

• Normal anorectal function but slow colonic transit 1
• Colonic motor disturbances with reduced propulsive activity 2
• Average normal colonic transit time is 20-72 hours; STC exceeds this 1

Defecatory Disorders

• Impaired rectal evacuation from inadequate rectal propulsive forces and/or increased resistance to evacuation 1
• Key symptoms: excessive straining, sense of anorectal blockage during defecation, need for manual evacuation 1
• Critical pitfall: Prolonged excessive straining with soft stools or inability to pass enema fluid strongly indicates defecatory disorders, not simple constipation 2

Combination Disorders

• STC with defecatory disorders may be associated with features of irritable bowel syndrome 1

Distinguishing from Irritable Bowel Syndrome with Constipation (IBS-C)

The fundamental difference between functional constipation and IBS-C is the presence or absence of abdominal pain:

• IBS-C: Constipation with recurring abdominal pain, bloating, and abdominal distension 4, 5
• Functional constipation: Constipation symptoms without the pain component being predominant 4, 5
• However, this distinction is not "all or nothing"—there is overlap in the spectrum 4

Pathophysiologic Mechanisms

Normal bowel function involves colonic absorption of fluids and transport of waste through peristalsis; functional constipation represents a disruption of these normal mechanisms. 1 Abnormal colonic sensation has been described in chronic constipation and may explain symptoms like abdominal pain and bloating. 1

Common Clinical Pitfalls

• Do not assume daily bowel movements exclude constipation: The presence of daily bowel movements does not exclude constipation or defecatory disorders 3
• Recognize overflow incontinence: Fecal soiling with constipation represents overflow of liquid stool around retained hard fecal matter, indicating incomplete evacuation and suggesting a defecatory disorder with fecal impaction 3
• Symptom pattern matters for subtyping: Infrequency alone suggests NTC or STC, while prolonged excessive straining with soft stools or need for digital evacuation strongly indicates defecatory disorders 2