How do you differentiate between all types of constipation?

Differentiating Between Types of Constipation

After initial history and physical examination, constipation can be classified into five distinct categories: (1) normal transit constipation (NTC), (2) slow transit constipation (STC), (3) defecatory disorders, (4) combination disorders (STC with defecatory disorder), or (5) secondary constipation due to medications, metabolic disorders, or structural lesions. 1

Initial Clinical Assessment

Key Historical Features to Elicit

The questioning must be specific to identify the predominant symptom pattern: 1

• Infrequency alone suggests NTC or STC 1
• Prolonged excessive straining with soft stools or inability to pass enema fluid strongly indicates defecatory disorders 1
• Need for perineal/vaginal pressure or digital evacuation is an even stronger clue for defecatory disorders 1
• Abdominal pain, bloating, and malaise unrelated to defecation suggests underlying irritable bowel syndrome 1

Critical Physical Examination Components

A careful digital rectal examination with specific maneuvers is essential and should be performed before referral for anorectal manometry: 1

• Observe perineal descent during simulated evacuation and elevation during squeeze in left lateral position 1
• Check for patulous anal opening during simulated defecation, which suggests neurogenic constipation 1
• Assess puborectalis muscle contraction during squeeze 1
• Evaluate for acute localized tenderness along puborectalis, indicating levator ani syndrome 1
• Instruct patient to "expel my finger" to assess integrated expulsionary forces 1

However, a normal digital rectal examination does not exclude defecatory disorders. 1

Diagnostic Testing Algorithm

Initial Laboratory Screening

In the absence of alarm symptoms, only a complete blood cell count is necessary. 1

Metabolic tests (glucose, calcium, thyroid-stimulating hormone) are NOT recommended for chronic constipation unless other clinical features warrant them. 1

When to Perform Structural Evaluation

Colonoscopy should NOT be performed unless: 1

• Alarm features present: blood in stools, anemia, unintentional weight loss 1
• Abrupt onset of constipation 1
• Age >50 years without previous colorectal cancer screening 1

Specialized Testing Sequence

The testing sequence depends on initial findings: 1

1. Anorectal testing first (manometry, balloon expulsion test) to identify defecatory disorders 1
2. Colonic transit study should be evaluated if:
   • Anorectal tests do not show defecatory disorder, OR
   • Symptoms persist despite treatment of defecatory disorder 1

Classification of Constipation Types

1. Normal Transit Constipation (NTC)

• Normal anorectal function with normal colonic transit 1, 2
• Often associated with irritable bowel syndrome features when pain is prominent 1

2. Slow Transit Constipation (STC)

Characterized by: 1, 2

• Normal anorectal function with slow colonic transit 1, 2
• Reduced colonic propulsive activity or increased uncoordinated distal colonic motor activity 1, 2
• Marked reduction in colonic intrinsic nerves and interstitial cells of Cajal on resected specimens 1, 2
• Infrequent bowel movements and abdominal bloating 3

3. Defecatory Disorders

Primary features: 1, 2

• Impaired rectal evacuation from inadequate rectal propulsive forces and/or increased resistance to evacuation 1, 2
• High anal resting pressure ("anismus") and/or incomplete relaxation or paradoxical contraction of pelvic floor and external anal sphincters ("dyssynergia") 1, 2
• Difficulty passing soft stools or enema fluid indicates pronounced evacuatory defects 1
• May have slow colonic transit that improves once defecatory disorder is treated 1

Other terms include: outlet obstruction, obstructed defecation, dyschezia, anismus, pelvic floor dyssynergia 1

4. Combination Disorders

Some patients have overlap: 1

• STC with defecatory disorders 1
• May also have features of irritable bowel syndrome 1

5. Secondary Constipation

Must exclude these causes: 1, 2

Medication-Induced

• Opioids (most common, no tolerance develops) 2
• Anticholinergics, calcium channel blockers 1, 2

Metabolic Disorders

• Hypothyroidism, hypercalcemia, hypokalemia, diabetes mellitus, uremia 2

Neurologic Disorders

• Parkinsonism, spinal cord lesions 2

Structural Lesions

• Colon stricture, cancer, anal fissure, proctitis 2
• Radiation-induced strictures or dysmotility 2
• Abdominal or pelvic masses 2

Common Pitfalls to Avoid

Failure to recognize defecatory disorders is a frequent reason for therapeutic failure because these do not respond to standard laxative programs. 1

Do not assume normal digital rectal examination excludes defecatory disorders - specialized anorectal testing is still needed if clinical suspicion is high. 1

Discontinue constipating medications before further testing when feasible. 1

Remember that after complete bowel purge, it takes several days for residue to accumulate - this is not treatment failure. 1