What are the differential diagnoses and initial management approaches for constipation?

Differential Diagnoses for Constipation

Constipation can be classified as primary (functional) or secondary, with secondary causes including medications, metabolic disorders, neurologic conditions, and anatomic abnormalities that must be systematically excluded through targeted history and examination. 1, 2

Primary (Functional) Constipation

• Normal transit constipation: Most common form where stool moves through colon at normal speed but patients perceive difficulty with evacuation 2
• Slow transit constipation: Delayed colonic transit time requiring specialized testing (colonic transit studies, manometry) to diagnose 1, 3
• Defecatory disorders (dyssynergic defecation): Inability to coordinate pelvic floor muscles during evacuation, characterized by excessive straining with soft stools and inability to pass enema fluid 4, 2

Secondary Causes - Medications

• Opioid-induced constipation: Most common drug-related cause; all patients on opioids should receive prophylactic laxatives unless contraindicated by pre-existing diarrhea 5
• Other constipating medications: Anticholinergics, calcium channel blockers, antidepressants, iron supplements - complete medication review is essential 5, 1

Secondary Causes - Metabolic/Endocrine

• Hypothyroidism: Check thyroid function if clinically suspected 5, 6
• Hypercalcemia: Check corrected calcium levels when suspected clinically 5, 6
• Diabetes mellitus: Can cause autonomic neuropathy affecting bowel motility 7

Secondary Causes - Neurologic

• Spinal cord compression syndrome: Requires full neurological examination including assessment of anal sphincter tone (lax with colonic hypotonia) and rectal sensation 5
• Parkinson's disease, multiple sclerosis: Degenerative processes affecting enteric nervous system 5

Secondary Causes - Anatomic/Structural

• Colorectal cancer: Suspect with rectal bleeding, unexplained weight loss, or palpable mass on digital rectal examination 4
• Strictures: From surgery, radiation, inflammatory bowel disease, or adhesions 5
• Hirschsprung's disease: In children, rectum is typically empty and tight on examination (versus distended and full in functional constipation) 8
• Rectal prolapse: Full-thickness protrusion showing concentric protrusion of rectal wall on examination 4

Complications Presenting as Constipation

• Fecal impaction: Large mass of dry, hard stool confirmed by digital rectal examination; may present with overflow diarrhea 5, 4
• Bowel obstruction: Complete obstruction is surgical emergency with absolute constipation, distended abdomen, and regular vomiting 5

Inflammatory/Infectious

• Proctitis: From inflammatory bowel disease, radiation, or sexually transmitted infections; requires sigmoidoscopy with biopsy 4
• Severe colitis: Contraindication for certain treatments like enemas 5

Functional Disorders with Constipation Features

• Irritable bowel syndrome with constipation: Pre-existing diagnosis should be noted in history 5, 9
• Levator ani syndrome: Acute localized tenderness along puborectalis muscle on digital rectal examination 4

Age-Related Considerations

• Elderly patients: Five times more prone to constipation due to degenerative changes in enteric nervous system; prevalence 24-50% in community-dwelling elderly and 74% in nursing home residents 5, 6
• Neonatal/congenital: Constipation present from birth most likely congenital in origin (e.g., Hirschsprung's disease) 8

Initial Management Approach

Begin with targeted history focusing on: date of last bowel movement, stool frequency and consistency, presence of urge to defecate, sensation of complete evacuation, blood or mucus, current laxative use, need for digital manipulation, medication list, dietary fiber and fluid intake, physical activity level, and comorbid conditions. 5, 6

Physical examination must include: abdominal examination (distension, masses, tenderness, bowel sounds), perineal inspection (fissures, prolapse, hemorrhoids), and digital rectal examination (sphincter tone, impacted feces, masses, hemorrhoids). 5, 6

Investigations are not routinely necessary but should include corrected calcium and thyroid function if clinically suspected; more extensive workup warranted for severe symptoms, sudden changes in bowel habits, blood in stool, or elderly patients relative to disease stage. 5, 6

Plain abdominal X-ray may be useful to image extent of fecal loading and exclude bowel obstruction, though limited as standalone tool. 5