Management of constipation: A narrative review of evolving strategies and methodological challenges

Table 1 Classification and etiologies of constipation

Category	Subtype	Causes	Key features
Primary (functional) constipation	Normal-transit constipation	Associated with irritable bowel syndrome-constipation predominant, stress, and visceral hypersensitivity. Low fiber and fluid intake. Sedentary lifestyle	Normal colonic transit time, but patient feels constipated due to perceived difficulty. Reduced bulk of stool. Weaker colonic stimulation. Dry stools
	Slow-transit constipation	Colonic neuropathy. Colonic myopathy. Possible association with eating disorders. Altered serotonin levels	Delayed colonic transit time due to impaired colonic motility. Predominant in young women. Reduced high-amplitude propagated contractions
	Defecatory disorders (pelvic floor dysfunction/outlet obstruction)	Dyssynergic defecation (inappropriate pelvic floor contraction). Impaired rectal propulsive forces. Obstructed defecation syndrome. Structural abnormalities (rectocele, rectal prolapse, excessive perineal descent)	Failure of anorectal coordination. Difficult or blocked evacuation
Secondary (organic) constipation	Systemic/metabolic/endocrine	Diabetes mellitus. Dehydration. Amyloidosis. Uremia. Chronic kidney disease. Pregnancy. Hypercalcemia. Hypokalemia. Hypothyroidism	Systemic or metabolic slowing of the GI tract
	Neurologic	Parkinson’s disease. Multiple sclerosis. Spinal cord injury. Stroke. Hirschsprung disease. Autonomic neuropathies	Due to impaired neural control of bowel movements and defecation
	Structural/mechanical	Colonic strictures (ischemia, radiation induced, inflammatory). Colorectal cancer. Anal fissures (pain leading to stool retention). Megacolon	Mechanical obstruction or pain-related stool withholding
	Medication-induced	Opioids. Anticholinergics (TCAs, antihistamines). Calcium channel blockers. Iron supplements. Calcium or aluminum containing antacids. Antipsychotics/anticonvulsants (gabapentin, pregabalin). Diuretics (due to dehydration)	Common and most important cause. Due to motility or increased water absorption of water or reduced secretions

GI: Gastrointestinal; TCA: Tricyclic antidepressant.