Constipation refers to fewer than three bowel movements per week, with dry, hard stools and difficulty in defecation. Difficulty in defecation includes straining, prolonged defecation time, sensations of anal obstruction, incomplete evacuation, or the need for manual assistance during defecation. Chronic constipation is defined as constipation lasting for more than 12 weeks.
Etiology and Pathogenesis
The causes of constipation can be classified into functional constipation and organic constipation. The pathophysiological mechanisms of functional constipation remain incompletely understood and may involve colonic transit abnormalities, defecatory dysfunction, and intestinal microbiota imbalance. Functional constipation can be further categorized into slow transit constipation (STC), normal transit constipation (NTC), defecatory disorder (dyssynergic defecation), and mixed-type constipation. Common causes of constipation include:
Anorectal, Colorectal, and Pelvic Floor Disorders
These include rectal prolapse, inflammatory bowel disease, intestinal tuberculosis, post-traumatic or post-surgical intestinal strictures, colorectal tumors and metastasis-related intestinal strictures, rectal intussusception, rectocele, pelvic floor dyssynergia, perineal descent, and congenital megacolon.
Systemic Diseases
Hypothyroidism, diabetes, hypercalcemia, rheumatic autoimmune diseases, amyloidosis, dermatomyositis, and scleroderma are among the systemic conditions that may cause constipation.
Neurological Disorders
Parkinson's disease, multiple sclerosis, impaired consciousness, spinal cord injury, cerebral infarction, and brain atrophy are common neurological causes of constipation.
Dietary and Medication Factors
Insufficient food intake, inadequate hydration, consumption of highly refined foods, low intake of vegetables and fruits, prolonged sitting or bed rest, and lack of physical activity can reduce intestinal stimulation or weaken intestinal motility, leading to constipation. Chronic use of opioids, psychotropic drugs, calcium channel blockers, and anticholinergic medications may also result in secondary constipation.
Psychological and Emotional Factors
Psychological stress, anxiety, depression, sleep disorders, traumatic experiences during childhood, chronic stress in daily life, negative life events, and changes in daily routines, such as travel, can disrupt autonomic nervous system function, alter bowel habits, and contribute to constipation.
Clinical Manifestations
Constipation is characterized by fewer than three bowel movements per week, difficulty in defecation, prolonged defecation time, and the passage of small amounts of dry, hard stools. Symptoms may include sensations of anal obstruction, incomplete evacuation, or rectal heaviness, often accompanied by lower abdominal distension, loss of appetite, fatigue, dizziness, irritability, anxiety, and insomnia. Some patients may experience anal pain, anal fissures, or hemorrhoidal bleeding due to straining during the passage of hard stools.
Diagnosis and Differential Diagnosis
The diagnosis of constipation is based on clinical symptoms. A detailed medical history, thorough physical examination, and appropriate laboratory and imaging studies are critical for diagnosing and differentiating constipation. Patients presenting with alarm symptoms such as hematochezia, melena, positive fecal occult blood tests, fever, anemia, weight loss, or abdominal masses should undergo comprehensive evaluation to exclude organic causes of constipation.
Endoscopy
Colonoscopy allows direct visualization of the colonic and rectal mucosa to identify potential lesions and rule out organic diseases of the colon and rectum. Patients with alarm symptoms such as rectal bleeding, anemia, weight loss, or abdominal masses should undergo colonoscopy promptly.
Gastrointestinal X-ray
Barium meal studies can provide insights into gastrointestinal motility. Under normal conditions, barium reaches the splenic flexure within 12–18 hours and is fully expelled from the colon within 24–72 hours. In constipation, delayed emptying may be observed. Barium enema studies can detect colonic dilation, redundant sigmoid colon, and intestinal strictures, aiding in the diagnosis of the underlying cause of constipation.
Colonic Transit Study
Using radiopaque markers, abdominal X-rays are taken at scheduled intervals after ingestion to track marker movement through the colon. This test evaluates the speed and location of colonic contents and identifies sites of obstruction, helping to differentiate slow transit constipation from outlet obstruction constipation. Alternatively, radionuclide scanning can measure colonic transit time with reduced radiation exposure, although it requires specialized and costly equipment.
Defecography
Barium enema defecography simulates the defecation process, allowing dynamic assessment of the anus, rectum, and pelvic floor muscles during defecation. This test is useful for diagnosing outlet obstruction constipation caused by conditions such as rectocele and pelvic floor dyssynergia.
Anorectal Manometry
Anorectal manometry involves the insertion of a pressure-sensing device into the rectum to assess the function and coordination of the internal and external anal sphincters, pelvic floor muscles, and rectum during contraction and relaxation. This test aids in the diagnosis of outlet obstruction constipation.
Electromyography (EMG) of Anal Muscles
Anal EMG is a routine diagnostic technique for evaluating pelvic floor muscle abnormalities. Electrophysiological methods are used to assess the function of the puborectalis muscle and external anal sphincter, supporting the diagnosis of myogenic constipation. This test is also useful for diagnosing pelvic floor spasm syndrome, puborectalis syndrome, rectal prolapse, and perineal descent syndrome.
Treatment
The treatment of constipation should be tailored to its specific type, with the goals of alleviating symptoms, restoring normal bowel motility, and improving physiological defecation function.
Organic Constipation
Treatment should focus on addressing the underlying cause. Laxatives may be used temporarily to relieve symptoms of constipation.
Functional Constipation
Symptomatic treatment should be individualized, aiming to alleviate patient concerns, reduce the frequency of constipation episodes, decrease symptom severity, and improve quality of life.
Dietary Therapy and Psychological Intervention
Increasing dietary fiber intake, drinking adequate water, establishing regular bowel habits, engaging in physical activity, and avoiding the misuse of laxatives are essential measures. Dietary fiber is not absorbed by the body and has hydrophilic properties, which allow it to absorb water in the intestinal lumen, increase stool volume, stimulate colonic motility, and enhance defecation ability, thereby alleviating constipation symptoms. Foods rich in dietary fiber include wheat bran, vegetables, and fruits. After ruling out organic causes of constipation, psychological interventions may be offered to reduce patient concerns, build confidence in treatment, and improve compliance with therapy.
Pharmacological Treatment
Medications such as laxatives, prokinetic agents, secretagogues, electrolyte solutions, and lubricants may be selected based on individual needs.
Laxatives
Laxatives work by stimulating intestinal secretion, reducing absorption, increasing intraluminal osmotic pressure, and promoting bowel movement. They are generally classified into the following types:
- Stimulant laxatives (e.g., rhubarb, senna, phenolphthalein, castor oil)
- Saline laxatives (e.g., magnesium sulfate)
- Osmotic laxatives (e.g., mannitol, lactulose)
- Bulk-forming laxatives (e.g., bran, methylcellulose, polyethylene glycol, agar)
- Lubricant laxatives (e.g., liquid paraffin, glycerin)
Stimulant laxatives act quickly and effectively but may cause drug dependence and melanosis coli with long-term use. Osmotic laxatives have fewer side effects and can be used for extended periods. In cases of acute constipation, saline, stimulant, or lubricant laxatives may be used, but their use should not exceed one week. For chronic constipation, bulk-forming laxatives are preferred, and stimulant laxatives should not be used long-term. For fecal impaction, manual assistance or enemas with saline or other solutions may be required.
Prokinetic and Secretagogue Medications
Commonly used prokinetic agents include highly selective 5-HT4 receptor agonists such as mosapride and prucalopride, which stimulate enteric neurons, promote gastrointestinal smooth muscle motility, enhance small and large intestinal transit, and improve constipation symptoms. Secretagogue medications include lubiprostone and linaclotide. Lubiprostone selectively activates chloride channels, promoting the movement of chloride ions, sodium ions, and water into the intestinal lumen. Linaclotide acts on guanylate cyclase-C receptors in intestinal epithelial cells to enhance chloride ion secretion. Both medications effectively alleviate constipation symptoms, with linaclotide additionally increasing the colonic pain threshold and relieving abdominal discomfort and pain.
Probiotics
Probiotics may prevent the colonization and invasion of harmful bacteria and restore the balance of intestinal microbiota. Supplementation with probiotics can regulate normal intestinal motility and may help alleviate constipation and abdominal distension. Commonly used probiotics include bifidobacterium triple viable capsules, lactobacillus tablets, and clostridium butyricum tablets.
Biofeedback Therapy
Biofeedback therapy involves the use of rectal manometry and electromyography devices to help patients visualize the functional state of their pelvic floor muscles during defecation. Through guided learning, patients can correct and rebuild the rectoanal reflex, improve muscle coordination during defecation, and increase defecation frequency. This method is effective for some cases of pelvic floor dysfunction-related constipation.
Surgical Treatment
For patients with refractory constipation unresponsive to long-term medical therapy, surgical treatment may be considered after careful deliberation and shared decision-making between the physician and the patient.