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Constipation most classically refers to reduced defecation frequency and hard stools. Physicians typically define constipation as fewer than three bowel movements per week. Patients more frequently describe constipation as defecatory difficulty with predominant complaints of straining or hard stools. This holds particularly true in older adults. Understanding the patient’s view of constipation assists in evaluation and treatment.

The normal defecatory process requires sufficient cognition (recognizing the need to defecate), normal colon transit, and normal function of the pelvic floor muscles and anal sphincters. Normal colon transit ranges from 24 to 72 hours. Defecation is most often preceded by high‐amplitude propagated colonic contractions. These colonic contractions occur in response to meals, particularly those with higher concentrations of calories and fat. Colonic motility is also more robust during waking hours and quiescent during sleep. Colonic activity propels stool into the rectum, causing distension and reflex relaxation of the internal anal sphincter; this prompts reflex contraction of the external anal sphincter and pelvic floor muscles. The brain registers the urge to defecate, and at an appropriate time, this may be voluntarily initiated through a set of coordinated actions. Initiation of the defecation process starts with relaxation of the puborectalis muscle, opening of the anorectal angle, and relaxation of the external anal sphincter. This is accompanied by a simultaneous rise in intra‐abdominal pressure assisted by valsalva contraction of the abdominal wall muscles (Figure 20.1). An abnormality affecting any of these areas results in the development of an altered bowel pattern (Table 20.1).

Constipation may be defined in many different ways. Simply stated, primary constipation refers to constipation without an obvious cause, and secondary constipation results from external aetiologies. These external causes of altered bowel function may include neuromuscular disorders, metabolic abnormalities, medications, insufficient diet, or mechanical factors obstructing the movement of stool. Constipation may be further defined as acute or chronic. Chronic constipation indicates that symptoms have been present for more than three months and typically dates back years. Acute constipation requires a more rapid investigation into the aetiology, including evaluation for structural abnormalities or recent medication changes. Patients with chronic constipation may initially be treated symptomatically with fibre and/or simple laxatives. Those not responding to usual treatments require further investigation to evaluate for evidence of slow‐transit constipation or dyssynergic defecation (also called pelvic outlet dysfunction). Although constipation commonly occurs in the setting of irritable bowel syndrome (IBS), new‐onset IBS occurs less frequently in older patients than younger ones. Specific criteria have been defined to aid practitioners in diagnosing constipation related to IBS. The Rome IV criteria are commonly used, with the most recent iteration in 2016.¹

The Bristol stool chart can be used to objectively describe bowel habits and classify patients into the correct subtype to ensure correct diagnosis and treatment. The Bristol stool form scale (BSFS) was developed in the 1990s in the Bristol Royal Infirmary, England.² The authors described seven types of stool:

 Type 1: Separate hard lumps, like nuts (hard to pass)

 Type 2: Sausage‐shaped, but lumpy

 Type 3: Like a sausage but with cracks on its surface

 Type 4: Like a sausage or snake, smooth and soft

 Type 5: Soft blobs with clearcut edges (passed easily)

 Type 6: Fluffy pieces with ragged edges, a mushy stool

 Type 7: Watery, no solid pieces, entirely liquid

Figure 20.1 Illustration of the defecatory process.

Table 20.1 Anatomical distribution of changes associated with constipation.

Central nervous system
Awareness of need to defecate
Cerebrovascular accident
Dementia Parkinson’s disease
Peripheral nervous system
Controls myogenic activity of puborectalis
Pudendal nerve injury
Enteric nervous system
Controls rectal sensory function, peristalsis, and internal anal sphincter
Parkinson’s disease
Desensitization (chronically distended rectum)
Diabetes mellitus
Skeletal muscle
Contraction/relaxation of puborectalis and external sphincter
Direct muscular damage (e.g. prior birth trauma, sphincterotomy)
Rheumatological disorders (e.g. scleroderma, reduced muscular strength)
Incoordination
Idiopathic

The authors classified stool types 1 and 2 as being associated with constipation. The BSFS is a convenient way for patients to describe their bowel habits and is routinely used in clinical trials.²