Primary chronic constipation has been divided into three pathophysiological subtypes: (1) slow-transit constipation, (2) dyssynergic defecation, and (3) normal-transit constipation. There is a significant overlap among different types of constipation, and symptoms alone cannot differentiate the various types.

Slow-transit constipation, also known as colonic inertia, is the diagnosis when the measured colonic transit time is prolonged. This type of constipation most commonly occurs in young women who present with infrequent defecation and bloating.

Dyssynergic defecation is also known as pelvic floor dys-synergia, obstructed defecation, outlet obstruction, or anismus. It is caused by a lack of coordination between the abdominal and pelvic floor muscles during defecation, which leads to an inability to defecate. This condition often results in a feeling of anal blockage, severe straining, and the need to remove impacted stool. However, symptoms alone cannot be used to diagnose dyssynergic defecation. Both symptoms and physiological tests are required to make a diagnosis.

Patients with normal-transit (functional) constipation have normal colonic transit times and normal pelvic-floor function. This is the most prevalent of all chronic constipation sub-types. Abdominal pain and bloating can be present. Patients with constipation-predominant irritable bowel syndrome (IBS-C) experience a normal transit time, and it can be difficult to differentiate functional constipation from IBS-C.
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Although there is a significant overlap in symptoms between the three subtypes, identifying the predominant cause of chronic constipation is highly useful, because treatment strategies vary.