Section: Information In-depth
Causes
There are many causes of constipation. Although it is not unusual for a normal dog to have a bout or two of constipation over the course of their lives, it is not normal or acceptable for them to have recurring problems, hence, establishing an underlying cause should be attempted in these cases.
Dietary related factors are the most common cause for constipation in veterinary medicine. Foreign material, especially hair, bones, sticks, and sand can form hard masses that the dog has difficulty eliminating. In some cases, this material is retained, causing an inability to defecate and eventual obstipation. In addition, diets low in fiber may predispose to constipation.
Certain environmental factors may contribute to constipation. Limited exercise, limited access to water, and failure to provide the appropriate time and place for defecation may cause fecal retention and constipation.
Certain drugs, including antacids, Kaopectate, iron supplements, antihistamines, barium, and diuretics may cause constipation.
Painful defecation associated with anorectal disease (anal sacculitis or abscess, perianal fistula, stricture, rectal foreign body or tumor, or rectal prolapse) or trauma (fractured pelvis, limb, or back, laceration, bite wound).
Mechanical obstruction (something physically blocking the path of stool elimination) can be caused by extraluminal (from outside the colon wall) or intraluminal (from inside the colon wall) causes. Extraluminal disorders causing constipation include narrowed pelvic canal from a previous fracture, prostatic enlargement secondary to multiple prostatic disorders, sublumbar lymphadenopathy (enlarged lymph nodes above the colon), and rectal tumors. Intraluminal disorders include colonic or rectal tumors or polyps, rectal foreign bodies, strictures, diverticulum (outpouching of the colonic wall), perianal hernias, and rectal prolapse.
Neurologic disorders including paralysis, spinal cord disease, disc disease, rabies, lead toxicosis, dysautonomia (a hereditary condition), and idiopathic megacolon can all cause constipation.
Metabolic and endocrine disorders can cause constipation as they may impair normal transit through the colon. These include hyperparathyroidism (a disorder causing elevated calcium levels), hypothyroidism, and hypokalemia (decreased potassium), and renal (kidney) disease.
Constipation is relatively common in dogs. However, it must be differentiated from obstipation and megacolon. Obstipation is intractable (resistant to control) constipation, and megacolon is a condition of extreme dilation of the colon. Obstipated dogs or those with megacolon are always constipated; however, constipated animals are not always obstipated or have megacolon.
Constipation can occur in association with any disorder that impairs the passage of fecal material through the colon, slowing its transit time. This delay in transit allows the removal of additional salt and water from the feces, producing harder and drier stools.
Systemic signs of constipation vary. Feces can be retained for days before any deleterious effects are observed. Some animals may display mild signs, such as a slightly prolonged posture while defecating, and then produce a dry, firm stool. Others will have frequent or painful attempts to defecate with little or no fecal passage. Severely constipated patients often exhibit depression, weakness, lack of appetite, and vomiting. These animals are quite ill and may require hospitalization. It is important to establish a definitive diagnosis and cause, especially in the dog with recurrent constipation.
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