Constipation and Anorectal Diseases

Chapter 74 Constipation and Anorectal Diseases



Robert G. Sherding


The presenting signs of anorectal disease can include any of the following: dyschezia, hematochezia, constipation, anal discomfort (licking, scooting), ribbon-like feces, fecal incontinence, anal discharge, malodorous perineum, matting of perianal hair, and perianal dermatitis. Physical examination establishes the diagnosis of anorectal disease in most cases. In many anorectal diseases, surgery is required for effective treatment (see Chapter 75).



CONSTIPATION


Constipation is a clinical sign characterized by absent, infrequent, or difficult defecation associated with retention of feces within the colon and rectum. When feces are retained for a prolonged period of time, they become progressively harder and drier and, eventually, become impacted as the mucosa continues to absorb water from the fecal mass. Terms associated with constipation are defined below:


• Obstipation—A condition of intractable constipation in which the colon and rectum become so impacted with excessively hard feces that defecation cannot occur.

• Megacolon—A condition in which the colon becomes extremely and irreversibly dilated and hypomotile. Megacolon occurs most frequently in cats with idiopathic smooth muscle dysfunction that leads to severe colonic dilation, recurrent constipation, and obstipation. Megacolon also can occur in both dogs and cats secondary to chronic colorectal obstruction.

• Dyschezia—A clinical sign often associated with constipation, characterized by difficult or painful evacuation of feces from the rectum and usually associated with lesions in or near the anal region.

• Tenesmus—A clinical sign characterized by straining to defecate, usually ineffectively or painfully; thus, it often accompanies dyschezia.


Etiology


Underlying causes and predisposing factors for constipation are listed in Table 74-1 and include dietary factors, environmental factors, painful defecation, anorectal or colonic obstruction, neuromuscular diseases, fluid and electrolyte disturbances, and drug-related effects.


Table 74-1 CLASSIFICATION AND CAUSES OF CONSTIPATION



















































































































Category Cause
Dietary factors Ingested foreign material mixed with feces (hair, bones, cloth, garbage, cat litter, stones, wood, plant material)
Inadequate water intake
Environmental/psychological factors Dirty litter box
Prolonged inactivity
Confinement (hospitalization, boarding)
Change in habitat or daily routine
Painful defecation Anorectal disorders
  Anal sac impaction, infection, or abscess
Anorectal stricture, tumor, or foreign body
Myiasis
Perianal fistulae
Perianal bite wound cellulitis or abscess
Pseudocoprostasis
Orthopedic disorders
  Spinal disease or injury
Injuries of the pelvis, hip joints, or pelvic limbs
Rectocolonic obstruction Extramural
  Prostatic hypertrophy, tumor, abscess, or prostatitis
Paraprostatic cyst
Pelvic fracture (malunion)
Pelvic collapse due to nutritional bone disease
Perianal tumor
Pseudocoprostasis
Intramural or intraluminal
  Rectocolonic stricture, tumor, or foreign body
Perineal hernia or rectal diverticulum
Rectal prolapse
Fecalith
Neuromuscular dysfunction Lumbosacral spinal cord disease (injury, deformity, degeneration, neoplasia)
Bilateral pelvic nerve injury
Dysautonomia (Key-Gaskell syndrome)
Hypothyroidism
Idiopathic megacolon
Fluid and electrolyte abnormalities Dehydration (e.g., chronic renal disease)
Hypokalemia
Hypercalcemia (hyperparathyroidism, etc.)
Drug-induced effects Anticholinergics
Adrenergic antagonists
Calcium channel blockers
Phenothiazines and benzodiazepines
Opiates and opioids
Diuretics
Antihistamines
Aluminum hydroxide antacids
Sucralfate
Kaolin-pectin
Barium sulfate
Iron
Laxatives (abuse or chronic overuse)


Ingestion of Foreign Material


Ingested foreign material, such as indigestible fibrous material (especially hair in cats from their grooming behavior) and abrasives (especially bones in dogs), may become incorporated in the fecal mass and result in the formation of hard fecal impactions that are difficult and painful to evacuate from the colon.



Environmental Conditions


Environmental conditions that are not conducive to defecation or that vary from the daily routine to which a pet is accustomed may cause the pet to inhibit the urge to defecate, leading to constipation. This occurs, for example, when the pet is kept in strange surroundings, such as in a kennel or veterinary hospital, or when its daily outdoor exercise routine is changed. Indoor cats may suppress the urge to defecate when their litter box is too dirty or there is territorial competition with other cats in the household.



Painful Defecation


Painful anorectal diseases (anal sacculitis, perianal fistulas) and painful orthopedic disorders that limit positioning for defecation (diseases of the pelvis, spine, or hips) may result in voluntary inhibition of defecation and lead to constipation.



Rectocolonic Obstruction


Anorectal or colonic obstruction that mechanically impedes the passage of feces may result from intraluminal causes, such as foreign bodies, perineal hernia, and stenosing neoplastic or inflammatory lesions, or from extraluminal causes, such as prostatic enlargement, paraprostatic cysts, compressive pelvic fractures, perianal tumors, and pseudocoprostasis (feces matted in perianal hair).



Neuromuscular Disease


Neuromuscular disorders may lead to constipation by interfering with colonic innervation or smooth muscle function or with the ability of the animal to assume the normal defecation stance. For example, this may occur in association with disease or injury of the lumbosacral spinal cord (canine intervertebral disc disease), spinal deformity (e.g., Manx cats), endocrine disease (hypothyroidism), and dysautonomia, a progressive fatal autonomic polyneuropathy. When innervation of the anus is also impaired, fecal incontinence may be an associated clinical sign.


The pathogenesis of idiopathic megacolon involves a primary or secondary dysfunction of colonic smooth muscle (see later under “Megacolon”).



Fluid and Electrolyte Disorders


Dehydration can cause the feces to become excessively dry and hard, predisposing the animal to constipation. Hypokalemia and hypercalcemia can impair colonic smooth muscle function. A combination of these may explain the frequent constipation seen in chronic renal failure, especially in cats.



Drug-Related Constipation


Drug-induced constipation may be a side effect of motility-modifying drugs (anticholinergics, opiates, loperamide), antihistamines, barium sulfate, aluminum hydroxide, and diuretics.



Clinical Signs



• Reduced or absent defecation: Constipated animals are usually presented because of failure to defecate over a period of days. The owner may notice tenesmus or frequent attempts to defecate with little or no passage of feces. Constipation tends to be a recurrent problem in some patients, especially in cats.

• Dyschezia: Difficult or painful defecation usually indicates anorectal disease. The animal first may cry out as it attempts to defecate, usually with straining (tenesmus) during the attempt; then it may cease the effort, walk around anxiously, and repeatedly try again.

• Abdominal discomfort: Constipated animals may develop a hunched-up appearance.

• Paradoxical diarrhea: Mucosal irritation caused by impacted feces may provoke a secretion of fluid and mucus, which passes around the retained fecal mass and is expelled paradoxically as diarrhea during attempts to defecate.

• Other signs: Prolonged constipation may lead to anorexia, weight loss, lethargy, vomiting, and dehydration.


Diagnosis




Key Point


The presence of constipation usually is determined from the history and confirmed by rectal and abdominal palpation of colonic distention with hard, impacted feces. The goal of diagnosis is to identify predisposing factors (see Table 74-1).



• Use abdominal radiography to confirm constipation, assess the degree of colonic impaction with feces, and identify megacolon.

• Depending on severity and clinical signs, consider serum chemistries, neurologic examination, neurodiagnostics, abdominal ultrasonography, contrast barium enema radiography, and colonoscopy to identify underlying causes of constipation or predisposing factors. Diagnostics are indicated when constipation is recurrent.


History


Question the owner to identify the potential dietary, environmental, behavioral, psychological, and medication-related factors or predispositions listed in Table 74-1.



Physical Examination



• Perform a digital anorectal examination to detect painful or obstructive lesions of the anorectal area and pelvic canal. Sedation may be required.

• Evaluate the pelvic limbs, coxofemoral joints, pelvis, and lumbosacral spine for orthopedic problems that could cause painful defecation or difficulty maneuvering into position for defecation.

• Perform a neurologic examination (see Chapter 125) to identify underlying neurologic deficits that may be involved in causing constipation.

• In cats with constipation caused by dysautonomia (Key-Gaskell syndrome), additional manifestations of progressive autonomic failure that may be seen include urinary and fecal incontinence, megaesophagus, bradycardia, mydriasis, decreased lacrimation, and prolapse of the nictitating membranes.


Routine Laboratory Evaluations


Perform a serum biochemical profile, urinalysis, and complete blood count (CBC) in animals with recurrent constipation or during an episode of severe obstipation.



• This may identify underlying systemic disease that could cause constipation related to dehydration or electrolyte disturbances (e.g., chronic renal failure).

• In severely obstipated animals, especially those that are vomiting and depressed, this detects the metabolic consequences of prolonged fecal retention (e.g., fluid and electrolyte imbalances, endotoxemia, and azotemia) and guides supportive treatment.


Abdominal Radiography


Perform abdominal radiography to determine the following:


• Confirm the extent of colonic impaction with densely packed feces

• Identify the extreme dilation of the colon that indicates megacolon

• Identify radiopaque foreign material (e.g., bone chips) in the retained feces that indicates a dietary cause of constipation

• Identify pelvic, coxofemoral, or spinal lesions that can cause constipation

• Identify underlying prostatic enlargement that might cause constipation


Other Diagnostic Evaluations


These diagnostics may be warranted in selected patients with recurrent constipation:


• Thyroid function testing—Evaluate thyroid function in dogs with recurrent constipation and other signs compatible with hypothyroidism (see Chapter 31).

• Abdominal ultrasonography—Use this to evaluate the urogenital tract when prostatic disease, paraprostatic cyst, or pelvic canal neoplasia is suspected.

• Barium enema contrast radiography—Use this to evaluate the lumen of the colon when an intraluminal obstructive lesion is suspected (e.g., rectal stricture or neoplasia).

• Colonoscopy—Use this to evaluate the lumen of the colon after all retained feces have been removed.

• Neurodiagnostic evaluations—Use myelography, magnetic resonance imaging (MRI), electromyography, and nerve conduction studies to evaluate the lumbosacral spinal cord and spinal nerves in selected patients in which impaired anorectal innervation is suspected (see Chapter 125).


Treatment Overview


Simple constipation with mild to moderate impaction of feces and without systemic signs (depression, vomiting, dehydration) can be managed on an outpatient basis using rectal suppositories or oral laxatives combined with dietary modification and measures to enhance water intake. Oral laxatives can be prescribed (see a later section) and the patient can be reevaluated after 48 hours.


Severe constipation and obstipation may initially require evacuation of impacted feces from the colon (using enemas, manual extraction, or both) with correction of complicating dehydration and electrolyte imbalances.



• The subsequent goals of therapy are to eliminate or control any of the underlying causes of constipation (see Table 74-1) that are identified and to prevent recurrences using dietary modification, laxatives, and promotility agents as needed.

• Surgical correction is required for obstructing neoplasms, strictures, pelvic malunions, and anorectal diseases.

• Subtotal colectomy is often the most effective way to manage cats with advanced megacolon and recurrent obstipation that are unresponsive to medical therapy (see Chapter 70).


Initial Relief of Constipation


Use rectal suppositories, enemas, or manual extraction under anesthesia to initially relieve constipation.



Rectal Suppositories


To promote defecation in patients with mild constipation, give one to three pediatric rectal suppositories of docusate, glycerin, or bisacodyl. Rectal suppositories can be used alone or in combination with an oral laxative (Table 74-2). Pet and owner compliance are often limiting factors with suppositories.


Table 74-2 LAXATIVE THERAPY FOR CONSTIPATION














































































































































Treatment Product (Manufacturer) Dosage Regimen
Oral Laxatives
Bulk-Forming Laxatives
Psyllium Metamucil (Searle) 1–5tsp daily with food
Unprocessed whole grain and bran cereal Fiber One (General Mills) and others 1–5tbsp daily with food
Canned pumpkin Pie filling (Libby) 1–5tbsp daily with food
Commercial high-fiber diet Many Use as daily food source
Lubricant Laxatives
White petrolatum Laxatone (Evsco) 1–5 ml daily PO
Mineral oil* Many Not recommended
Emollient Laxatives
Docusate sodium Colace (Shire) Cat: 50 mg daily PO
Dog: 50–200 mg daily PO
Docusate calcium Surfak (Geneva) Cat: 50–100 mg daily PO
Dog: 100–240 mg daily PO
Osmotic Laxatives
Lactulose Duphalac Syrup (Reid-Powell), Cephulac (Marion Merrell Dow) 0.5–1.0 ml/kg q8–12h PO
Magnesium hydroxide Phillips Milk of Magnesia (Glenbrook) 2–8 tablets daily PO
Polyethylene glycol and electrolytes† Colyte (Schwarz), GoLytely (Braintree) 25–40 ml/kg PO, repeat in 2–4 hours (for bowel prep)
Stimulant Laxatives
Bisacodyl Dulcolax (Boehringer Ingelheim) Cat: 5 mg daily PO
Dog: 5–20 mg daily PO
Senna Senokot (Purdue Frederick) 1–4 tablets q12–24h PO
Castor oil† Many 5–30 ml PO (bowel prep)
Promotility Drugs
Cisapride Compounded pharmaceutical Cat: 1.0 mg/kg q8h or 1.5 mg/kg q12h PO
Dog: 0.25–0.5 mg/kg q8–12h PO
Tegaserod Zelnorm (Novartis) 0.05–0.1 mg/kg q12h PO
Ranitidine Zantac (Glaxo) Cat: 3.5 mg/kg q12h PO
Dog: 2.0 mg/kg q12h PO
Nizatidine Axid (Eli Lilly) 2.5 mg/kg q24h PO
Rectal Suppositories
Glycerin Many 1–3 pediatric
Docusate sodium Colace (Shire) 1–3 pediatric
Bisacodyl Dulcolax (Boehringer Ingelheim) 1–3 pediatric
Enemas
Isotonic saline solution (or tap water) 5–10 ml/kg
Lactulose Duphaloc, Cephulac (see above) 5–30 ml
Docusate sodium Colace (Shire) 5–30 ml
Mineral oil Many 5–30 ml or 1–2 ml/kg
Sodium phosphate‡ Fleet Children’s Enema (Fleet) 1–2 ml/kg or 1 enema unit
Bisacodyl Fleet Bisacodyl Enema (Fleet) 1–2 ml/kg or 1 enema unit

* Caution: May cause lipid aspiration pneumonia and may interfere with absorption of fat-soluble vitamins; combination with docusate may cause undesirable absorption of mineral oil.


† Used mainly to prepare the colon for radiography or endoscopy.


‡ Do not use in cats or small dogs.



• Docusate rectal suppository: An emollient (stool softener) laxative

• Glycerin: A lubricant laxative

• Bisacodyl: A stimulant laxative


Enema Therapy


Enema solutions are used to soften hard, impacted feces and promote evacuation. Warm the enema solution prior to instillation and use a lubricated rubber catheter or feeding tube to administer the calculated dose slowly so as not to induce vomiting. Commonly used enema solutions (see Table 74-2) include the following:


• Warm isotonic saline or tap water (5-10 ml/kg of body weight)

• Lactulose as an osmotic stool softener

• Docusate as an emollient (stool softener)

• Mineral oil as a lubricant



Key Point


Do not mix mineral oil and docusate. Docusate promotes mucosal absorption of mineral oil, and mineral oil coats the feces, preventing the emollient effect of docusate.



• Sodium phosphate solution, which has softening, bulk-producing, and irritant effects, can only be used in medium-sized and large dogs with normal hydration and renal function



Key Point


Caution! Never use phosphate enemas in cats or small dogs because of life-threatening hypernatremia, hyperosmolality, hyperphosphatemia, and hypocalcemia.



Manual Extraction of Impacted Feces


In severe constipation or obstipation, restore fluid and electrolyte balance parenterally and evacuate the colon manually under general anesthesia with endotracheal tube in place.



• Use colonic irrigation with warm isotonic saline as an enema solution to soften the impacted feces.

• Extract retained fecal masses by gentle transabdominal manipulation to milk the feces into the distal rectum for digital or forceps removal (using a sponge or whelping forceps).

• To avoid excessive bowel trauma in animals with extensive fecal impaction, it may be advisable to evacuate the colon manually in stages over 2 to 3 days.

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Aug 27, 2016 | Posted by in SMALL ANIMAL | Comments Off on Constipation and Anorectal Diseases

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