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202 Constipation/Obstipation and Megacolon

• Allergic conjunctivitis may require long-term with intraocular diseases such as glaucoma Technician Tips
systemic therapy and/or the intermittent use or uveitis) by noting that conjunctival vessels A Schirmer tear test, tonometry, and fluorescein
VetBooks.ir ○ Dogs with medial canthal pocket syn- versus the larger diameter, nonbranching for a red eye.
of topical steroids.
staining should be done on any dog evaluated
have a small diameter and branching pattern
drome typically require intermittent or
episcleral vessels. Conjunctival vessels are
maintenance topical steroids.
also mobile and will blanch after the topical
application of phenylephrine or epinephrine; SUGGESTED READING
Hendrix DVH. Diseases and surgery of the canine
PROGNOSIS & OUTCOME episcleral vessels are nonmobile and do not conjunctiva and nictitating membrane. In Gelatt
blanch quickly after the application of topical KN, et al, editors: Veterinary ophthalmology, ed 5,
Most cases of isolated conjunctivitis due phenylephrine or epinephrine. Ames, Iowa, 2013, Wiley-Blackwell, pp 945-975.
to mechanical irritation or allergies resolve • Do not forget to check Schirmer tear AUTHOR: Nancy Johnstone McLean, DVM, DACVO
with topical corticosteroid therapy. However, test values when evaluating dogs for EDITOR: Diane V. H. Hendrix, DVM, DACVO
recurrences are common, and ongoing or conjunctivitis.
intermittent therapy may be indicated. • Avoid topical corticosteroids in cases of
corneal ulceration.
PEARLS & CONSIDERATIONS • Systemic steroids can cause recrudescence
of CHV-1 infection.
Comments
• Conjunctival hyperemia can be differentiated
from episcleral injection (usually associated

Constipation/Obstipation and Megacolon Client Education
Sheet

BASIC INFORMATION ASSOCIATED DISORDERS • Inflammation can be associated with con-
Perineal hernia may be the cause or result of stipation (perianal fistula, proctitis, anal sac
Definition constipation and megacolon. abscess, or perianal bite wounds).
• Constipation: infrequent or difficult Clinical Presentation • Water absorption from feces in colon results
evacuation of feces; does not imply loss of in concretion that is difficult or impossible
function DISEASE FORMS/SUBTYPES to pass (common in cats with chronic kidney
• Obstipation: intractable constipation • Hypertrophic megacolon: develops as a disease or diabetes mellitus).
• Megacolon: persistent dilation of the large consequence of obstructive lesions and may • Neurogenic dysfunction from dysautonomia
intestine associated with chronic constipa- be reversible with early therapy. (autonomic system failure), trauma to pelvic
tion or obstipation; may occur secondary to • Dilated megacolon: end stage of colonic or hypogastric nerves (pelvic fracture),
idiopathic loss of colon function. Dilated dysfunction (idiopathic or untreated neoplasia of spinal cord, or caudal spinal
megacolon implies permanent disruption hypertrophic megacolon) and may be poorly cord diseases (e.g., lumbosacral disease,
of colonic structure and loss of colonic responsive to treatment lumbosacral stenosis/cauda equina syndrome,
function. Manx cat sacral deformities)
HISTORY, CHIEF COMPLAINT • Prolonged distention of colon causes irrevers-
Epidemiology • Reduced, absent, or painful defecation is ible changes in colonic smooth muscles and
SPECIES, AGE, SEX typical. nerves.
Constipation: dogs and cats. Obstipation/ • Fecal balls are often very hard if passed; • Retained bacterial toxins may be absorbed,
megacolon may be more common in middle- occasionally, watery diarrhea may be passed resulting in endotoxemia and anorexia,
aged, male, domestic short-haired or long-haired around fecal concretion. lethargy, and/or vomiting.
or Siamese cats. Megacolon is rarely reported • Prolonged constipation will result in anorexia,
in dogs. lethargy, weight loss, or vomiting (may be DIAGNOSIS
projectile).
GENETICS, BREED PREDISPOSITION Diagnostic Overview
Manx cats may be predisposed to neurogenic PHYSICAL EXAM FINDINGS The diagnosis of constipation is based on a
megacolon. Congenital segmental aganglionosis • Poor body condition history of difficult, reduced, or absent defeca-
(Hirschsprung disease in humans) has been • Dehydration tion and finding firm feces in the colon on
documented in only one kitten. • Colon distended with hard feces on abdomi- abdominal palpation. Some underlying causes
nal palpation; signs of abdominal pain may can be determined by physical examination and
RISK FACTORS be present abdominal radiography.
• Intrinsic dysfunction that prevents passage • Perineal irritation/ulceration
of feces: spinal cord/spinal nerve disease or • Rectal exam (usually requires sedation Differential Diagnosis
trauma, dysautonomia in cats): hard feces, ± pelvic narrowing, Reversible causes of constipation:
• Mechanical obstruction that prevents passage ± stricture or mass palpated, ± perineal • Dehydration, electrolyte disorders, inflam-
of feces: pelvic fracture, colonic stricture or hernia matory diseases of the anorectum
neoplasia, extraluminal mass or stricture • Drug administration (opioids, anticholiner-
compressing colon, rectoanal stricture, Etiology and Pathophysiology gics)
colonic foreign body • Prolonged retention of feces in colon due • Environmental changes (inactivity, litter box
• A bony diet and low levels of exercise may to functional (neurogenic) or mechanical changes)
predispose dogs to megacolon. obstruction Any risk factors causing mechanical obstruction

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