Chapter 12 Dyschezia and Tenesmus

Definition

Dyschezia and tenesmus are clinical signs usually associated with colorectal disease. Dyschezia is the term applied to difficult or painful defecation, which is most commonly observed with anorectal disorders. Tenesmus is the clinical sign associated with straining to defecate (more common) or urinate (less common). Tenesmus is usually caused by large bowel disease, particularly colitis. Straining is usually evident as an animal maintaining a posture of defecation for an extended period, or as repeated, nonproductive attempts to defecate are observed. Tenesmus is often associated with other clinical signs of colonic disease including large bowel diarrhea (e.g., increased frequency of defecation, the production of scant fecal volume), hematochezia (fresh red blood on the feces), and/or excessive fecal mucus. Tenesmus is a clinical sign and not a disease; consequently, an underlying cause must be identified. In general, tenesmus and dyschezia are more commonly associated with colorectal disorders in dogs than in cats. Dysuria in cats with lower urinary tract disease may be misinterpreted as dyschezia and tenesmus.

Pathophysiology and Mechanisms

Inflammation of the colonic or rectal mucosa is the most common cause of tenesmus and dyschezia in dogs and cats.¹^–⁴ Tenesmus may also occur with colonic, rectal, or anal obstruction, and constipation. Dyschezia is usually caused by diseases involving anal and perianal structures.^3,⁴ Severity of inflammation causing tenesmus or dyschezia is generally dictated by the magnitude of the host immune response. For example, mucosal inflammation of colonic inflammatory bowel disease (IBD) may be explained by (a) aberrant host responses to the colonic microbiota and (b) disturbances in colonic motility.⁵ A generic inflammatory response involving infiltrating immune cells (e.g., B and T lymphocytes, macrophages), secretomotor neurons (e.g., vasoactive intestinal polypeptide, substance P), cytokines (both T-helper type 1 [Th]1 and Th2 derived), and various inflammatory mediators (e.g., leukotrienes, prostanoids, reactive oxygen species, and nitric oxide metabolites) drive the chronic inflammatory process.⁵ Inflammation can cause suppression of normal colonic motility patterns, which may contribute to onset and severity of clinical signs. Other factors that may contribute to large bowel signs include previous therapies (especially antibiotics), bacterial fermentation (e.g., short-chain fatty acids [SCFA], lactate) products, altered composition of the colonic microbiota, and perturbed mucus secretion.

Other inflammatory conditions causing tenesmus and dyschezia can include helminths (Trichuris spp., Ancylostoma spp.), protozoa (Giardia spp., Trichomonas spp.), fungi (Histoplasma spp.), oomycetes (Pythium spp.), algae (Prototheca spp.), bacteria (Campylobacter spp., Clostridia spp., enteropathogenic/enterotoxigenic Escherichia coli), colorectal tumors, and rectal/anal strictures.² Mechanism for mucosal inflammation with these disorders varies and includes local mucosal irritation (e.g., nematode parasites), robust host immune responses (e.g., histoplasmosis, pythiosis), and direct mucosal association (e.g., adherent and invasive E. coli [AIEC] as seen with granulomatous colitis).

Constipation is another important cause of tenesmus and dyschezia in animals.² Constipation is defined as difficult, reduced, or painful evacuation of feces that occurs secondary to colonic hypomotility or dysmotility disorders, mechanical obstruction, or colorectal diseases. Dry, hardened feces are difficult to pass, and chronically constipated cats have intermittent episodes of tenesmus, hematochezia, or diarrhea due to the mucosal irritant effect of impacted feces. Fiber-responsive colitis is a unique large bowel diarrheal syndrome of dogs in which altered colonic motility causes clinical signs of excessive fecal mucus, hematochezia, and tenesmus.

Urogenital disease may occasionally cause tenesmus in some animals as nonbacterial (e.g., feline lower urinary tract disease [FLUTD], neoplasia, calculi) and bacterial-mediated inflammation involving the urinary bladder, urethra, and genital organs (e.g., prostate) is relatively common in dogs and cats.

Differential Diagnosis

Box 12-1 presents causes for tenesmus and dyschezia in companion animals. Although diseases affecting colon and rectum are the predominant source of clinical signs, it is important to exclude disturbances in other organs (e.g., urogenital disease) that can also cause tenesmus. Cats are notorious for stranguria associated with FLUTD, which can confound accurate assessment of ineffective straining associated with colorectal disease. A thorough patient history and observation of the animal’s elimination process are essential for avoiding misdiagnosis.