Diagnostic options for horses with recurrent colic (Proceedings)

Diagnosis and treatment of horses with colic have certainly improved in the last 20 years. However, horses with recurrent colic continue to be a diagnostic and often management challenge for both owners and veterinarians. Recurrent colic is typically defined as 3 or more episodes of transient or prolonged colic over a period of months or one year or more. The causes of recurrent colic are varied and can include parasites, gastric ulcers, sand accumulation, impactions, ileal hypertrophy, intermittent gas colic, enteroliths, intra- or extra-luminal masses resulting in partial obstructions, inflammatory bowel disease (such as eosinophilic enteritis or enterocolitis), colonic displacements, and many others. Although a definitive etiology cannot always be determined without exploratory surgery, many diagnostics are currently available to assist in determining the most likely cause.

Diagnostic evaluation

A complete history and thorough physical examination with laboratory analysis is indicated for horses with recurrent colic. The physical exam should include an oral examination to evaluate the horse's teeth. Horses in need of routine dental care may have difficulty chewing and can be predisposed to impactions. The physical examination should always include thorough thoracic and cardiac auscultation. Recurrent colic is typically considered abdominal in origin; however, rare cases of other disease within the thorax (pleuropneumonia, cardiac abnormalities, etc) may result in flank watching and the perception of colic signs. A complete blood cell count and biochemistry profile will evaluate red blood cells, white blood cell ceount, electrolytes, total protein, albumin, and liver and kidney values. The clinical sign of icterus may be seen with prolonged anorexia, hemolysis, and liver disease. If initial lab work is suggestion of liver disease, a serum bile acids concentration should be performed to assess liver function. Initial evaluation should also include a rectal palpation, and may include nasogastric intubation if the horse is actively displaying signs of colic. Evaluation of a fecal sample for parasites and a thorough discussion about the horse's deworming program, diet, and pasture management is also recommended. Suspending manure in a plastic rectal sleeve with water to test for sand can also be informative, but does not definitively diagnose the absence of sand or quantify the amount of sand if it is present.

If the initial evaluation has not revealed a likely cause for the colic episodes, additional diagnostic testing should be considered. Additional tests may include an abdominocentesis, endoscopy of the stomach and proximal duodenum, ultrasound examination of the abdomen, radiographs of the abdomen, and small intestinal and/or rectal biopsy. Abdominocentesis can be performed under light sedation with a local anesthetic (infiltration of 1-2 ml of subcutaneous lidocaine is recommended with a 25 gauge needle). A 2x2" area should be clipped and sterilely prepped approximately 3 cm caudal to the xyphoid and 1-2 cm to the right of midline. Sterile gloves should be worn for the procedure. An 18 gauge 1.5 inch needle or sterile teat canula may be utilized. This author prefers a teat canula, as an 18 gauge needle may not be long enough to allow to adequate sample collection. When a teat canula is utilized, a small stab incision should be made using a 15 blade scalpel prior to introduction of the teat canula. As the teat canula is advances, 2-3 "pops" will be felt as you advance through the muscle, abdominal wall, and peritoneum. Fluid should be collected in an EDTA tube for cytology, and red top for culture if peritonitis is suspected. Inflammation or infection within the abdomen can result in changes in the peritoneal fluid. Normal values for abdominocentesis are: total protein <2.5 g/dl, WBC < 5000-10,000 cells/uL. On cytology, neutrophils comprise approximately 40% of cells, the rest being lymphocytes, macrophage and peritoneal cells. With intestinal strangulation, the protein will increase first (in the first 1-2 hours) such that the fluid will be clear but more yellow. After 3-4 hours of strangulation, RBC will also leak, and the fluid will take on an orange color. Typically after about 6 hours, WBC will increase gradually, with the progression of intestinal necrosis.

Gastric ulcers are a common problem in performance horses, and have been reported in 66-93% of racehorses in training (Murray 1996, Hammond 1986, Vatistas 1999), 67% of endurance horses (Nieto 2004), and 58% of show horses (McClure 1999). Horses with equine gastric ulcer syndrome (EGUS) may exhibit poor performance, decreased appetite, weight loss, and recurrent mild to moderate signs of colic. Endoscopy of the esophagus, pylorus, and stomach in a fasted horse enables a definitive diagnosis of EGUS. Endoscopy can also facilitate small intestinal biopsy of the duodenum if an infiltrative process is suspected. Prior to endoscopy, feed should be withheld for 12 hours. Water may also be withheld for several hours prior to the exam; however, for endoscopy units with suction capability, this is typically not necessary.

Ultrasound examination of the abdominal cavity enables evaluation of visible portions of the kidneys, liver, spleen, and intestinal tract (stomach, small intestine, colon, small colon, cecum). Thickening of the intestinal walls (≥0.5 cm) can be identified in conditions such as right dorsal colitis and other infiltrative and/or inflammatory intestinal diseases. Ultrasound may also identify abnormal masses in the abdomen such as an abscess or neoplasia. Sand can often be visualized on ultrasound exam as well; however, abdominal radiographs are ideal for documenting the presence and amount of intestinal sand. Radiographs will also be valuable in determining if enteroliths (intestinal stones/concretions) are present.

Rectal biopsy has been utilized for determination of infiltrative intestinal disease. The procedure can be accomplished in the standing sedated horse, typically with a cervical biopsy forceps. Biopsy samples are typically obtained from the dorsolateral rectal mucosa, at approximately 11 or 1 o'clock. One gloved hand should identify and grasp the rectal mucosa, while the other hand can manipulate the biopsy forceps. Samples are typically submitted in formalin for histopathology. However, normal specimens do not rule out the presence of colonic lesions.

Despite all of the aforementioned examinations, diagnosis can unfortunately still be elusive in some cases of recurrent colic. With advances in diagnostic techniques and surgical procedures, additional options include standing laparoscopic surgery and abdominal exploratory under general anesthesia. In miniature horses, foals, and some ponies, CT scan and MRI may be available at select referral centers. Most CT and MRI units are not capable of abdominal scans on animals larger than 300 pounds. If an abnormality is identified with CT or MRI, surgery may still be required to correct the underlying problem. Fortunately, complications from abdominal surgery have diminished and success rates have improved considerably for horses that require surgical intervention. The exact prognosis will depend on the underlying cause.

Prognosis

In one study (Mair and Hillyer, EVJ 1997), causes of chronic colic included colonic impaction (31%), peritonitis (16%), no diagnosis (8%), enteritis/colitis (7%), colonic displacement/torsion (6%), lymphosarcoma (4%), and to lesser extent, intestinal adhesions, ileal obstructions, liver disease, cecal impactions, thromboembolic disease, and intussusceptions. Exploratory celiotomy is necessary in many cases to make a definitive diagnosis, but owners should be aware that some cases are not amenable to treatment. The prognosis for successful resolution is determined by the lesion, as for any type of colic, but is probably comparable to the prognosis for acute forms of colic. In some horses in which a specific cause is not found at surgery, clinical signs can persist after surgery, and usually dietary and management changes are recommended for these horses. Thorough evaluation and understanding of possible causes of the problem can assist the owner and veterinarian in determining the most likely etiology of the colic. Treatment and management of affected horses are most effective when they can be targeted at a specific established diagnosis.

References

Bell RJ, Mogg TD, Kingston JK. Equine gastric ulcer syndrome in adult horses: a review. NZ Vet Journal 2007 Feb; 55(1):p 1-12.

McClure SR, Carither DS, Gross SJ, and Murray MJ. Gastric ulcer development in horses in a simulated show or training environment. JAVMA 2005 Sep 1; 227(5): 775-777.

Merritt AM, Sanchez LC, Burrow JA, Church M, and Ludzia S. Effect of Gastrogard and three compounded oral omeprazole preparations on 24 h intragastric pH in gastrically cannulated mature horses. Equine Vet J 2003 Nov; 35(7): p 691-695.

Mair TS and Hilllyer MH. Chronic colic in the mature horse: A retrospective review of 106 cases. Equine Vet J 1997 Nov; 29(6): 415-420.