Views conclusions in ultrasound study as unsupported
This letter is in response to the article by Dr. Abutarbush (JAVMA, February 1, 2006, pp 409–413), wherein he introduces an ultra-sound sign for large colon volvulus (LCV). Unfortunately, we feel that the author makes assertions that are not supported by the study design or by the nature of the presentation of LCV in horses.
The author states, “This [ultrasound] method should … provide horse owners with a more accurate diagnosis and prognosis.…” Though a descriptive report is appropriate to introduce new ideas, it provides weak evidence for whether a diagnostic test is accurate. Therefore, this statement is not justified. The author describes four horses with LCV, but there was no hypothesis testing or statistical analysis performed, and there were no controls. Also, there is no mention of the difference between strangulating and nonstrangulating lesions of the large colon, which is considered the main factor in determining prognosis.1–4 Although Dr. Abutarbush acknowledges the new test needs evaluation of sensitivity and specificity, we find some of the conclusions far-reaching and potentially misleading.
Most of the confusion centers on the author's use of the term LCV. It is important to further differentiate an LCV as nonstrangulating or strangulating because the two conditions are associated with different survival rates and treatments.2–4 A nonstrangulating LCV of 180° or less (which also may be called a displacement) has a surgical survival rate of approximately 90%.4 A strangulating LCV of 360° or greater is considered a surgical emergency with a 50% survival rate.3,4 Dr. Abutarbush states, “In that study [Pease et al1], only horses with colic that required surgical treatment were included and not the general population of horses with colic, which reduces the value of this procedure to practitioners.” One of the guiding principles of evaluating the accuracy of a diagnostic test is that the test should assess a sample population that is representative of the target patient population. Since all strangulating LCV are surgical emergencies, we believe that the correct population is horses with large colon colic for which surgery is recommended, not the general population of horses with colic. Furthermore, the horses in Abutarbush's article all required surgery or euthanasia. Thus, the author did not evaluate the usefulness of the test in a sample population representative of the stated target patient population (ie, general population of horses with colic).
Another concern raised was that increased wall thickness may be confused with colitis if inflammation is severe and diffuse. Affected horses may have severe abdominal pain, large colon distention, and hypovolemia; however, the blood work and physical examination findings are usually not similar enough for horses with these two diseases to be confused clinically.
Our purpose is to inform readers that although sacculations can be detected with ultrasonography, it is the presence of vascular compromise and edema that should guide the practitioner to determine whether a horse requires immediate surgery as well as the prognosis for survival.1,3
Anthony Pease, DVM, MS, DACVR
Vanessa Cook, MA, VetMB, MS, DACVS, DACVECC
Samuel Jones, DVM, PhD, DACVIM
Anthony Blikslager, DVM, PhD, DACVS
North Carolina State University, Raleigh, NC
Peter Scrivani, DVM, DACVR
Hollis Erb, DVM, PhD
Cornell University, Ithaca, NY
- 1.↑
Pease AP, Scrivani PV, Erb HN, et al. Accuracy of increased large-intestine wall thickness during ultrasonography for diagnosing large-colon torsion in 42 horses. Vet Radiol Ultrasound 2004;45:220–224.
- 2.
Doran R, Allen D, Orsini J. Large intestine. In: Auer J, ed. Equine surgery. Philadelphia: WB Saunders Co, 1992; 395–397.
- 3.
Barclay WP, Foerner JJ, Phillips TN. Volvulus of the large colon in the horse. J Am Vet Med Assoc 1980;177:629–630.
- 4.↑
Phillips TJ, Walmsley JP. Retrospective analysis of the results of 151 exploratory laparotomies in horses with gastrointestinal disease. Equine Vet J 1993;25: 427–431.
The author responds
Thank you for the opportunity to respond to the comments of Dr. Pease et al. I regret that my article resulted in confusion and misunderstanding with regard to the structure, aim, and facts provided. Contrary to their opinions, all facts and conclusions contained in this paper are well documented by photographs and diagrams, where appropriate.
The aim of the study was to improve the methods for diagnosis of large colon volvulus (LCV), regardless of the type, and not further classify it nor provide a prognosis. Whether the degree of rotation is less or more than 180° (nonstrangulating or strangulating), it is by definition an LCV.1 I also documented that ultrasonography has the potential to localize the level at which rotation of the large colon occurred. I suggested that the method can provide a more accurate diagnosis and prognosis because it can reveal the length of affected intestine. This is supported by the fact that removal of greater than half of the large colon typically results in a survival rate of 53%, whereas removal of less than half results in a survival rate of 81%.2
Although it was not the focus of the study, my colleagues may underestimate the importance of 180° LCV. In one study,1 only 14 of 29 (48%) horses survived a 180° LCV, which is dramatically different from a survival rate of 90%.
Making an accurate diagnosis of the cause of intestinal obstruction in a horse with colic can be difficult if only physical examination findings are used. My article documents that ultrasonographic identification of large colon sacculations can be used to confirm the presence of LCV. If the thickness of the wall of the large colon is the only finding used to diagnose LCV, other causes of increased thickness of the large colon (such as colitis) will be misdiagnosed. I do not believe that blood work can accurately differentiate between peracute colitis and LCV. Colitis is common and can induce a thickened wall as visualized by ultrasonography.
The article does not contain any statistical analysis, nor does it need any. The JAVMA Instructions for Authors states that “a descriptive report does not typically contain statistical analysis,” and additionally, statistical analysis would have been inappropriate because of the small number of animals used. Ultrasonography is done routinely in the population (horses with colic) from which I elected to report only relevant cases to illustrate the point that ultrasonography can be used to diagnose LCV. The absence of sacculations will alert the examiner to the presence of an LCV.
I wonder about the wisdom of advising practitioners to wait until vascular compromise happens to the large colon before performing surgery in a horse in which LCV is diagnosed or highly suspected. Waiting to see signs of vascular compromise could be a regrettable and fatal mistake.
Sameeh M. Abutarbush, BVSc, MVetSc, DABVP, DACVIM
Atlantic Veterinary College University of Prince Edward Island Charlottetown, PE, Canada
Sees cover art birds as unhealthy
The painting on the cover of the January 15, 2006, JAVMA is a sad example of a far too common oversight by artists, magazines, brochure producers, bird product manufactures, and veterinary conference promoters.
In “Three Amigos,” the two lower positioned birds appear to have typical problems seen with malnourishment of captive parrots fed seed diets. They are overweight, are malcolored, and have overgrown beaks. The one lower bird has evidence of severe feather picking over its shoulders. The covert feathers have been plucked, and the down feathers remain. This is not a condition ever reported in the wild. Some birds with feather dystrophy caused by circovirus infection have been reported, but they were not feather picked or obese.1
I doubt that the AVMA would ever reproduce a painting of a mange-ridden dog with two show dogs on the JAVMA cover; yet, the gross abnormality in the birds portrayed on the January 15, 2006, cover was not mentioned.
Greg J. Harrison, DVM, DABVP emeritus Palm Beach, Fla
McOrist S, Black DG, Pass DA, et al. Beak and feather dystrophy in wild sulphur-crested cockatoos (Cacatua galerita). J Wildl Dis 1984;20:120–124.