Report From: WSAVA Gastrointestinal Standardization Group
Robert J. Washabau, VMD, PhD, DACVIM
Professor of Medicine and Department Chair, Department of Veterinary Clinical Sciences, College of Veterinary Medicine, University of Minnesota
St. Paul, MN, USA

Background

The WSAVA Gastrointestinal Standardization Group was initially developed to obtain a world-wide standard for the histological evaluation of gastrointestinal tract disease of cats and dogs. At the present time, a number of histological grading schemes have been proposed but none are universally accepted. Consequently, an intestinal biopsy sent to four different pathologists may result in four different biopsy reports. This is true of many gastrointestinal disorders (e.g., malignancy, toxicity, infection, lymphatic dilation, inflammation, villus atrophy), but it is particularly true of inflammatory bowel disease. The situation is further complicated by different nomenclatures for the same disease or disease severity in different parts of the world. With the support of the WSAVA, the Gastrointestinal Standardization Group has proposed to develop a standardized histologic evaluation system that will be applied to all companion animal gastroenterologic disorders. Standardization will yield several obvious benefits including uniform diagnosis of disease, staging of disease, and the subsequent development of controlled clinical trials for the treatment of canine and feline gastrointestinal disorders.

Membership of the Group

Study Group Participants

Name

Country

Affiliation

Discipline

E-Mail

Bilzer, Thomas

Germany

University of Dusseldorf

Pathology

Bilzer@uni-duesseldorf.de

Day, Michael

UK

University of Bristol

Pathology

M.J.Day@bristol.ac.uk

Guilford, Grant

New Zealand

Massey University

Internal Medicine

W.G.Guilford@massey.ac.nz

Hall, Edward

UK

University of Bristol

Internal Medicine

dred.hall@bristol.ac.uk

Jergens, Albert

USA

Iowa State University

Internal Medicine

ajergens@iastate.edu

Mansell, Joanne

USA

Texas A & M University

Pathology

jmansell@cvm.tamu.edu

Minami, Takeo

Japan

Pet-Vet, Yokahoma

Pathology

takeojp@pet-vet.or.jp

Washabau, Robert

USA

University of Minnesota

Internal Medicine

washabau@umn.edu

Wilcock, Brian

Canada

Univ. of Guelph/HistoVet

Pathology

wilcock@histovet.com

Willard, Michael

USA

Texas A & M University

Internal Medicine

mwillard@cvm.tamu.edu

WSAVA Officers

Brovida, Claudio

Italy

WSAVA

Nephrology

cbr@anubi.it

Varga, Gabriel

Slovak Republic

WSAVA

Medicine

varga@napri.sk

Goals of the Group

Gastrointestinal diagnosis in small animals (dogs and cats) has been fraught with many difficulties, particularly in the histologic interpretation of intestinal biopsies. What constitutes normal intestinal morphology is only now being determined, and the recognition of subtle abnormalities is quite challenging. Although a number of criteria can be applied in the examination of biopsy specimens, the interpretation by the histopathologist is often quite subjective. Discrepancies in biopsy reports between different pathologists is surprisingly common. Consequently, several groups (including the Comparative Gastroenterology Society, the European Society for Comparative Gastroenterology, and the American College of Veterinary Internal Medicine) have called for national and international efforts to standardize the histologic evaluation of the gastrointestinal tract of cats and dogs. The recent work of the WSAVA Liver Standardization Group has provided additional impetus and urgency to the need for standardization of the primary disorders of the gastrointestinal tract.

Specific Aims

1.  An international group of scholars was organized from the specialties of Veterinary Pathology and Internal Medicine to review gastrointestinal tract diseases of dogs and cats. Clinicians and pathologists have been reviewing major and minor diseases of the gastrointestinal tract with the aim of standardizing language and nomenclature that are applied to the histologic characterization and diagnosis of gastrointestinal disease. To accomplish these goals, the group will hold four or five meetings over a two- to three-year period. Histology slides are distributed among the pathologists for their interpretation three to four months in advance of each meeting, and the pathologists and clinicians review, discuss, revise, and re-classify gastrointestinal diseases during 1-2 day meetings over a multi-headed microscope.

2.  Members of the International Working Group were recruited from the ACVIM, ECVIM, and other international Specialty Colleges and universities.

3.  Meetings of the International Working Group are held at annual meetings of the ACVIM, ECVIM, and WSAVA for the purposes of elevating the visibility and stature of the Working Group in the eyes of the relevant International Specialty Colleges. (Many members of the Working Group are also likely to attend their own professional meeting, e.g., ACVIM Forum and ECVIM Congress.)

4.  The Group will report findings to Gastroenterology specialists in attendance at the annual meetings of the ACVIM and ECVIM during the two-year timeframe of the Working Group.

5.  After final consultation with other Gastroenterology specialists at the ACVIM and ECVIM annual meetings, the Group will develop and publish one or more Consensus Statements and other manuscripts in the pathology and internal medicine journals.

First Meeting of the Group

The Group held its first meeting on June 8 & 9, 2004 in St. Paul, Minnesota on the occasion of the 2004 ACVIM Forum in Minneapolis. The agenda for that meeting included problems in the interpretation of G.I. biopsies; gastric, intestinal, and colonic histopathology and immunopathology; problems and pitfalls in the diagnosis of IBD; gastrointestinal disease distribution; and, endoscopic standards and biopsy techniques.

The Need for Standardization

Following that meeting, the Group concluded that there is a great need for three types of standardization: histologic descriptions of gastrointestinal disease, the functional disorders (i.e., those disorders for which there are prominent gastrointestinal clinical signs but for which is there minimal to no histologic change), and each of the steps of a medical investigation. The latter standardization could include history taking, physical examination, laboratory tests including intermediate endpoint biomarkers, imaging procedures and reports, endoscopic procedures and reports, biopsy procedure, histopathology and biopsy reports, immunohistochemistry, treatment trials, and patient response/outcome.

Initial Working Groups

Inflammatory
Bowel Disease

Endoscopic
Standardization

Food Sensitivity
Reactions

Gastrointestinal
Neoplasia

Al Jergens

Mike Willard

Grant Guilford

Brian Wilcock

Ed Hall

Grant Guilford

Robert Washabau

Takeo Minami

Michael Day

Al Jergens

Mike Willard

Joanne Mansell

Joanne Mansell

Joanne Mansell

Michael Day

Thomas Bilzer

Thomas Bilzer

Ed Hall

Brian Wilcock

Robert Washabau

Second Meeting of the Group

The Standardization Group will hold its second meeting in Baltimore on May 31, 2005 on the occasion of the 2005 ACVIM Forum. The agenda for this meeting will include reviewing the progress of the subgroups working on endoscopic standardization, food sensitivity reactions, and gastrointestinal neoplasia; re-visiting plans for inflammatory bowel disease; and, entertaining a new proposal for validation of diagnostic tests.

New agendae--The Group is considering a specific proposal to derive guidelines for the validation of specialized gastrointestinal assays available to veterinary practices and veterinary laboratories. The Group would hope to establish criteria to define whether tests are certainly valid, probably valid, or if there is insufficient evidence to support their validity. Details of reference standards would be published for various analytes used in gastrointestinal diagnosis. Reference laboratories and assay companies would be able to cite the guidelines as standards to which they adhere.

Area of Interest--Canine Inflammatory Bowel Disease

Inflammatory bowel disease (IBD) may be defined using clinical, histologic, immunologic, pathophysiologic, and genetic criteria.

Clinical Criteria

IBD has been defined clinically as a spectrum of gastrointestinal disorders associated with chronic inflammation of the stomach, intestine and/or colon of unknown etiology.1 A clinical diagnosis of IBD is considered only if affected animals have: (1) persistent (>3 weeks in duration) gastrointestinal signs (anorexia, vomiting, weight loss, diarrhea, hematochezia, mucousy feces), (2) failure to respond to symptomatic therapies (parasiticides, antibiotics, gastrointestinal protectants) alone, (3) failure to document other causes of gastroenterocolitis by thorough diagnostic evaluation, and (4) histologic diagnosis of benign intestinal inflammation.2 Small bowel and large bowel forms of IBD have been reported in both dogs and cats, although large bowel IBD appears to be more prevalent in the dog.

Histologic Criteria

IBD has been defined histologically by the type of inflammatory infiltrate (neutrophilic, eosinophilic, lymphocytic, plasmacytic, granulomatous), associated mucosal pathology (villus atrophy, fusion, crypt collapse), distribution of the lesion (focal or generalized, superficial or deep), severity (mild, moderate, severe), mucosal thickness (mild, moderate, severe), and topography (gastric fundus, gastric antrum, duodenum, jejunum, ileum, cecum, ascending colon, descending colon).3 As with small intestinal IBD, subjective interpretation of large intestinal IBD lesions has made it difficult to compare tissue findings between pathologists. Subjectivity in histologic assessments has led to the development of several IBD grading systems.3-10

Immunologic Criteria

IBD has been defined immunologically by the innate and adaptive response of the mucosa to gastrointestinal antigens. Although the precise immunologic events of canine and feline IBD remain to be determined, a prevailing hypothesis for the development of IBD is the loss of immunologic tolerance to the normal bacterial flora or food antigens, leading to abnormal T cell immune reactivity in the gut microenvironment.11 Genetically engineered animal models (e.g., IL-2, IL-10, and T cell receptor knockouts) that develop IBD involve alterations in T cell development and/or function suggesting that T cell populations are responsible for the homeostatic regulation of mucosal immune responses.12 Immunohistochemical studies of canine IBD have demonstrated an increase in the T cell population of the lamina propria, including CD3+ cells and CD4+ cells, as well as macrophages, neutrophils, and IgA-containing plasma cells. Many of the immunologic features of canine IBD can be explained as an indirect consequence of mucosal T cell activation. Enterocytes are also likely involved in the immunopathogenesis of IBD. Enterocytes are capable of behaving as antigen-presenting cells, and interleukins (e.g., IL-7 and IL-15) produced by enterocytes during acute inflammation activate mucosal lymphocytes. Up-regulation of Toll-like receptor 4 (TLR4) and Toll-like receptor 2 (TLR2) expression contribute to the innate immune response of the colon.13 Thus, the pathogenesis and pathophysiology of IBD appears to involve the activation of a subset of CD4+ T cells within the intestinal epithelium that overproduce inflammatory cytokines with concomitant loss of a subset of CD4+ T cells, and their associated cytokines, which normally regulate the inflammatory response and protect the gut from injury. Enterocytes, behaving as antigen-presenting cells, contribute to the pathogenesis of this disease.14

Pathophysiologic Criteria

IBD may be defined pathophysiologically in terms of changes in transport, blood flow, and motility. The clinical signs of IBD, whether small or large bowel, have long been attributed to the pathophysiology of malabsorption and hypersecretion, but experimental models of canine IBD have instead related clinical signs to the emergence of abnormality motility patterns.

The pathophysiology of IBD is explained by at least two interdependent mechanisms: the mucosal immune response, and accompanying changes in motility.

Immune Responses--A generic inflammatory response involving cellular elements (B and T lymphocytes, plasma cells, macrophages, and dendritic cells), secretomotor neurons (e.g., VIP, substance P, and cholinergic neurons), cytokines and interleukins, and inflammatory mediators (e.g., leukotrienes, prostanoids, reactive oxygen metabolites, nitric oxide, 5-HT, IFN-γ, TNF-α, and platelet-activating factor) is typical of canine and feline inflammatory bowel disease.15,16 There are many similarities between the inflammatory response of the small and large intestine, but recent immunologic studies suggest that IBD of the canine small intestine is a mixed Th1/Th2 response1,17,18 whereas IBD of the canine colon may be more of a Th1 type response with elaboration of IL-2, IL-12, INF-γ, and TNF-α.19 Other studies of canine colonic IBD have demonstrated increased numbers of mucosal IgA- and IgG-containing cells,4,20-22 nitrate,21 CD3+ T cells, nitric oxide (NO),23 and inducible nitric oxide synthase (iNOS)23 in the inflamed colonic mucosa. Increases in the CD3+ positive T cell population of the inflamed colon are consistent with changes reported in the inflamed canine intestine. Thus, there are important similarities and differences between small and large bowel IBD.

Motility Changes--Experimental studies of canine large intestinal IBD have shown that many of the clinical signs (diarrhea, passage of mucus and blood, abdominal pain, tenesmus, and urgency of defecation) are related to motor abnormalities of the colon. Ethanol and acetic acid perfusion of the canine colon induces a large bowel form of IBD syndrome indistinguishable from the natural condition.24,25 Inflammation in this model suppresses the normal phasic contractions of the colon, including the migrating motility complex, and triggers the emergence of giant migrating contractions (GMCs). The appearance of these GMCs in association with inflammation is a major factor in producing diarrhea, abdominal cramping, and urgency of defecation. GMCs are powerful lumen-occluding contractions that rapidly propel pancreatic, biliary, and intestinal secretions in the fasting state, and undigested food in the fed state, to the colon to increase its osmotic load.26-28 Malabsorption results from direct injury to the epithelial cells and from ultrarapid propulsion of intestinal contents by giant migrating contractions (GMCs) so that sufficient mucosal contact time is not allowed for digestion and absorption to take place.

Inflammation impairs the regulation of the colonic motility patterns at several levels, i.e., enteric neurons, interstitial cells of Cajal, and circular smooth muscle cells.Inflammation suppresses the generation of tone and phasic contractions in the circular smooth muscle cells through multiple molecular mechanisms. Inflammation shifts muscarinic receptor expression in circular smooth muscles from the M3 to the M2 subtype.29 This shift has the effect of reducing the overall contractility of the smooth muscle cell. Inflammation also impairs calcium influx30 and down-regulates the expression of the L-type calcium channel31, which may be important in suppressing phasic contractions and tone while concurrently stimulating GMCs in the inflamed colon. Changes in the open-state probability of the large conductance calcium-activated potassium channels (KCa) partially attenuate this effect.32 Inflammation also modifies the signal transduction pathways of circular smooth muscle cells. Phospholipase A2 and protein kinase C (PKC) expression and activation are significantly altered by colonic inflammation33,34 and this may partially account for the suppression of tone and phasic contractions. PKC α, β, and ε isoenzyme expression is down-regulated, PKC ι and λ isoenzyme expression is up-regulated, and the cytosol-to-membrane translocation of PKC is impaired.34 The L-type calcium channel, already reduced in its expression, is one of the molecular targets of PKC. Inflammation also activates the transcription factor NF-κB which further suppresses cell contractility.35

Genetic Criteria

IBD may be defined by genetic criteria in several animal species. Crohn's disease and ulcerative colitis are more common in certain human genotypes, and a mutation in the NOD2 gene (nucleotide-binding oligomerization domain2) has been found in a sub-group of patients with Crohn's disease.14 Genetic influences have not yet been identified in canine or feline IBD, but certain breeds (e.g., German shepherds, Boxers) appear to be at increased risk for the disease.

References

1.  German AE, Hall EJ, Day MJ. Chronic intestinal inflammation and intestinal disease in dogs. J Vet Intern Med 17: 8, 2003.

2.  Jergens AE, Schreiner CA, Frank DE, et al. A scoring index for disease activity in canine inflammatory bowel disease. J Vet Intern Med 17: 291, 2003.

3.  Wilcock B. Endoscopic biopsy interpretation in canine or feline enterocolitis. Semin Vet Med Surg 7: 162, 1992.

4.  Spinato MT, Barker IK, Houston DM. A morphometric study of the canine colon: comparison of control dogs and cases of colonic disease. Can J Vet Res 54: 477, 1990.

5.  Leib MS, Roth L, Burkholder W, et al. Effect of commercial diets on the endoscopic and histologic appearance of the colon of normal dogs. J Am Anim Hosp Assoc 28: 527, 1992.

6.  Stonehewer J, Simpson JW, Else RW et al. (1998). Evaluation of B and T lymphocytes and plasma cells in colonic mucosa from healthy dogs and from dogs with inflammatory bowel disease. Res Vet Sci 65: 59, 1998.

7.  Roth L, Walton AM, Leib MS. Plasma cell populations in the colonic mucosa of clinically normal dogs. J Am Anim Hosp Assoc 28: 39, 1992.

8.  Van der Gaag I. The histologic appearance of large intestinal biopsies in dogs with clinical signs of large bowel disease. Can J Vet Res 52: 75, 1988.

9.  Van der Gaag I and Happe RP: Followup studies of large intestinal biopsies and necropsy in dogs with clinical signs of large bowel disease. Can J Vet Res 53: 473, 1989.

10. Roth L, Walton AM, Leib MS, et al. A grading system for lymphocytic-plasmacytic colitis in dogs. J Vet Diag Invest 2: 257, 1990.

11. Baumgart DC, McVay LD, and Carding SR. Mechanisms of immune cell-mediated tissue injury in inflammatory bowel disease. Int J Mol Med 1998; 1: 315.

12. Powrie F. T cells in inflammatory bowel disease. Immunity 1995; 3: 171-174. Hausmann, M., S. Kiessling, S. Mestermann, G. Webb, T. Spottl, T. Andus, J. Scholmerich, H. Herfarth,

13. K. Ray, W. Falk, and G. Rogler. 2002. Toll-like receptors 2 and 4 are up-regulated during intestinal inflammation. Gastroenterology 122:1987.

14. Bouma G, Strober W. The immunological and genetic basis of inflammatory bowel disease. Nature Reviews (Immunol) 3:521, 2003.

15. Elwood CM, Garden OA. Gastrointestinal immunity in health and disease. In Vet Clin N Amer - Small Anim Pract 29: 471, 1999.

16. Jergens AE. Inflammatory bowel disease. In Vet Clin N Amer - Small Anim Pract 29: 501, 1999.

17. German AJ, Helps CR, Hall EJ, et al. Cytokine mRNA expression in mucosal biopsies from German Shepherd dogs with small intestinal enteropathies. Dig Dis Sci 45: 7, 2000.

18. German AJ, Hall EJ, Day MJ. Immune cell populations within the duodenal mucosa of dogs with enteropathies. J Vet Intern Med 15: 14, 2001.

19. Ridyard AE, Nuttall TJ, Else RW, et al. Evaluation of Th1, Th2 and immunosuppressive cytokine mRNA expression within the colonic mucosa of dogs with idiopathic lymphocytic-plasmacytic colitis. Vet Immunol Immunopathol 86: 205, 2002.

20. Mayoral I, Pena L, Rodriguez-Franco F, et al. Immunohistological study of IgA, IgG and IgM in endoscopic biopsies of dogs with plasmacytic-lymphocytic colitis. Zentralbl Veterinarmed 43: 613, 1996.

21. Gunawardana SC, Jergens AE, Ahrens FA, et al. Colonic nitrate and immunoglobulin G concentrations in dogs with inflammatory bowel disease. J Amer Vet Med Assoc 211: 318, 1997.

22. Jergens AE, Gamet Y, Moore FM, et al. Colonic lymphocyte and plasma cell populations in dogs with lymphocytic- plasmacytic colitis: an immunohistochemical and morphometric study. Am J Vet Res 60: 515, 1999.

23. Jergens AE, Carpenter SL, Wannemuehler Y, et al. Molecular detection of inducible nitric oxide synthase in canine inflammatory bowel disease. J Vet Intern Med 12: 205 (abstract), 1998.

24. Sethi AK, Sarna SK. Colonic motor activity in acute colitis in conscious dogs. Gastroenterology 100: 954, 1991.

25. Sethi AK, Sarna SK. Colonic motor response to a meal in acute canine colitis. Gastroenterology 101: 1537, 1991.

26. Sarna SK, Condon R, Cowles V. Colonic migrating and nonmigrating motor complexes in dogs. Am J Physiol 246: G355, 1984.

27. Sarna SK, Prasad KR, Lang IM. Giant migrating contractions of the canine cecum. Am J Physiol 254: G595, 1988.

28. Sethi AK, Sarna SK. Contractile mechanisms of canine colonic propulsion. Am J Physiol 268: G530, 1995.

29. Jadcherla SR. Inflammation inhibits muscarinic signaling in vivo canine colonic circular smooth muscle cells. Pediatric Res 52: 756, 2002.

30. Shi XZ, Sarna SK. Impairment of calcium mobilization in circular muscle cells of the inflamed colon. Am J Physiol 278: G234, 2000.

31. Liu X, Rusch NJ, Striessnig J, et al. Down regulation of L-type calcium channels in inflamed circular smooth muscle cells of the canine colon. Gastroenterology 120: 480, 2001.

32. Lu G, Mazet B, Sun C, et al. Inflammatory modulation of calcium-activated potassium channels in canine colonic circular smooth muscle cells. Gastroenterology 116: 884, 1999.

33. Ali I, Campbell WB, Sarna SK. Impaired activation of cytosolic phospholipase A2 in the inflamed canine colonic circular muscle. Gastroenterology 119: 62, 2000.

34. Ali I, Sarna SK. Selective modulation of PKC isozymes by inflammation in canine colonic circular muscle cells. Gastroenterology 122: 483, 2002.

35. Shi XZ, Lindholm PF, Sarna SK. NF-kB activation by oxidative stress and inflammation suppresses contractility in colonic circular smooth muscle cells. Gastroenterology 124: 1369, 2003.

Speaker Information
(click the speaker's name to view other papers and abstracts submitted by this speaker)

Robert J. Washabau, VMD, PhD, DACVIM
College of Veterinary Medicine, University of Minnesota
St. Paul, MN


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