Research Update: Portosystemic shunts in dogs: Can medical therapy allow a delay in surgical intervention?

Most recent studies of dogs with congenital portosystemic shunts have investigated the relative efficacy and survival rates of novel surgical interventions. Although medical therapy can be attempted and the relative success at resolution of clinical signs and selected biochemical and histopathologic abnormalities have been compared,1 the survival times of dogs treated with medical therapy vs. dogs treated with surgery have not been compared. If medical management were to result in similar survival times as surgery, then veterinarians could more confidently offer this modality to owners of patients that are unable to tolerate the risks associated with surgery or when expense is a limiting factor. Conversely, differences in survival times may allow owners who are considering avoiding surgery to make more fully informed decisions as to the predicted lifespan of their pets. The authors of a new prospective study of dogs with single portosystemic shunts hypothesized that surgical vs. medical treatment would result in different survival times and that this difference may be influenced by shunt location.

WALTER B. MCKENZIE/GETTY IMAGES

This multicenter study compared short-term outcome and long-term survival of 126 dogs with a single congenital portosystemic shunt and associated clinical signs.2 Treatment options were discussed with each dog owner at the time of diagnosis. Based on the recommendation of the attending clinician and financial considerations, owners ultimately decided whether medical or surgical treatment would be attempted; patients were not randomly distributed into the two treatment groups. Various surgical procedures were used for partial or complete shunt ligation depending on surgeon preference, and these procedures' influence on survival was not evaluated separately. Medical management was not standardized but typically consisted of some combination of oral antibiotics, a modified protein diet, and lactulose.

The final study population included 99 surgically treated dogs and 27 dogs that had been medically managed. Despite the lack of randomization, no statistical differences existed between the two groups in regards to age at diagnosis (which has previously been identified as a prognostic indicator in dogs with portosystemic shunts),3 sex, or the proportion of dogs with intrahepatic or extrahepatic portosystemic shunts. Complete shunt ligation (39.4%) and the placement of ameroid ring constrictors (29.2%) were the most common surgical interventions.

At the time of data collection, 14 of 27 (51.9%) medically managed dogs and 87 of 99 (87.9%) surgically treated dogs were still alive. When considering dogs that had died and those still alive at the time of study termination, survival time was > 3 years for 60% of medically treated dogs and 80% of surgically treated dogs. This difference was significant, with medically treated dogs having a greater likelihood of dying, particularly in the first two or three years after diagnosis, based on Kaplan-Meier survival graphs. The age of the dogs at the time of diagnosis and the shunt location were not significantly associated with survival. Five of 99 (5.1%) surgically treated dogs died of complications secondary to their surgical procedures; however, deaths associated with the portosystemic shunt but unrelated to the surgical procedure were more common in medically treated dogs (8 of 27 [29.6%]) than in surgically treated dogs. Thus, this study's results show that while both surgical and medical management may result in long-term survival in a subset of dogs, surgical treatment is associated with improved survival in the first three years and with overall significantly longer survival times.

COMMENTARY

Although not systematically studied, the presumptive reasons for the referral of dogs with portosystemic shunts are likely multifactorial, including the need for intensive management of severe preoperative hepatic encephalopathy, the technical expertise required for surgical correction, and the fear of severe complications during the immediate postoperative period. It is possible that based on the expense associated with these management and surgical considerations some dogs are euthanized rather than being referred for surgery. This study's results provide owners and veterinarians additional information on the expected short- and long-term survival of medically managed dogs. Although surgery was definitively associated with a longer survival time after diagnosis, a median survival time > 3 years was still achieved in many dogs with medical therapy alone.

In this study, the authors failed to find that a dog's age at the time of diagnosis affected survival, which had been shown to be important in a previous publication specifically evaluating medically managed dogs.3 Based on this finding, the authors conclude that surgical intervention could potentially be delayed in some dogs in favor of medical therapy if circumstances do not allow for immediate referral. However, this conclusion requires further study. In this study, most dogs underwent surgical intervention immediately after diagnosis rather than after a delayed period associated with medical management. Future studies should compare the survival times associated with immediate vs. delayed surgical intervention before veterinarians confidently recommend that owners can attempt medical therapy without later consequences.

The authors acknowledge that their nonrandomized study design may have led to marked bias and, therefore, potentially inaccurate results. As mentioned, clients were allowed to select the final treatment plan for their dogs, and recommendations made by the various surgeons were likely influenced by their personal success with surgical vs. medical therapy of portosystemic shunts, the severity of clinical signs in each particular dog, and the shunt location. For example, it is possible that dogs presenting with more severe hepatic encephalopathy were more likely to be considered poor surgical candidates by some surgeons or, conversely, would have been considered less amenable to medical therapy because of residual clinical signs. It is also possible that in those dogs in which surgery was not selected because of financial reasons, poor compliance with medication due to cost may have influenced survival times or willingness to aggressively manage patients that required occasional hospitalization because of worsening clinical signs. Finally, because only dogs with clinical signs were included in this study,2 whether the long-term survival of asymptomatic patients likewise differs depending on the method of treatment is unknown.

Ultimately, despite the bias involved in patient selection, these conclusions are encouraging for recommending medical management in cases in which surgical intervention cannot be immediately—or ever—considered. Owners should be informed that survival beyond three years occurs in more than 50% of cases, but median survival (time until death of 50% of patients) or effect on true long-term survival is still unknown. A dog's quality of life during this period, meaning persistence of clinical signs due to hepatic encephalopathy, may still be worse than in surgically treated dogs and is ultimately unknown. The reasons why medical management is associated with shorter long-term survival were not investigated but are likely associated with previous authors' findings that although medical management can be equally effective at controlling clinical signs of hepatic encephalopathy and correcting some or all biochemical abnormalities, progressive hepatic fibrosis occurs in dogs that do not undergo surgical correction.1

Greenhalgh SN, Dunning MD, McKinley TJ, et al. Comparison of survival after surgical or medical treatment in dogs with a congenital portosystemic shunt. J Am Vet Med Assoc 2010;236(11):1215-1220.

The information in "Research Updates" was provided by Scott Owens, DVM, and Barrak Pressler, DVM, PhD, DACVIM, Department of Veterinary Clinical Sciences, School of Veterinary Medicine, Purdue University, West Lafayette, IN 47907.

REFERENCES

1. Faverzani S, Trombetta R, Grieco V, et al. Clinical, laboratory, ultrasonographic and histopathological findings in dogs affected by portosystemic shunts, following surgery or medical treatment. Vet Res Commun 2003;27 Suppl 1:755-758.

2. Greenhalgh SN, Jeffery ND. Author response to: Willard M. Requests clarification on study of congenital portosystemic shunts. J Am Vet Med Assoc 2010;237(6):624.

3. Watson PJ, Herrtage ME. Medical management of congenital portosystemic shunts in 27 dogs—a retrospective study. J Small Anim Pract 1998;39(2):62-68.