Imagine this clinical scenario: a six-month-old male Yorkshire Terrier puppy has preanaesthetic bloodwork and subsequent bile acid stimulation test results that are consistent with an extrahepatic portosystemic shunt (EHPSS). Assuming her dog has an EHPSS, the owner would like to know how surgical attenuation compares with non-surgical medical management in terms of prognosis and outcome of neurological dysfunction.
You decide to explore whether there is evidence that surgical or medical management of EHPSS carries a better prognosis for resolving and reducing neurological dysfunction.
Ten retrospective studies were critically reviewed. Six were cohort studies, with sample sizes ranging from 44 to 940 dogs. Four were descriptive case series studies, with sample sizes ranging from 17 to 56 dogs. Studies that directly compared the impact of surgical and medical management on portosystemic shunts did not differentiate between intrahepatic and extrahepatic shunts and were therefore excluded.
Studies that directly compared the impact of surgical and medical management on portosystemic shunts did not differentiate between intrahepatic and extrahepatic shunts
Of the studies that did permit a review of the efficacy of treatment on EHPSS, two studies investigated medical management, and eight studies investigated surgical management. One of these surgical studies also reported outcomes on a period (median: 23 days; range: 0 to 730 days) of medical management immediately before surgery. Another of these surgical studies also reported that patients received a variable period of medical management but did not report on any associated outcomes. None of the studies compared the efficacy of medical versus surgical treatment for the management of EHPSS in decreasing neurological signs.
It should be noted that retrospective studies can have a higher level of bias than prospective studies. Further, both cohort studies and descriptive case studies series tend to have lower levels of evidence, though the former are considered more robust than the latter.
Ultimately there was very limited evidence on the efficacy of solely medical management for EHPSS in dogs
There were several specific limitations to the evidence. Most of the studies did not evaluate the persistence, frequency and severity of neurological dysfunction following either surgery or medical management as their primary problem. Additionally, several studies did not make a distinction between intrahepatic and extrahepatic shunts for several key variables, making interpretation of the findings difficult or impossible. Others had a small sample size (particularly when adjusted for EHPSS cases only), relied on owner recollection and/or had follow-up limitations, including loss of data and short duration of follow-up. Further, two studies were unclear as to either the medical interventions employed or the outcome of these interventions. Therefore, ultimately there was very limited evidence on the efficacy of solely medical management for EHPSS in dogs.
All surgical intervention-based studies reported that most dogs did not show neurological signs in the immediate post-operative period.
Fryer et al. (2011) found the lowest incidence of short-term post-operative neurological signs at 3 percent (4/126 dogs), while Wallace et al. (2018) found the highest incidence of short-term post-operative neurological signs at 29 percent (4/14 dogs). Worley and Holt (2008) found 71 percent (12/17 dogs) displayed preoperative neurological signs in their study. This decreased to 24 percent (4/17 dogs) after surgical attenuation and included one dog euthanised after it developed intractable seizures. All affected dogs displayed neurological signs preoperatively.
Tisdall et al. (2000) found that the overall proportion of dogs with neurological signs decreased from 79 percent (70/89 dogs) preoperatively to 12 percent (11/89 dogs) post-operatively with surgical attenuation. In the same study, the majority of dogs with post-operative neurological signs had also displayed neurological signs before surgery.
The majority of dogs with post-operative neurological signs had also displayed neurological signs before surgery
Two studies evaluating the long-term efficacy of surgical attenuation in decreasing neurological signs associated with EHPSS were reported on. While Wallace et al. (2018) and Harvey and Erb (1998) found owners reported no neurological signs had developed between 6 and 72 months and between 1 and 10 years, respectively, there were several limitations to these long-term evaluations.
In terms of evidence regarding the medical management of EHPSS, Watson and Herrtage (1998) found that some owners (43 percent, 3/7 dogs) reported a decrease in neurological signs after the initiation of medical management, as well as a reported increase in quality of life.
Favier et al. (2020), Watson and Herrtage (1998) and Strickland et al. (2018) found that the owners reported a decrease in neurological signs and an increase in quality of life after the initiation of medical management. However, these studies had relatively small sample sizes. Further, Watson and Herrtage (1998) found that only 33 percent (3/9) of the dogs were reported still alive three years after the end of the study.
Owners reported an overall decrease in the neurological signs associated with neurological dysfunction and an increase in quality of life after the initiation of either medical management or surgical management.
It is challenging to make a direct comparison between medical and surgical management given the limitations of the literature
It is challenging to make a direct comparison between medical and surgical management given the limitations of the literature, and there is a need for comparative studies to be undertaken.
The application of evidence in practice should take into account multiple factors, including but not limited to:
- individual clinical expertise
- patient’s circumstances and owner’s values
- country, location or clinic where you work
- the individual case in front of you
- the availability of therapies and resources
Knowledge Summaries are a resource to help reinforce or inform decision making. They do not override the responsibility or judgement of the practitioner to do what is best for the animal in their care.
A note from the Editor of Veterinary Evidence
This Knowledge Summary highlights some of the challenges for practitioners when evidence that directly compares the two (or more) interventions of interest is not available.
Readers considering writing a Knowledge Summary for Veterinary Evidence should note that our policy has changed since this submission and we now require PICOs that do not identify papers directly comparing the modalities or interventions of interest to be written up as “zero-evidence” Knowledge Summaries. Case studies, case series and other supporting studies that indirectly can be used to address the PICO can be utilised to support interpretations and contextualise discussions.
Typically, variation in the study design, patient demographics, reporting of clinical/experimental detail, outcome measures and time periods used make it challenging to compare management approaches or draw meaningful clinical conclusions. Here, there is an identified research gap for studies that directly compare short- and long-term efficacy of medical and surgical management of EHPSS.