Can blood serum amyloid A concentrations in horses differentiate synovial sepsis from extrasynovial inflammation and determine response to treatment?

Abstract

BackgroundSerum amyloid A (SAA) concentrations in blood and synovial fluid of horses with synovial sepsis have diagnostic value. Studies suggest serial blood SAA measurements could act as a prognostic indicator. This study evaluated the use of serial blood SAA concentrations for monitoring of horses with synovial sepsis.MethodsA prospective clinical trial was performed of horses referred to a single hospital with synovial sepsis that survived (n=17), synovial sepsis that were euthanised (n=5), non-septic intrasynovial pathologies (n=14) or extensive extrasynovial lacerations (n=5). SAA concentrations were determined on admission and every 24 hours thereafter. The area under the concentration–time curve from 0 to 144 hours of each group was compared by Kruskal-Wallis and post hoc Dunn’s tests (P<0.05).ResultsSignificant difference in mean blood concentration of SAA was found between synovial sepsis that survived and non-septic pathologies in the first 48 hours, as well as between non-septic intrasynovial pathologies and non-responsive sepsis requiring euthanasia. No difference was found between extensive extrasynovial lacerations and any septic group.ConclusionsWhile serial blood SAA is useful for monitoring clinical response of intrasynovial septic pathologies, interpretation should consider other clinical findings since blood SAA is not a specific marker for synovial sepsis.

Use of serum amyloid A in equine medicine and surgery

“…This is particularly useful in cases awaiting culture results, where the choice of antibiotics is initially based on preliminary clinical evidence and the clinician's experience. Declining SAA concentration has been demonstrated to parallel successful treatment of synovial sepsis 93,113 and pneumonia in foals. 108 In horses undergoing exploratory laparotomy, SAA initially increases in response to the surgical trauma and then, in the absence of surgical site or other infections, declines toward normal within 4-6 96,114 and 11 days, 5 depending on the extent of the surgical trauma.…”

“…However, results of studies attempting to link early assessment of SAA to outcome are generally discouraging, as most equine studies have failed to demonstrate a reliable prognostic value of measuring SAA. 93,97,110,111 To evaluate the ability of SAA and haptoglobin to predict survival, Westerman et al (2015) 97 measured plasma SAA and haptoglobin concentrations at the time of admission in 53 horses (36 survivors and 17 nonsurvivors) with a variety of inflammatory conditions (peritonitis, colitis, trauma, renal insufficiency and cystitis, pneumonia, cellulitis, fever of unknown origin, and miscellaneous). The authors found that a single-point measurement of the two APPs was not significantly associated with survival outcomes and suggested that serial analysis during treatment might be a better prognostic tool.…”

“…In contrast to these findings, daily measurements of SAA in horses being treated for synovial sepsis were unable to predict outcome (survival/nonsurvival). 93 Using admission concentrations of SAA for predicting outcome in horses admitted with colic has been investigated in three studies. 8,111,112 A retrospective study investigated SAA concentration at admission in 718 horses with acute abdominal pain admitted to two centers.…”

“…Similar to other inflammatory markers, SAA will be produced in response to inflammation independent of etiology, so SAA cannot be used to make etiological diagnoses. Aseptic tissue injury and inflammation (accidental or iatrogenic, eg, vaccination or surgery) as well as infectious diseases will elicit an SAA response, 24,71,83,90–94 It has been suggested that viral disease is accompanied by lower serum SAA concentrations than the bacterial disease 94 . However, overlap between groups is substantial, and while SAA may give an indication of etiology, it cannot categorically distinguish viral infections from bacterial ones.…”

The synovial fluid proteome differentiates between septic and nonseptic articular pathologies

“…This situation can lead to erroneous interpretations and clinical decisions, representing an important welfare risk to the horse. More specific proteins such as the acute phase inflammatory protein serum amyloid A has been investigated as a potential biomarker of articular conditions in horses [7]; however, it is easily affected by the systemic condition of the patient, and therefore, can be unreliable for specific clinical diagnosis [8].…”