Biomarkers of non-infectious inflammatory CNS diseases in dogs - Where are we now? Part I: Meningoencephalitis of unknown origin

Meningoencephalitides of Unknown Origin (MUO) comprises a group of non-infectious inflammatory brain conditions, which frequently cause severe neurological disease and death in dogs. Although multiple diagnostic markers have been investigated, a conclusive diagnosis, at present, essentially relies on postmortem histopathology. However, different groups of biomarkers, e.g. acute phase proteins, antibodies, cytokines, and neuro-imaging markers may prove useful in the diagnostic investigation of dogs with MUO. It appears from the current literature that acute phase proteins such as C-reactive protein are often normal in MUO, but may be useful to rule out steroid responsive meningitis-arteritis as well as other systemic inflammatory conditions. In antibody research, anti-glial fibrillary acidic protein (GFAP) may play a role, but further research is needed to establish this as a consistent marker of particularly Pug dog encephalitis. The proposed diagnostic markers often lack specificity to distinguish between the subtypes of MUO, but an increased expression of interferon-γ (IFN-γ) in necrotizing meningoencephalitis (NME) and interleukin-17 (IL-17) in granulomatous meningoencephalitis (GME) in tissue biopsies may indicate their potential as specific markers of NME and GME, respectively, suggesting further investigations of these in serum and CSF. While neuro-imaging is already an important part of the diagnostic work-up in MUO, further promising results have been shown with Positron Emission Tomography (PET) as well as proton resonance spectroscopy (¹H MRS), which may be able to detect areas of necrosis and granulomas, respectively, with relatively high specificity. This review presents different groups of established and potential diagnostic markers of MUO assessing current results and future potential.

Anesthetic effects of isoflurane and propofol on cerebrospinal fluid biochemical markers in healthy dogs

BACKGROUND

The study of brain energy metabolism (BEM) markers in the cerebrospinal fluid (CSF) is a potential diagnostic and prognostic tool for many central nervous system (CNS) diseases. To date, in veterinary medicine, few studies are reporting physiologic ranges for some BEM markers. Recently, the influence of anesthetic drugs on BEM markers has been described in mice; subsequently, the study of CSF-BEM markers has gained increasing attention.

OBJECTIVES

The effects of anesthetic agents on BEM are poorly understood in dogs. The aim of this study was to evaluate the influence of propofol, isoflurane, and the duration of anesthesia on CSF-BEM markers in dogs.

METHODS

Nine dogs were anesthetized at two different periods, one month apart. In the first period, the dogs were intravenously anesthetized with propofol (PRO-group), and in the second period, the dogs received inhalant anesthesia with isoflurane (ISO-group). In both cases, CSF and blood were collected 15 minutes (T0) and 3 hours after induction (T3) and analyzed for lactate, pyruvate, glucose, creatine kinase, glutamate, and electrolyte concentrations.

RESULTS

CSF lactate (CSF-L) showed variation depending on the anesthetic agent and time, being significantly lower after 3 hours of anesthesia in the PRO-group and showing a trend to increase over time in the ISO-group. No changes were detected over time or between groups in CSF glutamate, glucose, or electrolytes.

CONCLUSIONS

The results of this study support that the anesthetic drug choice and length of the general anesthesia should be considered when CSF-L analyses are interpreted in dogs.

Comparison of concentrations of γ-aminobutyric acid and glutamate in cerebrospinal fluid of dogs with idiopathic epilepsy with and without seizure-related magnetic resonance imaging hyperintense areas in the limbic system

OBJECTIVE

To investigate differences in CSF concentrations of excitatory and inhibitory neurotransmitters in dogs with and without T2-weighted (T2W) MRI hyperintense areas in the limbic system.

SAMPLE

Archived CSF samples and stored brain MRI images of 5 healthy research dogs (group 1), 8 dogs with idiopathic epilepsy (IE) with no abnormal MRI findings (group 2), and 4 dogs with IE with hyperintense areas in the limbic system detected by means of T2W MRI (group 3).

PROCEDURES

Archived CSF samples and stored MRI images obtained from all dogs were evaluated. Dogs in groups 2 and 3 were matched on the basis of age and breed. High-performance liquid chromatography was used to evaluate glutamate and γ-aminobutyric acid (GABA) concentrations in CSF samples.

RESULTS

Glutamate concentrations were higher in CSF of both groups of dogs with IE than in healthy dogs. However, glutamate concentrations in CSF were not significantly higher in dogs with IE and with hyperintense areas than in dogs with IE but no abnormal MRI findings. Concentrations of GABA in CSF were higher in group 3 than in group 2 and in group 2 than in group 1.

CONCLUSIONS AND CLINICAL RELEVANCE

No significant difference was evident between glutamate concentrations in CSF of dogs with IE and with and without hyperintense areas detected by means of T2W MRI. However, glutamate concentrations typically were higher in CSF of dogs with IE and MRI hyperintense areas. Future studies with larger sample sizes should be conducted to confirm this finding and to determine the clinical importance of high glutamate concentrations in CSF of dogs with IE.