Humoral Immune Responses in the Horse after Intrathecal Challenge with Ovalbumin

Cerebrospinal fluid Lyme multiplex assay results are not diagnostic in horses with neuroborreliosis

BACKGROUND

The accuracy of the Lyme multiplex assay for the diagnosis of neuroborreliosis in horses is unknown.

HYPOTHESIS/OBJECTIVES

To describe Lyme multiplex results in horses with a postmortem diagnosis of neuroborreliosis. The hypothesis was that paired serum and cerebrospinal fluid (CSF) results and a CSF : serum ratio would allow differentiation of horses with neuroborreliosis from those with other neurologic diseases.

ANIMALS

Ninety horses that had neurologic examinations, serum and CSF Lyme multiplex analyses, and postmortem examination of the nervous system performed.

METHODS

Retrospective study. Data collected included signalment, ante- and postmortem diagnoses, and serum and CSF Lyme multiplex results. The CSF : serum ratio was calculated by dividing CSF median fluorescent intensity (MFI) by serum MFI for each result.

RESULTS

Ten horses had a final diagnosis of neuroborreliosis, 70 were diagnosed with other neurologic diseases, and 10 had no neurologic disease. Not all horses with neuroborreliosis had positive results: 4/10 had at least 1 positive serum result, 5/10 had at least 1 positive CSF result, and 3/10 had at least 1 CSF result 4-fold higher than the corresponding serum result. Results were similar for the 70 horses with other neurologic diseases: 53% had at least 1 positive serum result, 50% had at least 1 positive CSF result, and 16% had at least 1 CSF result 4-fold higher than the corresponding serum result.

CONCLUSIONS AND CLINICAL IMPORTANCE

Positive Lyme multiplex results were common in horses with neurologic diseases and did not adequately differentiate horses with neuroborreliosis from horses with other disorders.

Use of albumin quotient and IgG index to differentiate blood- vs brain-derived proteins in the cerebrospinal fluid of cats with feline infectious peritonitis

Background: Inflammation of the central nervous system (CNS) is a frequent condition in cats but etiology often remains unsolved. Routine cerebrospinal fluid (CSF) analysis can be extended through the calculation of the albumin quotient (Q_alb), a marker of the integrity of the blood–brain barrier (BBB), and IgG index, an estimate of intrathecal IgG synthesis.

Objectives: The purpose of this study was to validate nephelometric methods for CSF protein analysis, and to use the Q_alb and IgG index to discriminate blood‐ and brain‐derived immunoglobulin fractions in cats with feline infectious peritonitis (FIP).

Methods: Cats presented to our clinic between 2001 and 2005 were included in the study based on clinical and laboratory data and histopathologic findings at necropsy. Cats were grouped as having nonneurologic disease (controls; n=37), brain tumors (n=8), FIP involving the CNS (n=12), and extraneural FIP (n=12). CSF‐total protein (TP) was measured and albumin and IgG concentrations were measured in paired CSF/serum samples; Q_alb and IgG index were calculated. Intraassay and interassay precision of the nephelometric assays were determined using pooled samples.

Results: Coefficients of variation for the nephelometric assays ranged from 2.7% to 7.2%. In control cats, CSF‐TP concentration ranged from 0.06 to 0.36 g/L, Q_alb ranged from 0.6 to 5.7 × 10⁻³, and IgG index ranged from 0.3 to 0.6. Q_alb and IgG index were significantly higher in cats with brain tumors and cats with CNS‐FIP compared with other groups. Compared with control cats, pleocytosis was evident in 8 of 12 (67%) cats and CSF‐TP was increased in 3 of 12 (25%) cats with CNS‐FIP.

Conclusion: Nephelometry is a reliable method for measurement of CSF protein, albumin, and IgG in cats. The Q_alb and IgG index did not identify a CSF protein pattern specific for BBB dysfunction or intrathecal IgG synthesis in cats with CNS‐FIP.