New insights into neuropathology and pathogenesis of autoimmune glial fibrillary acidic protein meningoencephalomyelitis

Anti-glial fibrillary acidic protein (GFAP) meningoencephalomyelitis (autoimmune GFAP astrocytopathy) is a new autoimmune central nervous system (CNS) disease diagnosable by the presence of anti-GFAP autoantibodies in the cerebrospinal fluid and presents as meningoencephalomyelitis in the majority of patients. Only few neuropathological reports are available and little is known about the pathogenic mechanisms. We performed a histopathological study of two autopsies and nine CNS biopsies of patients with anti-GFAP autoantibodies and found predominantly a lymphocytic and in one autopsy case a granulomatous inflammatory phenotype. Inflammatory infiltrates were composed of B and T cells, including tissue-resident memory T cells. Although obvious astrocytic damage was absent in the GFAP-staining, we found cytotoxic T cell-mediated reactions reflected by the presence of CD8+/perforin+/granzyme A/B+ cells, polarized towards astrocytes. MHC-class-I was upregulated in reactive astrocytes of all biopsies and two autopsies but not in healthy controls. Importantly, we observed a prominent immunoreactivity of astrocytes with the complement factor C4d. Finally, we provided insight into an early phase of GFAP autoimmunity in an autopsy of a pug dog encephalitis that was characterized by marked meningoencephalitis with selective astrocytic damage with loss of GFAP and AQP4 in the lesions.Our histopathological findings indicate that a cytotoxic T cell-mediated immune reaction is present in GFAP autoimmunity. Complement C4d deposition on astrocytes could either represent the cause or consequence of astrocytic reactivity. Selective astrocytic damage is prominent in the early phase of GFAP autoimmunity in a canine autopsy case, but mild or absent in subacute and chronic stages in human disease, probably due to the high regeneration potential of astrocytes. The lymphocytic and granulomatous phenotypes might reflect different stages of lesion development or patient-specific modifications of the immune response. Future studies will be necessary to investigate possible implications of pathological subtypes for clinical disease course and therapeutic strategies.

Investigation of side effects to treatment and cause of death in 63 Scandinavian dogs suffering from meningoencephalitis of unknown origin: a retrospective study

BACKGROUND

Meningoencephalitis of unknown origin is a common cause of severe neurological disease in dogs. The term covers a heterogeneous group of noninfectious inflammatory diseases, with immune dysregulation widely accepted as the underlying disease mechanism. Current treatment consists of immunosuppression, with corticosteroids being the mainstay of virtually all treatment regimens. However, side effects of corticosteroids can be severe, and might be the cause of death in some patients. This retrospective, multi-centric study aimed at describing a population of Scandinavian dogs with meningoencephalitis of unknown origin in regards to reported side effects and cause of death, and to highlight possible differences in survival, when comparing corticosteroid monotherapy with other treatment regimens.

RESULTS

Within the 5-year study period, 63 dogs were included. Of these, 35 (49.3%) died or were euthanized during the study period. Median survival time from time of diagnosis based on Kaplan-Meier curves for the overall population was 714 days (equivalent to around 25 months, range 0-1678 days). There was no statistically significant difference (P = 0.31) in survival between dogs treated with corticosteroid monotherapy (n = 26, median survival time 716 days, equivalent to around 25 months, range 5-911 days), dogs receiving a combination of corticosteroids and ciclosporin (n = 15, median survival time 916 days, equivalent to around 31 months, range 35-1678 days), and dogs receiving corticosteroids combined with either cytosine arabinoside, leflunomide, or a combination of 2 or more add-on drugs (n = 13, median survival time 1186 days, equivalent to around 40 months, range 121-1640 days). Side effects were registered for 47/63 dogs. Polyphagia (n = 37/47), polyuria/polydipsia (n = 37/47), diarrhea (n = 29/47) and lethargy (n = 28/47) were most frequently reported. The most common cause for euthanasia was relapse (n = 15/35, 42.9%), followed by insufficient or lack of treatment response (n = 9, 25.7%). Side effects were the direct cause of euthanasia in 2/35 dogs (5.7%).

CONCLUSIONS

A large proportion of dogs in the overall population were euthanized due to relapse, emphasizing a need for treatment regimens aimed at specifically preventing relapse for an improved long-term survival. Side effects in dogs receiving corticosteroid monotherapy were rarely a direct cause of death, but were reported for all dogs. No statistically significant difference in survival was found when corticosteroid monotherapy was compared to other treatment regimens.

Magnetic Resonance Imaging Characteristics of Autoimmune Glial Fibrillary Acidic Protein (GFAP) Astrocytopathy: A Pediatric Series in Southwest China

Objective

To investigate and summarize the magnetic resonance imaging (MRI) manifestations of autoimmune glial fibrillary acidic protein (GFAP) astrocytopathy in children.

Methods

We retrospectively analyzed data from 17 pediatric patients with autoimmune GFAP astrocytopathy confirmed by the detection of GFAP autoantibodies in cerebrospinal fluid in our single-center. Furthermore, we reviewed current literature and summarized previous findings on the MRI characteristics of this disease in children.

Results

In these 17 patients, the clinical manifestations and results of CSF analysis were suggestive of autoimmune disorder, with a good improvement. The lesions on MRI were most commonly located in the bilateral basal ganglia (70.6%), thalamus (64.7%), cerebral white matter (29.4%). 93.3% of the cerebral lesions were relatively scattered and small, 80% of the spinal lesions presented as longitudinally extensive ones. Both periventricular radial linear (PVRL) (53.8%) and punctate or linear enhancement in basal ganglia and thalamus (53.8%) were commonly observed, followed by the leptomeningeal enhancement (46.2% in the brain and 62.5% in the spinal cord). We then included 55 pediatric patients with MRI data from current literature in our analysis (n = 72, 44 males). Our results revealed similar MRI findings but the enhancement pattern between our series and previously published cases, that is, leptomeningeal enhancement in the brain 46.2% vs 31.4%, in spinal cord 62.5% vs 18.4%, and PVRL enhancement 53.8% vs 11.2%. There were no detailed reports on punctate or linear enhancement.

Conclusion

The MRI characteristics of autoimmune GFAP astrocytopathy in children could be suggestive. Scattered and small lesions (especially punctate or linear) in the bilateral thalamus, basal ganglia, and white matter, as well as longitudinally extensive spinal cord lesions (if present), with punctate, PVRL and leptomeningeal enhancement might be a distinct indication for the early diagnosis of this disorder.

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.

Expression of platelet-derived growth factor receptor-α/ß, vascular endothelial growth factor receptor-2, c-Abl, and c-Kit in canine granulomatous meningoencephalitis and necrotizing encephalitis

Background

Given the active research on targeted therapy using tyrosine kinase (TK) inhibitors (TKIs) in the field of oncology, further studies have recently been conducted to evaluate their use in autoimmune disorders. Based on immunological investigations, previous studies have suggested that granulomatous meningoencephalomyelitis (GME) and necrotizing encephalomyelitis (NE) are similar to multiple sclerosis (MS), which is a human autoimmune demyelinating central nervous system disease.

Objectives

Considering this perspective, we hypothesized that canine GME and NE have significant expression of one or more TKs, which are associated with human MS pathogenesis.

Methods

To determine the possible use of conventional multi‐targeted TKIs as a treatment for canine GME and NE, we characterized the immunohistochemical expression of platelet‐derived growth factor receptor (PDGFR)‐α, PDGFR‐ß, vascular endothelial growth factor receptor (VEGFR)‐2, c‐Abl and c‐Kit in GME and NE samples.

Results

Histological samples from four dogs with GME and three with NE were retrieved. All samples stained positive for PDGFR‐ß (7/7 [100%]). PDGFR‐α and c‐Kit were expressed in 3/7 (42.8%) samples each. c‐Abl was identified in 2/7 (28.5%) samples; no sample showed VEGFR‐2 (0%) expression. Co‐expression of TKs was identified in 6/7 (85.7%) dogs.

Conclusions

All samples were positive for at least one or more of PDGFR‐α, PDGFR‐ß, c‐Kit and c‐Abl, which are known as the target TKs of conventional multi‐targeted TKIs. Their presence does suggest that these TKs may play a role in the pathogenesis of GME and NE. Therefore, multi‐targeted TKIs may provide benefits in the treatment of canine GME and NE by suppressing the activity of these TKs.

Autoimmune Glial Fibrillary Acidic Protein Astrocytopathy: A Review of the Literature

Autoimmune glial fibrillary acidic protein (GFAP) astrocytopathy is an autoimmune disease of the nervous system first defined in 2016. GFAP autoantibody, especially IgG that binds to GFAPα, has been reported in the cerebrospinal fluid (CSF) and serum of patients with GFAP astrocytopathy. The positive predictive value of GFAP antibody in the CSF is higher than in the serum. Tissue-based assay (TBA) and cell-based assay (CBA) are both recommended methods for the detection of GFAP antibody. GFAP astrocytopathy is accompanied by neoplasms, but the relationship between virus infection and GFAP astrocytopathy is unclear. GFAP antibody itself does not induce pathological changes; it is only a biomarker for the process of immune inflammation. The pathology of GFAP astrocytopathy in humans is heterogeneous. GFAP astrocytopathy is commonly diagnosed in individuals over 40 years old and most patients have an acute or subacute onset. Clinical manifestations include fever, headache, encephalopathy, involuntary movement, myelitis, and abnormal vision. Lesions involve the subcortical white matter, basal ganglia, hypothalamus, brainstem, cerebellum, and spinal cord. The characteristic MRI feature is brain linear perivascular radial gadolinium enhancement in the white matter perpendicular to the ventricle. Currently, there are no uniform diagnostic criteria or consensus for GFAP astrocytopathy and coexisting neural autoantibodies detected in the same patient make the diagnosis difficult. A standard treatment regimen is yet to be developed. Most GFAP astrocytopathy patients respond well to steroid therapy although some patients are prone to relapse or even die.

Biomarkers of injury to neural tissue in veterinary medicine

There are numerous biomarkers of central and peripheral nervous system damage described in human and veterinary medicine. Many of these are already used as tools in the diagnosis of human neurological disorders, and many are investigated in regard to their use in small and large animal veterinary medicine. The following review presents the current knowledge about the application of cell-type (glial fibrillary acidic protein, neurofilament subunit NF-H, myelin basic protein) and central nervous system specific proteins (S100B, neuron specific enolase, tau protein, alpha II spectrin, ubiquitin carboxy-terminal hydrolase L1, creatine kinase BB) present in the cerebrospinal fluid and/or serum of animals in the diagnosis of central or peripheral nervous system damage in veterinary medicine.

Unsuccessful cyclosporine plus prednisolone therapy for autoimmune meningoencephalitis in three dogs

A 4-year-old female Maltese (case 1), a 9-year-old castrated male shih tzu (case 2) and 2-year-old female Pomeranian (case 3) presented with neurological signs, such as head tilt, ataxia, circling and paresis. The three cases were tentatively diagnosed as having meningoencephalitis of unknown etiology based on computed tomography scan and cerebrospinal fluid analysis. All patients were managed with cyclosporine plus prednisolone therapy. The survival times of the three patients were 170, 70 and 21 days, respectively. After the cases died, we performed necropsy and histopathological examination for definitive diagnosis. Based on the necropsy, histopathological and immunohistochemical examinations, cases 1, 2 and 3 were definitely diagnosed as having necrotizing meningoencephalitis, necrotizing leukoencephalitis and granulomatous meningoencephalitis, respectively. This case report demonstrated the clinical findings, brain CT characteristics and histopathological and immunohistochemical features of NME, NLE and GME in dogs and discussed the reason for the relatively short survival times under cyclosporine plus prednisolone therapy.

Necrotizing meningoencephalitis of Pug dogs associates with dog leukocyte antigen class II and resembles acute variant forms of multiple sclerosis

Necrotizing meningoencephalitis (NME) is a disorder of Pug Dogs that appears to have an immune etiology and high heritability based on population studies. The present study was undertaken to identify a genetic basis for the disease. A genome-wide association scan with single tandem repeat (STR) markers showed a single strong association near the dog leukocyte antigen (DLA) complex on CFA12. Fine resolution mapping with 27 STR markers on CFA12 further narrowed association to the region containing DLA-DRB1, -DQA1 and, -DQB1 genes. Sequencing confirmed that affected dogs were more likely to be homozygous for specific alleles at each locus and that these alleles were linked, forming a single high risk haplotype. The strong DLA class II association of NME in Pug Dogs resembles that of human multiple sclerosis (MS). Like MS, NME appears to have an autoimmune basis, involves genetic and nongenetic factors, has a relatively low incidence, is more frequent in females than males, and is associated with a vascularly orientated nonsuppurative inflammation. However, NME of Pug Dogs is more aggressive in disease course than classical human MS, appears to be relatively earlier in onset, and involves necrosis rather than demyelination as the central pathobiologic feature. Thus, Pug Dog encephalitis (PDE) shares clinical features with the less common acute variant forms of MS. Accordingly, NME of Pug Dogs may represent a naturally occurring canine model of certain idiopathic inflammatory disorders of the human central nervous system.