Fiona M. K. James

Clinical and MRI Findings in Three Dogs with Polycystic Meningiomas

One spayed female Labrador retriever and two castrated male golden retrievers were evaluated for chronic (i.e., ranging from 3 wk to 24 wk) neurologic signs localizable to the prosencephalon. Signs included seizures, circling, and behavior changes. MRI demonstrated extra-axial, contrast-enhancing, multiloculated, fluid-filled, cyst-like lesions with a mass effect, causing compression and displacement of brain parenchyma. Differential diagnoses included cystic neoplasm, abscess or other infectious cyst (e.g., alveolar hydatid cyst), or fluid-filled anomaly (e.g., arachnoid cyst). The cyst-like lesions were attached to the rostral falx cerebri in all cases. In addition, case 2 had a second polycystic mass at the caudal diencephalon. Surgical biopsy (case 3 with a single, rostral tumor via transfrontal craniectomy) and postmortem histology (in cases 1 and 2) confirmed polycystic meningiomas. Tumor types were transitional (cases 1 and 3) and fibrous (case 2), with positive immunohistochemical staining for vimentin. Case 3 was also positive for E-cadherin, s100, and CD34. In all cases, staining was predominantly negative for glial fibrillary acid protein and pancytokeratins, supporting a diagnosis of meningioma. This report describes the first cases of polycystic meningiomas in dogs. Polycystic meningiomas are a rare, but important, addition to the differential diagnoses for intracranial cyst-like lesions, significantly affecting planning for surgical resection and other therapeutic interventions.

Investigation of the use of three electroencephalographic electrodes for long-term electroencephalographic recording in awake and sedated dogs

OBJECTIVE To compare electroencephalography (EEG) artifact associated with use of the subdermal wire electrode (SWE), gold cup electrode (GCE), and subdermal needle electrode (SNE) over an 8-hour period in sedated and awake dogs. ANIMALS 6 healthy dogs. PROCEDURES 8 EEG channels were recorded during 20-minute video-EEG recording sessions (intermittently at 0.5, 2, 4, 6, and 8 hours) with and without chlorpromazine sedation. Nonphysiologic artifacts were identified. Duration of artifact was summed for each channel. Number of unaffected channels (NUC) was determined. RESULTS NUC was significantly affected by electrode type and sedation over time; median for SWE (2.80 channels; 95% confidence interval [CI], 0.84 to 5.70 channels) was significantly different from medians for GCE (7.87 channels; 95% CI, 7.44 to 7.94 channels) and SNE (7.60 channels; 95% CI, 6.61 to 7.89 channels). After 4 hours, NUC decreased in awake dogs, regardless of electrode type. In awake dogs, duration of artifact differed significantly between SWE and GCE or SNE; medians at 8 hours were 61.55 seconds (95% CI, 21.81 to 173.65 seconds), 1.33 seconds (95% CI, 0.47 to 3.75 seconds), and 21.01 seconds (95% CI, 6.85 to 64.42 seconds), respectively. CONCLUSIONS AND CLINICAL RELEVANCE The SWE had a significant duration of artifact during recording periods > 2 hours, compared with results for the GCE and SNE, in awake dogs. The GCE, SNE, and sedation resulted in significantly more channels unaffected by artifact. For longer recordings, caution should be exercised in selecting EEG electrodes and sedation state, although differences among electrodes may not be clinically relevant.

Diagnostic Utility of Wireless Video-Electroencephalography in Unsedated Dogs

Background Poor agreement between observers on whether an unusual event is a seizure drives the need for a specific diagnostic tool provided by video‐electroencephalography (video‐EEG) in human pediatric epileptology. Objective That successful classification of events would be positively associated with increasing EEG recording length and higher event frequency reported before video‐EEG evaluation; that a novel wireless video‐EEG technique would clarify whether unusual behavioral events were seizures in unsedated dogs. Animals Eighty‐one client‐owned dogs of various breeds undergoing investigation of unusual behavioral events at 4 institutions. Methods Retrospective case series: evaluation of wireless video‐EEG recordings in unsedated dogs performed at 4 institutions. Results Electroencephalography achieved/excluded diagnosis of epilepsy in 58 dogs (72%); 25 dogs confirmed with epileptic seizures based on ictal/interictal epileptiform discharges, and 33 dogs with no EEG abnormalities associated with their target events. As reported frequency of the target events decreased (annually, monthly, weekly, daily, hourly, minutes, seconds), EEG was less likely to achieve diagnosis (P < 0.001). Every increase in event frequency increased the odds of achieving diagnosis by 2.315 (95% confidence interval: 1.36–4.34). EEG recording length (mean = 3.69 hours, range: 0.17–22.5) was not associated (P = 0.2) with the likelihood of achieving a diagnosis. Conclusions and Clinical Importance Wireless video‐EEG in unsedated dogs had a high success for diagnosis of unusual behavioral events. This technique offered a reliable clinical tool to investigate the epileptic origin of behavioral events in dogs.

Generalized myoclonic epilepsy with photosensitivity in juvenile dogs caused by a defective DIRAS family GTPase 1

Significance Comprehensive clinical, neurological, and genetic examinations characterized a generalized myoclonic epilepsy syndrome with photosensitivity in young Rhodesian Ridgeback dogs. The average age of onset of seizures was 6 mo. Genetic analyses revealed a defective DIRAS family GTPase 1 (DIRAS1) gene and protein. DIRAS1 is widely expressed in the brain and has been suggested to regulate acetylcholine release and play a role in neurodevelopment. This study reveals a candidate gene for human myoclonic epilepsies, and a translational model to further elucidate the role of DIRAS1 in neurotransmission and neurodevelopment, and its modulation as a therapeutic option in common epilepsy. The clinical and electroencephalographic features of a canine generalized myoclonic epilepsy with photosensitivity and onset in young Rhodesian Ridgeback dogs (6 wk to 18 mo) are described. A fully penetrant recessive 4-bp deletion was identified in the DIRAS family GTPase 1 (DIRAS1) gene with an altered expression pattern of DIRAS1 protein in the affected brain. This neuronal DIRAS1 gene with a proposed role in cholinergic transmission provides not only a candidate for human myoclonic epilepsy but also insights into the disease etiology, while establishing a spontaneous model for future intervention studies and functional characterization.

A CHRNE frameshift mutation causes congenital myasthenic syndrome in young Jack Russell Terriers

Congenital myasthenic syndromes (CMSs) are a group of rare genetic disorders of the neuromuscular junction resulting in structural or functional causes of fatigable weakness that usually begins early in life. Mutations in pre-synaptic, synaptic and post-synaptic proteins have been demonstrated in human cases, with more than half involving aberrations in nicotinic acetylcholine receptor (AChR) subunits. CMS was first recognized in dogs in 1974 as an autosomal recessive trait in Jack Russell Terriers (JRTs). A deficiency of junctional AChRs was demonstrated. Here we characterize a CMS in 2 contemporary cases of JRT littermates with classic clinical and electromyographic findings, and immunochemical confirmation of an approximately 90% reduction in AChR protein content. Loci encoding the 5 AChR subunits were evaluated using microsatellite markers, and CHRNB1 and CHRNE were identified as candidate genes. Sequences of the splice sites and exons of both genes revealed a single base insertion in exon 7 of CHRNE that predicts a frameshift mutation and a premature stop codon. We further demonstrated this pathogenic mutation in CHRNE in archival tissues from unrelated JRTs studied 34 years ago.

The effect of topical lidocaine on muscle artefacts in awake canine electroencephalogram recordings

Muscle artefacts in electroencephalogram recording data interfere with diagnostic accuracy. Lidocaine may reduce these artefacts. The objective of this study was to determine the effect of topical lidocaine on muscle artefacts in unanesthetized canine electroencephalogram (EEG) recording data. Topical 4% lidocaine was applied to each electrode site for six treated dogs prior to subdermal wire electrode placement and compared against historical untreated controls. Twenty-minute recordings began 30 min after lidocaine application. Three epochs (early, middle, and end) were sampled from each recording and scored for muscle artefact incidence and severity by two blinded reviewers. No significant treatment effects on incidence and severity were found. Application of topical lidocaine does not appear to reduce the occurrence of muscle artefacts in canine EEG recordings.

Computed Tomographic Analysis of Ventral Atlantoaxial Optimal Safe Implantation Corridors in 27 Dogs

Objectives Ventral atlantoaxial stabilization techniques are challenging surgical procedures in dogs. Available surgical guidelines are based upon subjective anatomical landmarks, and limited radiographic and computed tomographic data. The aims of this study were (1) to provide detailed anatomical descriptions of atlantoaxial optimal safe implantation corridors to generate objective recommendations for optimal implant placements and (2) to compare anatomical data obtained in non-affected Toy breed dogs, affected Toy breed dogs suffering from atlantoaxial instability and non-affected Beagle dogs. Methods Anatomical data were collected from a prospectively recruited population of 27 dogs using a previously validated method of optimal safe implantation corridor analysis using computed tomographic images. Results Optimal implant positions and three-dimensional numerical data were generated successfully in all cases. Anatomical landmarks could be used to generate objective definitions of optimal insertion points which were applicable across all three groups. Overall the geometrical distribution of all implant sites was similar in all three groups with a few exceptions. Clinical Significance This study provides extensive anatomical data available to facilitate surgical planning of implant placement for atlantoaxial stabilization. Our data suggest that non-affected Toy breed dogs and non-affected Beagle dogs constitute reasonable research models to study atlantoaxial stabilization constructs.

Computed Tomography and Biomechanical Comparison between Trans-Articular Screw Fixation and 2 Polymethylmethacrylate Cemented Constructs for Ventral Atlantoaxial Stabilization

OBJECTIVES  Canine ventral atlantoaxial stabilization methods have been constantly evolving over the past few decades. Yet, proper experimental data comparing the feasibility and biomechanical properties of currently available surgical options are lacking. The aims of this study were (1) to describe and compare the safety profiles and biomechanical properties of three ventral atlantoaxial stabilization methods; and (2) to test whether recently reported optimal implant definitions constitute reasonable guidelines. METHODS  Three types of atlantoaxial stabilization including trans-articular screw fixation (TSF) and two cemented constructs (MI5 and MI6) were performed in 21 Beagle cadavers. Post-surgical computed tomography (CT) images of the constructs and biomechanical data were then generated and statistically analysed. RESULTS  The CT data revealed that TSF achieved significantly better apposition than cemented constructs. Out of 91 screws positioned, 4.4% were graded as dangerous and 86.8% as optimal. Optimal positioning was most challenging to obtain for mono-cortical screws. Analysis of biomechanical data suggested that all three techniques could likely achieve similar rates of atlantoaxial fusion when submitted to physiological loads but also that cemented constructs were less prone to failure compared with TSF. CLINICAL SIGNIFICANCE  This study provides evidence that all three techniques are technically feasible and biomechanically viable but also that the evaluated surgical guidelines could be improved.

Absence Seizures as a Feature of Juvenile Myoclonic Epilepsy in Rhodesian Ridgeback Dogs

Myoclonic epilepsy in Rhodesian Ridgeback (RR) dogs is characterized by myoclonic seizures occurring mainly during relaxation periods, a juvenile age of onset and generalized tonic‐clonic seizures in one‐third of patients. An 8‐month‐old female intact RR was presented for myoclonic seizures and staring episodes that both started at 10 weeks of age. Testing for the DIRAS1 variant indicated a homozygous mutant genotype. Unsedated wireless video‐electroencephalography (EEG) identified frequent, bilaterally synchronous, generalized 4 Hz spike‐and‐wave complexes (SWC) during the staring episodes in addition to the characteristic myoclonic seizures with generalized 4–5 Hz SWC or 4–5 Hz slowing. Photic stimulation did not evoke a photoparoxysmal response. Repeat video‐EEG 2 months after initiation of levetiracetam treatment disclosed a >95% decrease in frequency of myoclonic seizures, and absence seizures were no longer evident. Absence seizures represent another seizure type in juvenile myoclonic epilepsy (JME) in RR dogs, which reinforces its parallels to JME in humans.

Anophthalmia in a Wild Eastern Gray Squirrel (Sciurus carolinensis)

Abstract We describe bilateral true anophthalmia in a juvenile female eastern gray squirrel (Sciurus carolinensis) with histologic confirmation that orbital contents lacked ocular tissues. Additionally, the optic chiasm of the brain was absent and axon density in the optic tract adjacent to the lateral geniculate nucleus was reduced.