Qualitative and Quantitative Characteristics of the Electroencephalogram in Normal Horses during Administration of Inhaled Anesthesia

BACKGROUND

The effects of anesthesia on the equine electroencephalogram (EEG) after administration of various drugs for sedation, induction, and maintenance are known, but not that the effect of inhaled anesthetics alone for EEG recording.

OBJECTIVE

To determine the effects of isoflurane and halothane, administered as single agents at multiple levels, on the EEG and quantitative EEG (qEEG) of normal horses.

ANIMALS

Six healthy horses.

METHODS

Prospective study. Digital EEG with video and quantitative EEG (qEEG) were recorded after the administration of one of the 2 anesthetics, isoflurane or halothane, at 3 alveolar doses (1.2, 1.4 and 1.6 MAC). Segments of EEG during controlled ventilation (CV), spontaneous ventilation (SV), and with peroneal nerve stimulation (ST) at each MAC multiple for each anesthetic were selected, analyzed, and compared. Multiple non-EEG measurements were also recorded.

RESULTS

Specific raw EEG findings were indicative of changes in the depth of anesthesia. However, there was considerable variability in EEG between horses at identical MAC multiples/conditions and within individual horses over segments of a given epoch. Statistical significance for qEEG variables differed between anesthetics with bispectral index (BIS) CV MAC and 95% spectral edge frequency (SEF95) SV MAC differences in isoflurane only and median frequency (MED) differences in SV MAC with halothane only.

CONCLUSIONS AND CLINICAL IMPORTANCE

Unprocessed EEG features (background and transients) appear to be beneficial for monitoring the depth of a particular anesthetic, but offer little advantage over the use of changes in mean arterial pressure for this purpose.

Electroencephalogram of Healthy Horses During Inhaled Anesthesia

Background

Previous study of the diagnostic validity of electroencephalography (EEG) to detect abnormalities in equine cerebral cortical function relied on the administration of various drugs for sedation, induction, and maintenance of general anesthesia but used identical criteria to interpret recordings.

Objectives

To determine the effects of 2 inhalation anesthetics on the EEG of healthy horses.

Animals

Six healthy horses.

Methods

Prospective study. After the sole administration of one of either isoflurane or halothane at 1.2, 1.4, and 1.6 times the minimum alveolar concentration, EEG was recorded during controlled ventilation, spontaneous ventilation, and nerve stimulation.

Results

Burst suppression was observed with isoflurane, along with EEG events that resembled epileptiform discharges. Halothane results were variable between horses, with epileptiform‐like discharges and bursts of theta, alpha, and beta recorded intermittently. One horse died and 2 were euthanized as the result of anesthesia‐related complications.

Conclusions and Clinical Importance

The results of this study indicate that the effects of halothane and isoflurane on EEG activity in the normal horse can be quite variable, even when used in the absence of other drugs. It is recommended that equine EEG be performed without the use of these inhalation anesthetics and that general anesthesia be induced and maintained by other contemporary means.

Molecular signalling pathways in canine gliomas

In this study, we determined the expression of key signalling pathway proteins TP53, MDM2, P21, AKT, PTEN, RB1, P16, MTOR and MAPK in canine gliomas using western blotting. Protein expression was defined in three canine astrocytic glioma cell lines treated with CCNU, temozolamide or CPT-11 and was further evaluated in 22 spontaneous gliomas including high and low grade astrocytomas, high grade oligodendrogliomas and mixed oligoastrocytomas. Response to chemotherapeutic agents and cell survival were similar to that reported in human glioma cell lines. Alterations in expression of key human gliomagenesis pathway proteins were common in canine glioma tumour samples and segregated between oligodendroglial and astrocytic tumour types for some pathways. Both similarities and differences in protein expression were defined for canine gliomas compared to those reported in human tumour counterparts. The findings may inform more defined assessment of specific signalling pathways for targeted therapy of canine gliomas.

Electrophysiologic confirmation of heterogenous motor polyneuropathy in young cats

Background

Reports of motor polyneuropathies in young cats are scarce. Further, in‐depth electrophysiologic evaluation to confirm a motor polyneuropathy in young cats of various breeds other than 2 Bengal cats is lacking.

Hypothesis/Objectives

To confirm a motor polyneuropathy in young cats of various breeds.

Animals

Five young cats with heterogenous chronic or relapsing episodes of weakness.

Methods

Retrospective case series. Cats were presented for evaluation of generalized neuromuscular disease and underwent electrophysiologic examination including electromyography, nerve conduction, and repetitive nerve stimulation. Minimum database and muscle and nerve biopsy analyses were carried out. Descriptive statistics were performed.

Results

Disease onset was at 3 months to 1 year of age and in 5 breeds. The most common clinical sign (5 of 5 cats) was weakness. Additional neurologic deficits consisted of palmigrade and plantigrade posture (4/4), low carriage of the head and tail (4/4), and variable segmental reflex deficits (5/5). Motor nerve conduction studies were abnormal for the ulnar (4/4), peroneal (5/5), and tibial (2/2) nerves (increased latencies, reduced amplitudes, slow velocities). A marked decrement was observed on repetitive nerve stimulation of the peroneal nerve in 3 cats for which autoimmune myasthenia gravis was ruled out. All sensory nerve conduction studies were normal. Histologic evaluation of muscle and nerve biopsies supported heterogenous alterations consistent with motor polyneuropathy with distal nerve fiber loss.

Conclusions and Clinical Importance

Heterogenous motor polyneuropathies should be considered in young cats of any breed and sex that are presented with relapsing or progressive generalized neuromuscular disease.

TP53 mutations in canine brain tumors

The p53 tumor suppressor gene (TP53) is the most frequently altered gene in human cancer. Mutation of the gene has been shown to be an important mechanism of p53 pathway inactivation in a variety of human brain tumors, particularly those of astrocytic origin. Genomic DNA from a series of 37 glial and 51 nonglial canine brain tumors was sequenced to determine the frequency of TP53 gene mutations involving exons 3-9. Exonic mutations were found in 3 of 88 tumors (3.4%) and specifically in 1 of 18 astrocytic tumors (5.5%). This is markedly lower than that reported in comparable human tumors, suggesting that alternative mechanisms of p53 inactivation are likely to be present if p53 function contributes significantly to oncogenesis in canine brain tumors.

Middle ear tumours with brainstem extension treated by ventral bulla osteotomy and craniectomy in two cats

Two geriatric domestic shorthaired cats (DSH) were treated surgically with a ventral bulla osteotomy and craniectomy for middle ear tumours that invaded the calvarium. Both cats had a history of vestibular disease. One cat had a normal neurological examination. Both cats underwent computed tomographic imaging of the head. After intravenous injection of an iodinated contrast material, one cat had a ring-enhancing intracranial lesion and the other had a uniform contrast-enhancing intracranial lesion, which either communicated with the bulla or was associated with bulla osseous lysis/production. One cat had a papillary adenoma and the other had an adenocarcinoma. Both cats had prolonged survivals (630 days; alive and lost to follow-up at 840 days), which is longer than reported in cats with middle ear neoplasia. Craniectomy, in addition to ventral bulla osteotomy, may be part of the treatment plan for middle ear tumours that invade the calvarium.

Expression of receptor tyrosine kinases VEGFR-1 (FLT-1), VEGFR-2 (KDR), EGFR-1, PDGFRalpha and c-Met in canine primary brain tumours

Inhibition of tumour growth and angiogenesis by targeting key growth factor receptors is a promising therapeutic strategy for central nervous system tumours. Characterization of these growth factor receptors in canine primary brain tumours has not been done. Using quantitative real-time TaqMan polymerase chain reaction (PCR), we evaluated the expression of messenger RNA (mRNA) for five tyrosine kinase growth factor receptors (vascular endothelial growth factor receptor [VEGFR]-1, VEGFR-2, endothelial growth factor receptor [EGFR]-1, platelet-derived growth factor receptor a [PDGFRa], and c-Met) relative to normal cerebral cortex in 66 spontaneous canine primary brain tumours. Increased expression of VEGFR-1 and VEGFR-2 mRNA was greatest in grade IV astrocytomas (glioblastoma multiforme) and grade III (anaplastic) oligodendrogliomas. EGFR-1 mRNA expression was more consistently increased than the other receptors in all tumour types, while increased PDGFRa mRNA expression was mostly restricted to oligodendrogliomas. The similarities in increased expression of these tyrosine kinase growth factor receptors in these canine tumours, as compared to data from their human counterparts, suggest that common molecular mechanisms may be present.

Vascular endothelial growth factor mRNA expression and peritumoral edema in canine primary central nervous system tumors

Vascular endothelial growth factor (VEGF) is an important regulator of tumor angiogenesis and vascular permeability, and has been implicated both in progression of central nervous system (CNS) tumors and development of vasogenic peritumoral edema. A retrospective study was done to characterize the levels of expression of the 3 major canine VEGF isoforms (VEGF(120), VEGF(164), VEGF(188)) in a variety of spontaneous canine CNS tumors using quantitative TaqMan reverse transcription real-time polymerase chain reaction. Presence and degree of peritumoral edema also were determined in sampled tumors using magnetic resonance imaging (MRI). Increased expression of VEGF relative to normal cerebral cortex tissue was seen predominantly in high grade astrocytic (grade IV) and oligodendroglial (grade III) tumors, with lower expression in low grade astrocytomas (grade II) and meningiomas (grade I). All 3 major VEGF isoforms were present; VEGF(164) was the predominant isoform, particularly in the tumors with the highest VEGF expression. Peritumoral edema was present in all tumor types; however, a significant association between the extent of peritumoral edema and the level of VEGF expression was not apparent.

Myopathy in horses with pituitary pars intermedia dysfunction (Cushing’s disease)

Fifteen horses with pituitary pars intermedia dysfunction were studied. The horses were of various breeds and between 15 and 28 years of age. Control horses matched for breed and age were studied for comparison. Evaluations included complete blood cell count and serum biochemical analysis, electromyography, and gluteus medius muscle biopsies for histochemical, morphometric, and ultrastructural analysis. No differences were found between groups of horses on routine laboratory analysis or electromyography. We demonstrated that muscle wasting in diseased horses was the result of atrophy of types 2A and 2B muscle fibers and loss of type 2B myofibers. Mild non-specific non-inflammatory myopathic alterations such as myofiber size variation, internal nuclei, perimysial, endomysial and sarcoplasmic fat accumulation were observed. At the ultrastructural level, subsarcolemmal mitochondrial accumulation and increased lipid droplets were evident. Similar to other species, this study confirmed atrophy of type 2 fibers as the cause of muscle mass loss in horses with Cushing's disease.

Glioblastoma multiforme: clinical findings, magnetic resonance imaging, and pathology in five dogs

Although glioblastoma multiforme (GBM), a World Health Organization grade IV astrocytoma, is the most common primary brain tumor in humans, in dogs GBM is relatively rare, accounting for only about 5% of all astrocytomas. This study presents combined clinical, neuroimaging, and neuropathologic findings in five dogs with GBM. The five dogs, aged from 5 to 12 years, were presented with progressive neurologic deficits that subsequent clinical neurologic examination and neuroimaging studies by magnetic resonance imaging (MRI), localized to space occupying lesions in the brain. MRI features of the tumors included consistent peritumoral edema (n = 5), sharp borders (n = 4), ring enhancement (n = 3), heterogenous T2-weighted signal intensity (n = 3), iso- to hypointense T1-weighted images (n = 5), necrosis (n = 5), and cyst formation (n = 2). Two tumors were diagnosed clinically using a computed tomography-guided stereotactic biopsy procedure. At necropsy all the tumors resulted in, on transverse sections, a prominent midline shift and had a variegated appearance due to intratumoral necrosis and hemorrhage. Histologically, they had serpentine necrosis with glial cell pseudopalisading and microvascular proliferation, features which distinguish human GBM from grade III astrocytomas. Immunoreactivity of tumor cells for glial fibrillary acidic protein was strongly positive in all cases, whereas 60% and 40% of the tumors also expressed epidermal growth factor receptor and vascular endothelial growth factor, respectively. These canine GBMs shared many diagnostic neuroimaging, gross, microcopic, and immunoreactivity features similar to those of human GBMs.

Granular cell tumor of the canine central nervous system: two cases

Although pure granular cell tumors have been reported in various sites in the dog, only one tumor has been reported in the central nervous system. Two dogs presented with neurologic signs had brain lesions detected by magnetic resonance imaging in the area of the olfactory bulbs and frontal cortex. In both dogs, a clinical diagnosis of a granular cell tumor was made from tissues obtained from stereotactic biopsies guided by computed tomography. Surgical removal of the tumors was followed by histopathologic, ultrastructural, and immunocytochemical characterization. Although not conclusive, these studies indicated that the granular cells were not of leucocyte origin but may have been derived from the meninges. One dog died 12 months after surgery, and the other was alive 4 months later.

Radiation induced vertebral osteosarcoma following treatment of an intradural extramedullary spinal cord tumor in a dog

A 2-year-old neutered female Rottweiler diagnosed with an intradural extramedullary spinal cord tumor at T12-T13 was successfully treated with cytoreductive surgery followed by Cobalt 60 teletherapy. The dog was euthanised 5-and-a-half years later following diagnosis of an osteosarcoma involving the L1 and L2 vertebrae. Evidence of the initial tumor was not present at necropsy. The vertebral neoplasm fulfilled all of the accepted criteria for a radiation induced tumor. It was concluded that adjunctive irradiation should be considered for treatment of intradural extramedullary tumors of young dogs when total surgical resection is not possible. Although tumor induction is a rare late effect of radiation therapy, the risk of this occurrence should be considered when irradiating young animals. Radiation induced tumors in dogs have been associated with coarse fractionation schemes, or when large intraoperative doses have been administered. A lower dose per fraction, e.g., 3 Gy/fraction or less, is advisable when irradiating young dogs or any dog in which the life expectancy is 3-5 or more years after irradiation.

Intervertebral disc extrusion in six cats

Existing reports concerning intervertebral disc disease (IVDD) have focused almost exclusively on dogs, although a small number of individual case reports of IVDD of cats has been published. The medical records of six cats with IVDD were reviewed. Radiographic studies confirmed narrowed intervertebral disc spaces, mineralised intervertebral discs, and one or more extradural compressive lesions of the spinal cord in each cat. All disc extrusions were located in the thoracolumbar region. Surgical decompression of the spinal cord was achieved in all cats by means of hemilaminectomy and removal of compressive extradural material confirmed to be degenerative disc material. Good to excellent neurological recovery was noted in five of the six cats included in this report. Based on this review, it appears that IVDD of cats has many similarities to IVDD of dogs, and that healthy cats with acute intervertebral disc extrusion(s) respond favourably to surgical decompression of the spinal cord.

Primary canine and feline nervous system tumors: intraoperative diagnosis using the smear technique

The recent application of neuroimaging techniques in veterinary neurology has led to the accurate localization of many types of intracranial lesions but has also created a clinical need, particularly with brain tumors, for a specific intraoperative diagnosis. For human brain tumors, a smear technique has been used successfully for many years to provide an extremely rapid, highly accurate intraoperative diagnosis. In similar smear preparations of intracranial lesions, obtained either by computed tomography (CT)-guided stereobiopsy or from a craniotomy, we have described distinguishing cytologic features of some primary spontaneous nervous system tumors in 80 dogs and 13 cats. A final diagnosis was confirmed by evaluation of paraffin-embedded sections from the same sample and, when appropriate, by immunocytochemical staining. Preliminary findings indicate that, in dogs and cats, this procedure is useful for rapid, accurate intraoperative diagnosis of many primary nervous system tumors. The distinguishing features of the canine and feline tumors bear a remarkably close resemblance to their human counterparts.

Clinical and pathologic features of oligodendrogliomas in two cats

Two oligodendrogliomas in two domestic cats involved mainly the rostral brain stem, midbrain, fourth ventricle, and cerebellum. Both cats were aged neutered males presenting with clinical neurologic deficits suggestive of a brain stem lesion. Magnetic resonance imaging of both tumors demonstrated lesions with a pattern of heterogeneous contrast enhancement and multifocal lesions in one cat. Routine cerebrospinal fluid analysis was normal in one cat and suggestive of an inflammatory disease in the other. Oligodendroglioma cells were seen in cytospin preparations of cerebrospinal fluid from both cats. In each cat, the tumors occurred intraventricularly in the midbrain and fourth ventricle with aggressive intraparenchymal infiltration. There was extensive growth into the basilar subarachnoid space of the midbrain and brain stem in one cat. One tumor was well differentiated, and the other was an anaplastic subtype. Immunostaining for several myelin- and oligodendroglia-specific antigens was negative with formalin-fixed tumors and with unfixed frozen samples from one cat. In both tumors, component cells of the intratumoral vascular proliferations were positive for human von Willebrand factor VIII antigen or smooth muscle actin. Immunocytochemical reactivity for glial fibrillary acidic protein identified both reactive astrocytes and a subpopulation of minigemistocytes in both tumors. Ultrastructurally, the tumor cells were unremarkable except for their prominent desmosomal junctions and paucity of microtubules.

Reversible magnetic resonance imaging abnormalities in dogs following seizures

Reversible magnetic resonance (MR) imaging lesions have been described in humans following seizures. This condition has not yet been reported in animals. This paper describes reversible abnormalities identified in 3 dogs using MR imaging that was performed initially within 14 days of the last seizure and follow-up imaging that was performed after 10 to 16 weeks of anticonvulsant therapy. All three dogs had lesions in the piriform/temporal lobes, characterized by varying degrees of hyperintensity on T2-weighted images and hypointensity on T1-weighted images. In one dog, contrast enhancement was evident. On reevaluation, partial resolution occurred in all 3 dogs. In a fourth animal with an olfactory meningioma, similar appearing lesions in the temporal cortex and right and left piriform lobes were identified after seizure activity. A surgical biopsy of the temporal cortex and hippocampus was performed and edema, neovascularization, reactive astrocytosis, and acute neuronal necrosis were evident. These histologic findings are similar to those reported in humans with seizures. Recognizing the potential occurrence of reversible abnormalities in MR images is important in developing a diagnostic and therapeutic plan in canine patients with seizures. Repeat imaging after seizure control may help differentiate between seizure-induced changes and primary multifocal parenchymal abnormalities.

Current concepts in the diagnosis and treatment of brain tumours in dogs and cats

Intracranial tumours occur relatively frequently in dogs, and less commonly in cats. With the availability of computed tomography (CT) and magnetic resonance imaging, more accurate determination of the location and extent of brain tumours in companion animals has become possible. Following these advances in imaging, precise CT-guided stereotactic techniques for both tumour biopsy and intratumoral drug delivery have been developed for use in cats and dogs. Also, tumour identification methods, such as crush preparation examination, have facilitated rapid tumour identification. The use of improved diagnostic techniques has resulted in an increasing demand for effective therapies for brain tumours. While surgical removal and irradiation remain important treatment considerations in the management of brain tumours of cats and dogs, the development of gene therapy strategies for treatment of intracranial tumours offers much promise, although research in this area is still at an early stage.

Modification and application of a Pelorus Mark III stereotactic system for CT-guided brain biopsy in 50 dogs

The Pelorus Mark III Stereotactic System is a commercially available device for CT-guided stereotactic brain biopsy in people. With relatively minor modifications, this device was used to safely and accurately perform CT-guided stereotactic brain biopsies in 50 dogs with intracranial lesions. Modifications were necessary to accommodate a 90 degree shift in orientation of the canine head compared to the human head during the imaging phase of the procedure, and to facilitate other phases of the biopsy procedure that are affected by the uneven and variable topography of the canine skull. Description of a typical CT-guided brain biopsy procedure in dogs using the modified Pelorus Mark III Stereotactic System is provided. Accuracy of biopsy needle placement was determined by comparing the x, y and z coordinates of the biopsy target site with the actual coordinates of the needle tip on CT images. Mean needle placement error was 3.5 +/- 1.6 mm. Needle placement error was not significantly related to operator experience, dog size (body weight), or needle path length, however, needle placement error was significantly affected by lesion location.

CT-guided brain biopsy using a modified Pelorus Mark III stereotactic system: experience with 50 dogs

This report describes the results of CT-guided stereotactic brain biopsies performed on 50 consecutive dogs using a modified Pelorus Mark III Stereotactic System. Based on available histopathologic samples (stereotactic biopsy [n = 50], surgery [n = 17], necropsy [n = 9]) the patient population consisted of 34 dogs with primary brain tumors, 2 with invasive nasal adenocarcinomas, and 13 with non-neoplastic brain lesions. Brain tissue was not obtained from one dog. In 22 dogs a final diagnosis was made from tissue subsequently obtained from surgical resection or at necropsy. The final diagnosis was in agreement with the stereotactic biopsy diagnosis in 20 of these 22 dogs. In 17 other dogs without follow-up, stereotactic biopsy provided a diagnosis of a specific primary brain tumor subtype. Postoperative complications associated with the biopsy procedure were assessed in 41 dogs. The other 9 dogs either went directly to surgery (n = 7) or were killed (n = 2) immediately after the biopsy procedure. Thirty-six dogs recovered without apparent clinical complications. Postoperative clinical complications in the remaining 5 dogs included transient epistaxis (1 dog), transient exacerbation of cerebellar signs (1 dog), obtundation progressing to coma (1 dog), and medically uncontrollable seizures (2 dogs). The latter 3 dogs with severe neurologic complications all had large primary brain tumors and had been receiving high doses of phenobarbital and glucocorticoids to control seizures at the time of biopsy. These results suggest that this CT-guided biopsy procedure can provide an accurate pathologic diagnosis of brain lesions detected by CT and MR neuroimaging. Further refinement of both technique and case selection is expected to reduce the rate of clinical complications and to improve the accuracy of the procedure.

Feline vestibular disorders. Part I: anatomy and clinical signs

An understanding of the anatomy of the feline vestibular system is essential for interpretation of the clinical signs associated with vestibular dysfunction, for precise lesion localisation, and for accurate interpretation of results of diagnostic imaging. Appropriate recognition and interpretation of the clinical signs of vestibular disease is also an essential aspect of the precise diagnosis of the cause of vestibular dysfunction in cats. The objectives of this review are to provide an overview of the anatomy of the feline vestibular system, and to review the clinical signs of peripheral and central vestibular dysfunction of cats.

Feline vestibular disorders. Part II: diagnostic approach and differential diagnosis

Results of a neurological examination usually permit localisation of a vestibular disorder to either the central or peripheral parts of the vestibular system. Many different disorders located in the same part of the vestibular system will produce similar clinical signs. Therefore, additional diagnostic tests beyond a neurological examination are required in order to make an accurate diagnosis. The objectives of this review are to outline a diagnostic approach for disorders affecting the feline vestibular system, and to summarise the clinically important features of frequently diagnosed diseases affecting the vestibular system of cats.

Renal failure, laminitis, and colitis following severe rhabdomyolysis in a draft horse-cross with polysaccharide storage myopathy

A Thoroughbred-Percheron crossbred gelding developed a fulminant cascade of sequelae following a severe episode of rhabdomyolysis. Complications may occur with rhabdomyolysis of any etiology. In warmblood horses with Percheron bloodlines, rhabdomyolysis may be secondary to polysaccharide storage disease, and aggressive therapy should be undertaken promptly to avoid the complications.

Late-onset progressive spinocerebellar degeneration in Brittany Spaniel dogs

Eight Brittany Spaniel dogs, seven females and one male, between 7 and 14 years old presented with clinical neurological signs of spinocerebellar disease of about 6 months to 4 years duration. Clinically the dogs had a dramatic forward "saluting" movement of the thoracic limbs, hypermetria of the pelvic limbs, cerebellar ataxia and intention tremors. Terminally, dogs crawled in a crouched thoracic posture with neck extension. Lesions were confined to cerebellum, medulla oblongata and spinal cord. The most severe lesion was diffuse Purkinje cell loss with massive neurofilament accumulation in degenerating cells. There was some bilateral neuronal degeneration in the dorsal horns of the spinal cord and in the gracilis and cuneate nuclei. There was bilateral sporadic axonal degeneration in the dorsal columns and lateral and ventromedial areas of the spinal cord. The etiology of this syndrome was not determined.

Central nervous system disorders after renal transplantation in cats

OBJECTIVE

This study describes the incidence and severity of postoperative central nervous system (pCNS) disorders in feline renal transplant recipients.

STUDY DESIGN

A retrospective study based on the medical records of cats that received renal allografts from 1987 to 1996.

ANIMALS OR SAMPLE POPULATION

Fifty-seven client-owned cats received renal allografts for the treatment of renal failure.

METHODS

The frequency, duration, severity, and treatment of episodes of pCNS disorders were recorded from the medical records.

RESULTS

Twelve (21%) of 57 cats had pCNS disorders 1 hour to 5 days after the surgical procedure. Seven cats survived; four had single or multiple seizure episodes, and two had seizure episodes or disorientation followed by a period of coma. One cat became temporarily ataxic and blind after restraint for venipuncture. Five cats died; all had episodes of disorientation or seizures, or both, that progressed to a nonrecoverable comatose state, respiratory arrest or cardiac arrest, or both. There were no significant differences between the two groups in preoperative serum creatinine, blood urea nitrogen, or cholesterol levels, and intraoperative blood pressure measurements. There were no significant differences in the postoperative serum glucose levels, electrolytes levels, or osmolality between the two groups. The cats with pCNS disorders had a mean preoperative trough cyclosporine A (CyA) whole blood level of 429 ng/mL; cats without pCNS disorders had a significantly (P = .0116) higher mean preoperative trough CyA whole blood level of 736 ng/mL.

CONCLUSION

Central nervous system disorders are a common and often fatal complication of renal transplantation in cats.

CLINICAL RELEVANCE

Recognition of pCNS disorders, and possible causes, will help develop hypotheses to investigate the problem.

Magnetic resonance imaging and computed tomography characteristics of intracranial intra-arachnoid cysts in 6 dogs

Magnetic resonance imaging (MRI) and computed tomographic imaging (CT) characteristics of intracranial intra-arachnoid cysts in six dogs are described. Of the six dogs, three were less than one year of age and 4 were males. Five of the six dogs weighed less than 11 kg. Five cysts were located in the quadrigeminal cistern. On CT images, the intracranial intra-arachnoid cysts had sharply defined margins, contained fluid isodense to CSF and did not enhance following i.v. administration of contrast. On MRI images, the intracranial intra-arachnoid cysts were extra-axial, contained fluid isointense with CSF and did not enhance following i.v. contrast. While spinal arachnoid cysts of dogs have been reported in the literature, other than the six dogs contained in this report, intracranial intra-arachnoid cysts have not to our knowledge been described in animals. These six dogs have a similar age, sex, history, clinical signs, CT and MRI findings to those reported in people with intracranial intra-arachnoid cysts.

Sensory nerve conduction velocity of the caudal cutaneous sural and medial cutaneous antebrachial nerves of adult horses

Maximal conduction velocities of compound action potentials evoked by stimuli of 2 times threshold in the caudal cutaneous sural (CCSN) and medial cutaneous antebrachial (MCAN) nerves were determined by averaging potentials evoked and recorded through percutaneous needle electrodes. Mean maximal conduction velocities of compound action potentials were: CCSN = 61.3 +/- 2.0 meters/second (m/s) and MCAN = 56.4 +/- 2.8 m/s. To confirm accuracy of our percutaneous recordings, compound action potentials were recorded through bipolar chlorided silver electrodes from the exposed surfaces of fascicles of the CCSN and the MCAN. The maximal conduction velocities of these potentials were in agreement with the conduction velocities of compound action potentials that were evoked and recorded through percutaneous needle electrodes. The specificity of stimulating and recording sites was verified by recording before and after section of the nerves. Stimuli from 3 to 5 times threshold evoked a second, longer latency, compound action potential that consisted of a variable number of components in the CCSN and MCAN. The configurations and conduction velocities of the shorter latency potentials were the same as those of the single compound action potentials evoked by stimuli of 2 times threshold. Mean conduction velocities of the longer latency potentials were: CCSN = 24.4 +/- 2.6 m/s and MCAN = 24.5 +/- 2.2 m/s. Needle electrode and direct stimulation of either the CCSN or the MCAN at 3 to 5 times threshold failed to evoke contractions of limb muscles. Therefore, action potentials that contributed to the evoked compound potentials recorded in these horses arose, most likely, from afferent nerve fibers.

Comparison of computed tomography and radiography for detecting changes induced by malignant nasal neoplasia in dogs

The ability of computed tomography and radiography to detect changes associated with nasal neoplasia was compared in dogs. Eighteen areas or anatomic structures were evaluated in 21 dogs for changes indicative of neoplasia. Computed tomography was superior (P < or = 0.05) to radiography for detecting changes in 14 of 18 areas. Radiography was not superior for detecting changes in any structure or area. Computed tomography reveals vital information not always detected radiographically to assist in providing a prognosis and in planning treatment for nasal neoplasms in dogs.

Diagnosis of cauda equina abnormalities by using electromyography, discography, and epidurography in dogs

Electromyography (EMG), L7-S1 discography and epidurography were investigated in 15 dogs with clinical signs of cauda equina dysfunction and in 7 control dogs without such clinical signs. Electromyography of paraspinal and pelvic limb muscles was done in 13 of 15 affected dogs. An L7-S1 discogram followed by an epidurogram was performed in all 22 dogs using 20% iopamidol. Results of discograms, epidurograms, and gross necropsy examinations were normal in six of seven control dogs. The one dog in which these studies were abnormal had a mild L7-S1 disc protrusion that did not result in nerve root compression at necropsy. Electromyographic analysis was 100% accurate in predicting the presence or absence of cauda equina disease. None of the results of discograms were falsely negative. Twelve of 15 discograms in clinically affected dogs indicated dorsal disc protrusion, but 2 of these protrusions were found to be noncompressive at surgery (13% error). Abnormal epidurograms occurred in 9 of 15 clinically affected dogs. There was one false positive and two false negatives (20% error). Electromyography was a sensitive screening technique for the presence of cauda equina disease. Discography may be more sensitive for detection of L7-S1 disc protrusion than epidurography. An abnormal radiographic contrast study of the cauda equina may only be useful when combined with an abnormal EMG.

Intracranial meningioma with pulmonary metastasis in three dogs

Extracranial metastasis of primary central nervous system neoplasms is uncommon and has not been described in the dog. We report the clincopathologic features of intracranial meningioma with pulmonary metastasis in three dogs (case No. 1: 13-year-old castrated male Boxer dog; case No. 2: 14-year-old spayed female Dachshund; case No. 3: 6-year-old spayed female German Shepherd Dog). Case No. 1 presented with ataxia, lethargy, vomiting, and leaning and falling to the right, and had a transient remission following radiation and corticosteroid therapy; case No. 2 had a history of seizures that were unresponsive to primidone, left-sided postural reaction deficits, ataxia, and circling to the right; case No. 3 had only intermittent episodes of vomiting Computed tomography of case Nos. 1 and 2 revealed peripherally located homogeneous contrast-enhancing intracranial masses. Postmortem examination revealed intracranial masses with single or multiple pulmonary nodules in all three cases. Histologically, the intracranial and pulmonary masses were meningotheliomatous meningiomas with atypical features including brain infiltration, necrosis, nuclear atypia, prominent nucleoli, and moderate cell density. All of the primary meningiomas had low mitotic rates. The current interest in early diagnosis and aggressive clinical/surgical management of canine patients with meningioma and other primary central nervous system neoplasms will likely result in an increased detection of extracranial metastases.

Chronic cervical compressive myelopathy in horses: patterns of astrocytosis in the spinal cord

The distribution and morphology of fibrous astrocytes in the cervical spinal cord of normal horses and horses with chronic compressive myelopathy were demonstrated using immunohistochemical staining for glial fibrillary acidic protein. In the spinal cord from normal horses, astrocytes with stellate cell bodies and short processes were irregularly distributed in grey matter. In the white matter, their cell bodies were small and angular in areas adjacent to grey matter and larger and more stellate-shaped in the subpial area. Astrocyte processes were fine, and evenly distributed in a predominantly radial pattern in transverse sections of cord. Gliosis was marked in the spinal cords of horses with cervical compressive myelopathy. In the grey matter at the level of compression astrocytes were often enlarged and rounded, with short, blunt processes, but the gliosis was generally mild. In the white matter, gliosis was obvious in areas of nerve fibre swelling and degeneration at the level of compression and in areas of ascending and descending Wallerian degeneration. The fine radial pattern of astrocyte fibres was replaced by a dense, irregular arrangement. Gliosis persisted in the cords of chronically affected horses after active nerve fibre degeneration had subsided. The areas of gliosis coincided with the areas of Marchi staining for degenerating myelin and with areas of myelin loss in osmium tetroxide post-fixed tissue. Histological observations were consistent with astrocytes replacing areas of extracellular space that remained after nerve fibre degeneration. it is concluded that astrocytic gliosis is a prominent and persistent alteration of the spinal cord of horses with chronic cervical compressive myelopathy.

Muscle injury following experimental intraoperative irradiation

The paraaortic region of beagle dogs was irradiated to 15 to 55 Gy intraoperative irradiation, 10 to 47.5 Gy intraoperative irradiation following 50 Gy external beam irradiation in 25 fractions, or 50 to 80 Gy external beam irradiation in 30 fractions. Six MeV electrons were used for intraoperative irradiation, and external beam irradiation was done using photons from a 6 MV linear accelerator. The psoas muscle in the irradiation field was examined histomorphometrically 2 or 5 years after irradiation. The percentage of muscle fibers and capillaries decreased, whereas the percentage of connective tissue increased with increased dose for both intraoperative irradiation only and intraoperative irradiation plus external beam irradiation. The dose causing a 50% decrease in the percentage of muscle fibers was 21.2 Gy and 33.8 Gy at 2 and 5 years, respectively, after intraoperative irradiation alone, and 22.9 Gy and 25.2 Gy at 2 and 5 years, respectively, after intraoperative irradiation combined with 50 Gy external beam irradiation. The ED50 for severe vessel lesions was 19.2 Gy and 25.8 Gy at 2 and 5 years, respectively, after intraoperative irradiation alone and 16.0 Gy and 18.0 Gy at 2 and 5 years, respectively, after intraoperative irradiation combined with 50 Gy external beam irradiation. External beam irradiation alone caused a slight decrease in percentage of muscle fibers with increased dose, and vessel lesions were infrequent or mild. Radiation-induced muscle injury was characterized by loss of muscle fibers, decreased fiber size, severe vessel lesions, hemorrhage, inflammation, coagulation necrosis, and fibrosis. These histopathologic characteristics distinguish this muscle injury from that caused by neurogenic atrophy. These data indicate that radiation-induced muscle injury most likely was caused by injury of the supporting vasculature. The lesions produced were largely a function of the single intraoperative dose rather than the external beam fractionated doses. Furthermore, it appears that 20 to 25 Gy intraoperative irradiation combined with 50 Gy external beam irradiation may be near the maximum tolerated dose by sublumbar musculature and its supporting vasculature.

Trabecular bone remodeling and bone mineral density in the adult cat during chronic dietary acidification with ammonium chloride

Ammonium chloride (NH4Cl) is used as a urinary acidifier in the treatment and prevention of feline urologic syndrome. It is reported to cause alterations in calcium and bone metabolism in humans, dogs, and rats. Adult cats with normal renal function were fed 1.5% NH4Cl for 6 months to study the effects of chronic dietary acidification on trabecular bone remodeling of the iliac crest and bone mineral density (BMD) of lumbar vertebral trabecular bone and femoral cortex. Histomorphometric analyses of iliac crest biopsies were performed before and after treatment. Static and dynamic parameters of bone resorption and formation were determined. Single-energy quantitative computed tomography (SEQCT) was used to measure lumbar trabecular and femoral cortical BMD. There were no significant treatment effects in iliac crest trabecular bone remodeling or BMD of the vertebrae and femora. Bone remodeling activity decreased with time in both acidotic and control cats. Vertebral BMD increased with time in both groups of cats, whereas no change was seen in the femora. Thus, chronic dietary acidification for 6 months with therapeutic levels of NH4Cl produced no significant changes in trabecular bone remodeling or bone mineral density in adult cats.

Multilobular osteochondrosarcoma of the canine skull: 16 cases (1978-1988)

The medical records of 12 dogs with multilobular osteochondrosarcoma (MLO) and examined at the Veterinary Teaching Hospital, Colorado State University from August 1979 to January 1987 were reviewed. Medical records of 1 dog with MLO and 3 dogs with MLO examined at the Ontario Veterinary College, University of Guelph and the Veterinary Medical Teaching Hospital, University of California, Davis, respectively, were also reviewed and included in the study. The mean age of affected dogs was 7.5 years, a single breed did not appear to be overrepresented, and males were affected as frequently as were females. All of the primary lesions affected either the mandible, maxilla, or cranium. Excision was the only treatment in 11 dogs, 2 dogs had radiotherapy in addition to excision, and 1 dog had radiotherapy and chemotherapy after excision. Twelve treated dogs had follow-up information available. Of the 12 treated dogs, 7 (58%) had local recurrence, with median time to recurrence of 14 months. Seven dogs (58%) developed metastatic disease after treatment, with median time to metastasis of 14 months. The median disease-free interval was 12 months, and the median survival time was 21 months. Excision with histologically complete surgical margins appeared to offer good opportunity for long-term tumor control. The role of adjuvant chemotherapy and radiotherapy in the management of MLO remains unclear.

Clinical management of epilepsy of dogs and cats

A logical approach to the clinical management of a dog or cat with a history of seizures caused by epilepsy is presented. The definition of epilepsy, the classification of epileptic seizures, and the causes of seizures are discussed. A diagnostic approach to dogs and cats with seizure disorders is outlined. Anticonvulsant therapy for epilepsy is discussed, including the objectives of therapy, decision to start therapy, selection of an anticonvulsant drug, monitoring anticonvulsant therapy, and anticonvulsant drug failure.

Bone necrosis and tumor induction following experimental intraoperative irradiation

The bone of the lumbar vertebrae of 153 dogs was examined 2 and 5 years after intraoperative irradiation (IORT), fractionated external beam irradiation (EBRT), or the combination. Groups of dogs received 15 to 55 Gy IORT only, 10 to 47.5 Gy IORT combined with 50 Gy EBRT in 2 Gy fractions or 60 to 80 Gy EBRT in 30 fractions. Six MeV electrons were used for IORT, and EBRT was done using photons from a 6 MV linear accelerator. The paraaortic region was irradiated and the ventral part of the lumbar vertebrae was in the 90% isodose level. Two years after irradiation, the dose causing significant bone necrosis as determined by at least 50% empty lacunae in the vertebral cortex was 38.2 Gy IORT alone and 32.5 Gy IORT combined with EBRT. Five years after irradiation, the dose causing 50% empty lacunae was 28.5 Gy IORT only and 14.4 Gy IORT combined with EBRT. The ED50 for lesions of the ventral vertebral artery was 21.7 Gy IORT only and 20.1 Gy IORT combined with 50 Gy EBRT 2 years after irradiation and 27.0 Gy IORT only and 20.0 Gy IORT combined with 50 Gy EBRT 5 years after irradiation. All lesions after EBRT only were mild. Eight dogs developed osteosarcomas 4 to 5 years after irradiation, one at 47.5 Gy IORT only and the remainder at 25.0 Gy IORT and above combined with 50 Gy EBRT. In conclusion, the extent of empty lacunae, indicating bone necrosis, was more severe 5 years after irradiation than after 2 years. The effect of 50 Gy EBRT in 2 Gy fractions was equivalent to about 6 Gy IORT 2 years after irradiation and to about 14 Gy 5 years after irradiation. Based on these estimates, IORT doses of 10 to 15 Gy have an effect 5 times or greater than the amount given in 2 Gy fractions. Osteosarcomas occurred in 21% of dogs which received doses greater than 25 Gy IORT. Doses of 15 to 20 Gy IORT in combination with 50 Gy EBRT in 2 Gy fractions may be near the tolerance level for late developing bone injury.

Peripheral neuropathies following experimental intraoperative radiation therapy (IORT)

Injury to peripheral nerves in the lumbar para-aortic region was evaluated in beagle dogs 2 years following fractionated irradiation (EBRT), intraoperative irradiation (IORT), or a combination of IORT and EBRT. Time to onset of peripheral neuropathy was determined by means of serially completed neurological and electrophysiological examinations. Peripheral neuropathies were seen beginning as early as 6 months following 35 Gy (or greater) IORT only and 35 Gy plus 50 Gy EBRT. The incidence of peripheral neuropathies increased with increasing IORT doses beginning at 15 Gy. Onsets of peripheral neuropathies following IORT alone were clustered between 6 and 18 months, with onset in some dogs occurring as late as 24 months. The combination of IORT and EBRT resulted in an incidence and latency to onset of neuropathies similar to that seen with IORT alone. Neuropathies were not seen with EBRT alone at doses from 50 Gy to 80 Gy. Recovery of nerve function did not occur in affected dogs. Histological studies of nerves 2 years following irradiation demonstrated loss of axons and myelin, with a corresponding increase in endoneurial, perineurial, and epineurial connective tissue. Percentage of axon and myelin decreased to about 60% of normal at 15 Gy IORT, and additionally at higher doses. An insignificant decrease in percentage of axon and myelin was seen following EBRT alone. A significant lesion occurring in and around nerves at most IORT doses was necrosis and hyalinization of the media of small arteries and arterioles. The dose for a 50% probability for causing severe vessel lesions in the 2-year study was 19.5 Gy IORT only and 18.7 Gy when IORT was combined with EBRT. These lesions were not seen with any EBRT only dose. These studies suggest that peripheral nerve is a dose limiting normal tissue in IORT. Neuropathies appear to result from direct effects of irradiation on nerve and secondary effects to nerve resulting from damage to regional vasculature.

Central nervous system toxicosis associated with metronidazole treatment of dogs: five cases (1984-1987)

Metronidazole, administered to 5 dogs for periods ranging from 3 to 14 days, was associated with acute development of CNS dysfunction. Metronidazole dosage ranged from 67.3 to 129.0 mg/kg of body weight/d. Clinical signs of toxicosis began with anorexia and intermittent vomiting and progressed rapidly to include pronounced, generalized ataxia and vertical, positional nystagmus. These signs were consistent with lesions of the vestibular nuclei and/or cerebellum. High CSF protein content was detected in 2 of 3 dogs from which CSF was collected. Two dogs were euthanatized because of severe neurologic dysfunction. Three dogs improved slowly and recovered completely over several months. These findings suggest that currently recommended dosages of metronidazole may be too high for some dogs.

Hypokalemia in cats: 186 cases (1984-1987)

Retrospective review of serum biochemical data obtained from 501 cats over a 3-year period (1984-1987) indicated that 186 (37%) had hypokalemia (serum potassium concentration less than 4.1 mEq/L). After adjusting for disease diagnosis, cats fed either of 2 commercial diets were 4 times more likely to be hypokalemic than cats fed other diets. Odds ratios (OR; measure of association), adjusted for diet type, were calculated to determine the odds of hypokalemia for a given disease, compared with odds of normokalemia for the same disease. Chronic renal failure (OR = 14.4), hepatic disease (OR = 5.7), systemic infectious diseases (viral or bacterial; OR = 2.7), and neuromuscular or CNS disease (OR = 2.4) were all significantly associated (P less than 0.05) with the occurrence of hypokalemia. Significant differences in age or sex between hypokalemic and normokalemic cats were not found. Within the group of 186 hypokalemic cats, hypercholesterolemia (89 cats; 48%), hyperglycemia (88 cats; 47%), high serum urea nitrogen concentration (86 cats; 46%), hyperchloridemia (80 cats; 43%), and high serum creatinine concentration (73 cats; 39%) were the most common biochemical abnormalities. When disease diagnosis was compared among cats with severe hypokalemia (serum potassium concentration less than 3.0 mEq/L) and those with moderate hypokalemia, cats with severe hypokalemia were 3.5 times more likely to have chronic renal failure than cats with less severe hypokalemia.(ABSTRACT TRUNCATED AT 250 WORDS)

Intraspinal epidermoid cyst in a dog

A 2-year-old female Rottweiler was examined because of progressive gait deficits consistent with transverse myelopathy between the T2 and L3 spinal cord segments. Myelography confirmed an intramedullary spinal cord lesion between T13 and L1, so the dog was euthanatized. At necropsy, an intramedullary epidermoid cyst was confirmed in the T13 and L1 spinal cord segments. The epidermoid cyst probably resulted from a congenital cause.

Central nervous system infection associated with anaerobic bacteria in two dogs and two cats

Central nervous system (CNS) infection caused by anaerobic bacteria (including Bacteroides, Fusobacterium, Peptostreptococcus, and Eubacterium) was diagnosed in two dogs and two cats. In one dog there was extensive meningomyeloencephalitis, presumably the result of hematogenous spread of bacteria from lung abscesses and bacterial endocarditis. Subdural empyema of unknown origin was found in a second dog and two cats. Clinical signs in all four animals included mental depression and focal neurologic deficits, without fever.

Neurotoxicity of amphotericin B methyl ester in dogs

Clinical and neuropathologic effects of chronically administered intravenous (iv) amphotericin B methyl ester (AME) were observed in 3 male dogs (2 German shorthaired pointers and 1 pit bull). Each dog received 6.2-7.3 g of AME (299-327 mg/kg body weight) over a period of 11-12 weeks. One dog developed neurologic signs of severe diffuse brain dysfunction and at necropsy all 3 dogs had a marked leukoencephalopathy, most severe in centrum ovale and subcortical white matter of frontal lobes. Brain histopathology included diffuse myelin loss, oligodendrocyte depletion, accumulation of macrophages filled with sudanophilic lipid, fibrillary astrogliosis, and swelling or fragmentation of many axons. Two control dogs administered iv glucose showed no neuropathologic abnormalities. These findings closely resemble the clinical and neuropathologic abnormalities that developed in patients during the first human trial of AME for treatment of fungal infections, but differ from those of animal studies that did not closely simulate the long-term drug administration required for antifungal therapy in humans. It was concluded that before human clinical trial is authorized, experimental protocols for animal studies of drug toxicity should reflect the anticipated human use of the drug, both in dose and duration.

Potassium depletion in cats: hypokalemic polymyopathy

Generalized weakness of acute onset, apparent muscular pain, and persistent ventroflexion of the neck were observed in 6 cats. These clinical signs were associated with a low serum potassium concentration and high serum creatine kinase activity. Generalized electromyographic abnormalities, together with normal motor nerve conduction velocity determinations, were detected in all cats. Muscle biopsy specimens from 4 of 5 cats were not abnormal on light microscopic examination. Mild necrosis and infrequent macrophages were evident in a muscle biopsy specimen from one cat. Signs of polymyopathy resolved in all cats, and creatine kinase activities returned to the normal range after parenteral and oral administration of potassium. Polymyopathy and hypokalemia recurred in 3 cats in which dietary potassium supplementation was not maintained after initial recovery from hypokalemic polymyopathy.

Potassium depletion in cats: renal and dietary influences

Excessive urinary potassium loss was diagnosed in 7 cats with persistent hypokalemia and high serum creatinine concentrations. Renal tubular acidosis (proximal or distal) was not evident in the affected cats. Plasma aldosterone concentrations and plasma renin activities in affected cats were not significantly different from control values. Potassium depletion and hypokalemia were attributed to the combined effects of decreased dietary potassium intake and excessive urinary potassium losses. It was concluded that increased urinary potassium excretion may represent a basic response to renal dysfunction in cats. Data suggested that dietary potassium supplementation improved renal function in most cats in this study.