Multicentric nerve sheath fibrosarcomas of multiple cranial nerve roots in two dogs

Nerve sheath fibrosarcomas of the left 5th through 8th cranial nerve roots were diagnosed in 1 dog and of the left 4th through 8th cranial nerve roots in another dog. Clinical signs in both dogs included head tilt to the left, circling to the left, left hemiparesis and proprioception deficits, rotary nystagmus, left-sided atrophy of masticatory muscles, and cutaneous hypalgesia of the left side of the face. Cranial nerve roots from both dogs were incorporated in discrete, firm, encapsulated, lobulated, tan masses of various sizes that compressed adjacent brain stem and cranial nerves. There were no regional or distant metastases; however, there was enlargement of nerve roots adjacent to the masses. The masses were composed of bundles and sheets of anaplastic, polymorphic to spindle-shaped cells that infiltrated cranial nerves and ganglia and extended into the brain along nerve roots. Masses contained various amounts of collagen and reticulin fibers, but no mucopolysaccharide ground substance. There was no myelin or S-100 protein associated with neoplastic cells. The tumors appeared to have a multicentric origin from cranial nerve sheaths.     

Evaluation of repetitive nerve stimulation in young dogs

Evaluation of neuromuscular transmission requires a complete electrodiagnostic evaluation including repetitive nerve stimulation. Supra-maximal stimulation of the peroneal nerve and recording of the compound muscle action potentials from the cranial tibial muscle were under-taken in 25 young dogs of two to 18 months of age. Proximal stimulation in the trochanteric fossa and distal stimulation in the popliteal fossa were chosen for small and large breeds, respectively. Highly consistent results were obtained when the examined muscle was kept at a constant temperature and the limb was firmly fixed. Neither sex- (14 females, 11 males) nor age- related (mean = 4·4 months] differences in neuromuscular transmission were found, but frequency-dependent phenomena were observed. These became more distinct with high frequency stimulation. Pseudofacilitation (n = 16/15 Hz; n = 7/50 Hz), was found to range within certain limits (6 to 26 per cent/15 Hz; 13 to 31 per cent/50 Hz). Its mean values at 50 Hz stimulation were apparently higher (26·88 per cent) than those at 15 Hz stimulation (11·3 per cent). Decremental responses occurred mainly with application of tetanic stimulation frequency (n = 1/15 Hz; n = 12/50 Hz) and may represent blocking of neuromuscular transmission. Each of these reaction patterns usually started to occur at the fourth potential of a series (81 per cent/15 Hz; 94 per cent/50 Hz) and remained constant during the second half of the stimulation train in most cases. The occurrence of post-tetanic phenomena in healthy dogs is poorly understood. Post-tetanic potentiation observed in the present material (24 per cent) may represent pseudofacilitation following high stimulation frequency (50 Hz/100 pulses).     

Confirmation of epidural needle placement using nerve stimulation in dogs

Caudal epidural anesthesia is useful when anesthesia of the lumbar and sacral dermatomes is needed. Its success relies on the proper placement of the needle in the epidural space. However, accurate positioning of the needle can be difficult in certain patients (i.e.obesity). The purpose of this preliminary study was to document the use of nerve stimulation as a means of confirming accurate needle positioning in the epidural space prior to drug administration. Twenty large breed dogs undergoing hindlimb or perineal surgery were enrolled. Following induction of general anesthesia, patients were prepared for routine epidural drug administration. A 17 ga, 3.5” shielded Tuohy needle was used and was connected to a peripheral nerve stimulator set to deliver a current at 1 Hz, with a pulse width of 0.2 m sec. Initial current was set at 1.2 mA as the needle was advanced into position. Confirmation of epidural needle placement was confirmed when twitches were observed in the hindlimbs and/or tail. Current setting was then decreased incrementally by 0.2 mA until no further twitches were observed. Success of epidural drug placement was confirmed subjectively by motor blockade to the blocked dermatomes and clinical signs of balanced anesthesia (lack of sympathetic response to surgical stimulation while maintained at light plane of anesthesia). Lowest mean (range) current to elicit hindlimb twitches was 0.72 mA (0.4–1.0 mA). Lowest mean (range) current to elicit tail twitches was 0.58 mA (0.4–1.0 mA). Tail twitches were reliably lost at mean current of 0.37 mA (0.2–0.8). Epidural anesthesia was considered to be successful in 19/20 dogs. In only 9/20 dogs, needle placement would have been correct based on using ‘classic’ indicators alone (‘pop’ as enter epidural space, loss of resistance to injection). The results of this study suggest that nerve stimulation may be useful in confirming correct epidural needle placement prior to drug administration.     

The normal response to repetitive motor nerve stimulation in dogs

The responses of certain muscles to stimulation at different frequencies has been studied in normal dogs. Repetitive stimulation at 10 and 20 Hz resulted in a smooth, progressive decremental response when the compound muscle action potential (CMAP) was recorded from the plantar, and to a lesser extent the palmar, interosseous muscles. In contrast, there was a slight incremental response when the CMAP was recorded from the cranial tibial muscle. Studies using a competitive neuromuscular blocking agent have suggested that the plantar interosseous muscles have a greater proportion of low efficacy synapses in comparison with the other muscles studied. The cranial tibial muscle may therefore be more suitable for assessing neuromuscular transmission than the distal limb muscles.     

Influence of electrical stimulation on regeneration of the radial nerve in dogs

The effects of biphasic electric fields on nerve regeneration that follows injury to the left radial nerve were studied in dogs by electromyography (EMG). Left and right radial nerves were crushed with a serrated haemostat. Stimulating electrodes were positioned proximally and distally to the site of the injury. The left nerves received rectangular, biphasic and current pulses (30 microA, 0.5 Hz) through the injury for two months. The right radial nerves were treated as controls and regenerated without electrical stimulation. EMG activities were recorded intramuscularly from the left and right musculus extensor digitalis communis (MEDC). Results obtained at the end of the two-month stimulation period showed a significant difference in EMG activity between the left (stimulated) and the right (non-stimulated) MEDC, suggesting that electrical treatment enhanced nerve regeneration.     

Cortical averaged evoked potentials produced by pudendal nerve stimulation in dogs

Averaged evoked potentials were recorded from the scalp of 22 dogs after repetitive stimulation of the pudendal nerve. Four experimental procedures were used: (1) percutaneous needle-stimulating electrodes with dogs tranquilized with xylazine; (2) percutaneous needle-stimulating electrodes with dogs tranquilized with acepromazine; (3) percutaneous needle-stimulating electrodes with dogs anesthetized with alpha-chloralose; and (4) Sherrington type stimulating electrodes applied directly to nerves with dogs anesthetized with alpha-chloralose. The average evoked potentials were similar with all treatments. Three peaks (N1, P1, and N2) with consistent latency and amplitude were generally present, followed by additional peaks with variable latencies and amplitudes. The mean latency for N1 after direct stimulation was significantly longer than the mean latency for N1 in the 3 other groups (95% confidence intervals). There were no other significant differences in mean latencies among groups for any of the peaks.     

Computed tomography of masses of the brachial plexus and contributing nerve roots in dogs

A retrospective analysis of masses of the brachial plexus and contributing nerve roots in dogs seen at the University of Minnesota over a 17-year period was conducted. The goal of the study was to characterize their computed tomographic (CT) appearance and determine the minimum mass size confidently detectable. Twenty-four cases with a recorded diagnosis of brachial plexus or caudal cervical nerve root mass were found, wherein both the medical records and CT images were available for evaluation. These masses were characterized based on the presence or absence of contrast enhancement, margin character, size, extent of local invasion, and presence of vertebral canal or spinal cord involvement. Within the limits of this study, and the available histopathology, there appeared to be no clinically exploitable relationship between the tomographic appearance and the histologic interpretation. Twenty masses were noted to contrast enhance, typically with rim enhancement and a hypodense center. Only two dogs had a palpable axillary mass on physical examination. As measured, based on the largest dimension within a single slice, detectable masses ranged from 1.0 to 6.5 cm.     

Osteological features in pure-bred dogs predisposing to thoracic or lumbar spinal cord compression

Consistent with those vertebral sites most commonly clinically affected by spinal cord compression, body size normalised midsagittal diameters of the caudal vertebral foramen limits T10-T12 were significantly (P<0.05) lower in Dachshunds relative to other breeds. Minimal midsagittal diameters in Yorkshire Terriers and Maltese were noted at T11cd/12cr. However, these diameters were always larger (P<0.05) in small breeds compared to those in Dachshunds and large breeds suggesting that the small breeds investigated are at lower risk of developing clinical signs if a compressive disease occurs at that site. In large breeds, minimal values were present at L1cd/L2cr and in agreement with clinical findings correlate with those spinal sites most susceptible to spinal cord compression in nonchondrodystrophic large breeds. Caudal displacement of the lumbosacral enlargement of the spinal cord relative to the position previously noted in large breeds was confirmed for the Dachshunds and 50% of small breeds. However, caudal displacement was also noticed in the German Shepherd dogs.     

Use of vagal nerve stimulation as a treatment for refractory epilepsy in dogs

OBJECTIVE: To evaluate safety and efficacy of vagal nerve stimulation in dogs with refractory epilepsy. DESIGN: Placebo-controlled, double-masked, crossover study. ANIMALS: 10 dogs with poorly controlled seizures. PROCEDURE: A programmable pacemaker-like device designed to deliver intermittent stimulation to the left cervical trunk of the vagus was surgically implanted in each dog. Dogs were assigned randomly to two 13-week test periods, 1 with nerve stimulation and 1 without nerve stimulation. Owners recorded data on seizure frequency, duration, and intensity, as well as adverse effects. RESULTS: No significant difference in seizure frequency, duration, or severity was detected between overall 13-week treatment and control periods. During the final 4 weeks of the treatment period, a significant decrease in mean seizure frequency (34.4%) was detected, compared with the control period. Complications included transient bradycardia, asystole, and apnea during intraoperative device testing, and seroma formation, subcutaneous migration of the generator, and transient Horner's syndrome during the 14-day period between surgery and suture removal. No adverse effects of stimulation were detected, and most owners were satisfied with the treatment. CONCLUSIONS AND CLINICAL RELEVANCE: Vagal nerve stimulation is a potentially safe approach to seizure control that appears to be efficacious in certain dogs and should be considered a possible treatment option when antiepileptic medications are ineffective.     

Maturation of spinal-evoked potentials to tibial and ulnar nerve stimulation in clinically normal dogs

Spinal-evoked potentials were recorded from 2 litters of clinically normal mixed-breed dogs between 35 and 300 days of age. Summated responses to tibial nerve stimulation were recorded from percutaneous needle electrodes placed at L7-S1, L4-5, T13-L1, C7-T1, and the cisterna cerebellomedullaris. The ulnar nerve was stimulated with recordings at C7-T1 and the cisterna cerebellomedullaris. Amplitudes did not change significantly with age, but were significantly (P less than 0.05) different between various recording sites. On day 35, segmental and overall (L7-cisterna cerebellomedullaris) conduction velocities were less than half of the adult values. Spinal cord conduction velocities increased with age, reaching adult values at approximately 9 months of age. It was determined that quadratic equations best predicted the conduction velocities during maturation.     

A study of ultrasound-guided perineural injection of the caudal cervical spinal nerve roots in equine cadavers

ObjectivesTo develop an ultrasound-guided cervical perineural injection technique for horses and to evaluate and compare the distribution of contrast agent among perineural, intra-articular and periarticular injections.Study designProspective, experimental cadaveric study.AnimalsA total of 14 equine cadaveric necks.MethodsBilateral ultrasound-guided perineural injection technique for the caudal cervical spinal nerve roots (CSNRs 5–7) was developed. Paramagnetic or iodinated contrast was injected and the distribution of contrast was evaluated using magnetic resonance (MR) or computed tomography (CT) imaging, respectively. The presence of contrast in the CSNR region was determined by an observer unaware of the technique used for each injection performed. The ability of the perineural injection technique to distribute contrast agent to the CSNR region was compared with intra-articular and periarticular injection techniques.ResultsPerineural injection delivered contrast agent to the CSNR region 100% of the time and was significantly different when compared with intra-articular injection (p = 0.008). There was no difference in ability to deliver contrast agent to the CSNR region between the perineural and periarticular injection techniques or between the intra-articular and periarticular injection techniques.Conclusion and clinical relevanceThe ultrasound-guided perineural injection technique developed in this study accurately delivered contrast agent to the CSNR region in equine cadavers. This technique could potentially be used for the diagnosis and treatment of cervical pain in horses, particularly in cases where intra-articular cervical articular process joint injections have not been beneficial. Further studies are necessary to assess the effectiveness of the ultrasound-guided perineural injection technique in live horses.     

Combined Kirschner-Ehmer device and dorsal spinal plate fixation technique for caudal lumbar vertebral fractures in dogs

A new surgical technique was developed for the fixation of caudal lumbar vertebral fractures in dogs. The technique provides optimal stabilization, can be used in combination with dorsal decompression, and does not require an intact spinous process on the fractured vertebra or attachment of the fixation devices to the fractured vertebra. The fixation consists of a Kirschner-Ehmer device and dorsal spinal plates. After fracture healing, only mild sedation of the dog is needed to allow removal of the external hardware used in the fixation. The technique, its indications, and its use in 5 cases are described.     

Electromyography in the localization of spinal cord and nerve root neoplasia in dogs and cats.

In 8 cases (6 dogs and 2 cats) of spinal cord and nerve root neoplasia, electromyography was used to localize the area of involvement. The locations of the lesions were confirmed at necropsy.     

Combined Kirschner-Ehmer apparatus and dorsal spinal plate fixation of caudal lumbar fractures in dogs: biomechanical properties

The strength and rigidity of a new surgical technique for the stabilization of caudal lumbar fractures in dogs, using a Kirschner-Ehmer apparatus and a dorsal spinal plate (KE/DSP), were compared with 2 other methods of internal spinal fixation and with intact (control) spines, using a spinal test system that subjected the spines to 4-point bending. The fixation devices were applied to isolated canine lumbosacral spines (L1 to S3) from cadavers. A complete spinal separation was made in the spine implant specimens at L5-L6 by sharp dissection of all ligamentous structures connecting the two vertebrae. Bending moment vs L5-L6 angular deformation curves, and rigidity and load sustained at 10 degrees angular deformation (failure) were recorded for each fixation method and for the control spines. Values were compared by statistical analysis. The combined KE/DSP fixation and a combined vertebral body plate/dorsal spinal plate (VBP/DSP) fixation were stronger and more rigid than were the control spines and those fixed with a modified segmental-fixation method (P less than 0.05). There were no statistical differences in strength and rigidity between the 2 combined-fixation techniques. Although the VBP/DSP technique is not applicable to clinical caudal lumbar (L5-L6) fractures, it was compared in this study to the KE/DSP technique because a similar VBP/DSP technique was reported strongest in a similar study of L3-L4 simulated fractures, compared with 3 other spinal-fixation techniques that have been used in repair of caudal lumbar fractures. The technique has been used successfully in 6 dogs with caudal lumbar fractures.     

Electrical nerve stimulation as an aid to the placement of a brachial plexus block

Most local anaesthetic blocks are placed blindly, based on a sound knowledge of anatomy. Very often the relationship between the site of deposition of local anaesthetic and the nerve to be blocked is unknown. Large motor neurons may be stimulated with the aid of an electrical current. By observing for muscle twitches, through electrical stimulation of the nerve, a needle can be positioned extremely close to the nerve. The accuracy of local anaesthetic blocks can be improved by this technique. By using the lowest possible current a needle could be positioned with in 2-5 mm of a nerve. The correct duration of stimulation ensures that stimulation of sensory nerves does not occur The use of electrical nerve stimulation in veterinary medicine is a novel technique that requires further evaluation.     

An ultrastructural study of spinal nerve roots and dorsal root ganglia in aging rats with spontaneous radiculoneuropathy

The spinal nerve roots and dorsal ganglia of 104- to 135-week-old rats with spontaneous radiculoneuropathy were examined by light and electron microscopy. Demyelination was common in myelinated fibers of various diameters of both ventral and dorsal roots. The most striking alteration was wide distention of myelin sheaths, which extended throughout the entire internode. The spaces formed between separated lamellae frequently were invaded by macrophages. Subsequent vesicular degeneration of myelin seemed to be mediated by invading macrophages. These processes caused complete myelin destruction, but most axons showed no degenerative changes except for obvious reduction in diameter. Occasionally, there were clumping and partial degradation of neurofilaments and ruptured axolemma in the severely demyelinated axons. A few fibers also were undergoing wallerian-type degeneration, perhaps secondary to the severe demyelinative changes. Remyelinating fibers in various phases of repair were coexistent with markedly demyelinated ones. Demyelinative changes described above also developed within some of these remyelinated internodes. There were no remarkable changes in neurons of the dorsal root ganglia, though accumulation of lipofuscin was common. Our findings suggest that the changes in the nerve roots are essentially a primary segmental demyelination in aging rats with radiculoneuropathy.     

Somatosensory-evoked and spinal cord-evoked potentials in response to pudendal and tibial nerve stimulation in cats

Somatosensory-evoked potentials (SEP) and spinal cord-evoked potentials (SCEP) were recorded in clinically normal adult cats in response to electrical stimulation of pudendal and tibial nerves to provide normative data that can be used in a clinical evaluation of pudendal nerve function in cats after sacral or sacrococcygeal luxations or fractures. Responses to tibial nerve stimulation were included in the study as an internal control because it is usually not involved in these types of injuries and because its SEP and SCEP are easily recorded. Evoked potentials were characterized by the latencies (ms) of positive (P or p) and negative (N or n) peaks. The SEP resulting from percutaneous pudendal nerve stimulation consisted of a prominent P-N-P potential in the 30- to 80-ms range. The pudendal SCEP was not successfully recorded because of large muscle artifacts evoked from the sacral area. The tibial SEP was similar to the pudendal SEP, except that the prominent P-N-P series in the 35- to 81-ms range was preceded by a smaller p-n-p-n sequence in the 7- to 23-ms range. The tibial SCEP consisted of a P-N-P series in the 2- to 4-ms range.     

Diagnosis of spinal disease in dogs

Diagnosing spinal conditions in dogs requires an ability to conduct and interpret a neurological examination and a knowledge of ancillary diagnostic tests. This paper discusses the approach to the dog in which spinal disease is suspected, the performance of the neurological examination, and the diagnostic aids available. The differential diagnosis of various presenting syndromes is also considered.