Electromyographic evaluation of horses with laryngeal hemiplegia

Thirty-eight horses suspected of having laryngeal hemiplegia had electromyograms (EMGs) performed on the dorsal cricoarytenoid muscle (DCAM). Electromyographic abnormalities consisted of fibrillation potentials, positive sharp waves, bizarre high frequency discharges, and reduced insertional activity. Normal motor activity consisted of motor unit activity during inspiration, or less frequently motor unit activity during inspiration with subsequent tonic motor activity. In affected muscles, motor unit activity was often absent but when present there was activity consisting of motor units which did not correspond to a particular phase of respiration or it was consistent with normal motor unit activity.     

Electromyographic evaluation of adult Labrador retrievers with type-II muscle fiber deficiency

Labrador Retrievers with type-II muscle fiber deficiency were examined electrodiagnostically. Electromyographic changes consisted of positive sharp waves, fibrillation potentials, bizarre high-frequency discharges, and, rarely, myotonic-like discharges. Fasciculation potentials were recorded infrequently. Fibrillation potentials and bizarre high-frequency discharges were the most commonly observed electromyographic changes. Bizarre high-frequency discharges were prominent in muscles of the head and neck, proximal muscles of the thoracic limbs, and the thoracolumbar paraspinal musculature. Marked abnormalities were not observed in the motor nerve conduction velocity. Decremental responses of the evoked compound muscle action potential to repetitive nerve stimulation were not observed.     

Familial reflex myoclonus in Labrador Retrievers

Three 6-week-old male purebred yellow Labrador Retrievers were presented with intermittent stimulus-sensitive contractions of the appendicular and axial muscles. Five littermates were normal, although the grandsire of the affected litter had sired 2 previous litters containing similarly affected pup. Although alert and responsive, the affected dogs appeared decerebrate with extensor rigidity and opisthotonus during handling. During severe episodes, respiratory distress was observed. Generalized contractions were initiated by voluntary movements, but at rest the muscles relaxed. Neurologic deficits were not detected, although efforts to elicit segmental reflexes, assess muscle tone, or assist walking resulted in generalized stiffness. Electromyograms from the semitendinous muscles (musculi semitendinosus) had increased motor unit amplitude (up to 5,000 microV) with polyphasic action potentials. There were no myotonic discharges. A reduced interference pattern was seen. A single tactile stimuli of the distal limb resulted in 3 responses, each lasting less than or equal to 10 ms at latencies of 0 to 12 ms, 20 to 30 ms, and 35 to 40 ms, characteristic for reflex myoclonus. The motor nerve conduction velocities were normal for age (32 to 35 ms). Age-matched control dogs had motor unit action potentials of 100 to 200 microV and single compound motor unit discharges to single tactile stimuli. Therapeutic trials with diazepam and clonazepam produced minimal effects on the muscle contractions. Values of urinalyses, complete blood cell counts, and serum chemistries were within normal limits. Frozen muscle section biopsy findings, including enzyme histochemical assessment of muscle fiber types, were normal.(ABSTRACT TRUNCATED AT 250 WORDS)     

Myokymia and neuromyotonia in 37 Jack Russell terriers

The clinical and clinicopathological characteristics, treatment and outcome of vermicular muscle contractions (myokymia) and generalized muscle stiffness (neuromyotonia) in 37 Jack Russell terriers were evaluated retrospectively. Thirty dogs were affected by both disorders, whereas seven were presented with myokymia and never developed neuromyotonia. Clinical signs started at the mean age of 8 months. Except for signs of myokymia and neuromyotonia, clinical and neurological examination was normal in all dogs. Thirty dogs demonstrated typical signs of hereditary ataxia.Changes in serum chemistry included increased creatine kinase, aspartate aminotransferase and alanine aminotransferase concentrations. Electromyographic abnormalities, especially in muscles showing macroscopically visible myokymia, consisted of semirhythmic bursts of doublet, triplet, or multiplet discharges of a single motor unit. The amplitudes varied between 80 μV and 1 mV and occurred with an interburst frequency between 10 and 40 Hz and an intraburst frequency between 150 and 280 Hz.Most dogs were treated with a sodium channel blocker with variable results. Seven dogs died (most likely because of hyperthermia) or were euthanased during a neuromyotonic attack; 15 dogs were euthanased due to worsening of clinical signs, or lack of or no long-lasting effect of medication, and three were euthanased for unknown or unrelated reasons. Nine dogs were lost to follow-up and three were still alive 5–10.5 years after the start of clinical signs. In conclusion, young Jack Russell terriers with myokymia and neuromyotonia should undergo a complete blood and electrophysiological examination. Long-term prognosis is not favourable.     

Use of electromyography for the diagnosis of equine hyperkalemic periodic paresis.

The use of electromyography (EMG) as a diagnostic aid for equine hyperkalemic periodic paresis (EHPP) was investigated in seven affected and seven control horses. Affected horses were confirmed positive for EHPP either by elevated serum potassium concentration with clinical signs of myotonia, or by inducing hyperkalemia and clinical signs using oral potassium chloride challenge. All horses were asymptomatic at the time EMG was performed, using bipolar fine wire needle electrodes. The myopotentials were recorded on magnetic tape and displayed on paper charts for analysis. Insertional and resting activity were recorded from the right supraspinatus, triceps, extensor carpi radialis and gluteal muscles in standing horses. Myotonic discharges were seen in six of seven affected horses but not in any of the controls. All seven affected horses and two control horses had prolonged insertional activity. Five out of seven affected horses and one control horse displayed spontaneous motor unit discharges unrelated to recording electrode movement. Myoelectrical potentials containing closely timed muscle potentials, i.e. doublets, were found in all affected horses, with four of seven affected horses also showing triplets. These potentials were not observed in any of the controls. No obvious difference in activity was observed among the four muscle sites tested. It is concluded that EMG is a safe and useful tool for diagnosing EHPP in horses not currently displaying clinical signs. Myotonic discharges and doublets appear to be the most diagnostically significant electromyographic abnormalities in EHPP affected horses.     

Electromyographic changes of motor unit activity in horses with induced hypocalcemia and hypomagnesemia

OBJECTIVE: To determine whether electromyographic abnormalities are evident in skeletal muscles in horses with induced hypocalcemia and hypomagnesemia. ANIMALS: 7 healthy adult Dutch Warmblood horses. PROCEDURES: Electromyographic examination was performed in the lateral vastus, triceps, and subclavian muscles before and after IV infusion of EDTA. An initial dose (mean +/- SD, 564+/-48 ml) of a 10% solution of sodium EDTA was administered IV during a period of 21+/-73 minutes to establish a blood concentration of ionized calcium of approximately 0.5 mmol/L. Average rate of EDTA infusion to maintain ionized calcium at this concentration was 6.6 ml/min. RESULTS: Mean blood concentrations of ionized calcium and magnesium were 1.39+/-0.06 and 0.84+/-0.09 mM, respectively before EDTA infusion; after EDTA infusion, concentrations were 0.48+/-0.05 and 0.44+/-0.20 mM, respectively. This state induced positive waves; fibrillation potentials; doublets, triplets, and multiplets; complex repetitive discharges; and neuromyotonia. Analysis of motor unit action potentials (MUAP) after EDTA infusion revealed an increase in prevalence of polyphasic and complex MUAP in all muscles. CONCLUSIONS AND CLINICAL RELEVANCE: None of the horses had classical signs of hypocalcemia and hypomagnesemia. In contrast, all horses had spontaneous activity in the measured muscles indicative of nerve hyperirritability. Calcium and magnesium deficits appear to have consequences, which may be subclinical, affecting functions of the neuromuscular system. This is of interest for equestrian sports in which hypocalcemia and hypomagnesemia are expected, such as during endurance rides.     

Presumed localized tetanus in two cats

In this report two cases of localised tetanus in two young (<1 year) intact male and outdoor DSH cats, which had been missing, are described. Clinical examination revealed severe muscular spasms on the right (case 1) or both thoracic limbs (case 2). In the latter cat, wrinkling of the forehead and mild trismus were also seen. The routine diagnostic workup (CBC, survey radiographs of the spine, CSF analysis) did not reveal any abnormalities in both cats. EMG testing on the affected muscles in the second animal showed persistent spontaneous motor unit potentials, strongly indicating tetanus. The treatment, that was symptomatic (diazepam, metronidazole) and supportive (physical therapy, assist feeding and intravenous fluid therapy) resulted in the progressive improvement of limb rigidity and the restoration of motor dysfunction in a period of 5- (case 1) and 2- (case 2) month duration.     

Electrodiagnostic evaluation in feline hypertrophic muscular dystrophy

Standard needle electromyography (EMG) of 56 muscles and nerve conduction velocities (NCV) of the ulnar and common peroneal nerves were investigated in each of six cats affected with hypertrophic feline muscular dystrophy, 10 related heterozygote carriers and 10 normal cats. The EMG findings were considered normal in carrier and control cats, and consisted of 33% normal readings, 22% myotonic discharges, 18% fibrillation potentials, 11% prolonged insertional potentials, 10% complex repetitive discharges and 6% positive sharp waves in affected cats. Muscles of the proximal limbs were most frequently affected. No differences in NCV were found between the three cat groups. It was concluded that dystrophin-deficient dystrophic cats have widespread and frequent EMG changes, predominantly myotonic discharges and fibrillation potentials, which are most pronounced in the proximal appendicular muscles.     

Prednisolone-responsive neuropathy in a cat

Chronic relapsing polyneuropathy was diagnosed in a 15-month-old cat with a 12-week history of limb weakness. The clinical course was punctuated by spontaneous remissions and relapse. There were two striking physical findings, weak withdrawal reflexes and atrophy of the proximal and distal limb muscles. Electrophysiological findings typical of a demyelinating motor neuropathy were present, namely small, dispersed compound muscle action potentials, markedly slow motor conduction and denervation potentials that were more prominent dis-tally. Muscle biopsies showed changes consistent with denervation and a paucity of myelinated axons in intramuscular nerve bundles. The neuropathy responded rapidly and completely to prednisolone administration, which was slowly tapered over several months.     

Dystrophin‐deficient muscular dystrophy in a Norfolk terrier

A six‐month‐old male entire Norfolk terrier was presented with a 3‐month history of poor development, reluctance to exercise and progressive and diffuse muscle atrophy. Serum creatine kinase concentration was markedly elevated. Magnetic resonance imaging of the epaxial muscles revealed asymmetrical streaky signal changes aligned within the muscle fibres (hyperintense on T2‐weighted images and short‐tau inversion recovery with moderate contrast enhancement on T1‐weighted images). Electromyography revealed pseudomyotonic discharges and fibrillation potentials localised at the level of the supraspinatus, epaxial muscles and tibial cranialis muscles. Muscle biopsy results were consistent with dystrophin‐deficient muscular dystrophy. The dog remained stable 7 months after diagnosis with coenzyme Q10 and l ‐carnitine; however after that time, there was a marked deterioration and the owners elected euthanasia. This case report describes the clinical presentation, magnetic resonance imaging, electrodiagnostic and histopathological findings with immunohistochemical analysis in a Norfolk terrier with confirmed dystrophin‐deficient muscular dystrophy, which has not been previously described in this breed.     

Multiple myeloma with associated polyneuropathy in a German shepherd dog

A 12-year-old female, neutered German shepherd dog developed progressive hindlimb followed by forelimb ataxia leading to tetraplegia. Neurological examination suggested lower motor dysfunction. Biochemical evaluation revealed a monoclonal hypergammaglobulinaemia, hypoalbuminaemia and hypercalcaemia. Multiple lytic lesions were identified radiographically in numerous bones. A bone marrow aspirate confirmed the diagnosis of multiple myeloma, with large numbers of plasma cells seen in clusters. An electromyogram revealed positive sharp waves and fibrillation potentials in the skeletal muscles of the limbs, suggesting a polyneuropathy. The dog was treated with chemotherapy using melphalan and prednisolone. Both the hypergammaglobulinaemia and the polyneuropathy resolved and the dog had normal motor function four weeks after commencing treatment. Polyneuropathy may occur as a paraneoplastic syndrome secondary to myeloma, and in this case was reversible following treatment of the underlying disease.     

Cutaneous saphenous nerve graft for the treatment of sciatic neurotmesis in a dog

CASE DESCRIPTION: A 2-year-old Griffon Vendéen was examined because of a 1-month history of right hind limb lameness after a traumatic injury. CLINICAL FINDINGS: Neurologic examination revealed monoplegia and anesthesia of the right hind limb distal to the stifle (femorotibial) joint except for the area supplied by the cutaneous saphenous nerve. Results of electromyographic testing were consistent with a severe lesion of the tibial and peroneal nerves at the level of the stifle joint. TREATMENT AND OUTCOME: Exploratory surgery revealed an 80-mm-long gap in both the peroneal and tibial branches of the right sciatic nerve. A section of the left cutaneous saphenous nerve was interposed to graft the nerve defects. The dog received joint mechanotherapy and electrophysiologic therapy during the reinnervation process. Ten months after surgery, the dog had recovered almost completely. Neurologic examination revealed diminished flexion of the tarsal and digital joints. Repeat electromyographic testing revealed no abnormal spontaneous electrical activity in the right hind limb musculature, and small compound muscle action potentials were recorded in the right interosseous and cranial tibial muscles. CLINICAL RELEVANCE: Without surgical treatment, neurotmesis injury results in poor recovery of motor and sensory functions and may result in amputation. If a nerve defect exists, nerve grafting should be considered, even if the procedure is delayed until well after the injury. The sensory portion of the cutaneous saphenous nerve is a potential source of peripheral nerve for grafting in dogs. Reinnervation is a long-term process and physiologic support and owner involvement are necessary, but nearly complete functional recovery is possible.     

Neuromyotonia in a horse

This article describes the clinical and electromyographic findings of neuromyotonia in a 19‐month‐old male crossbred Quarter Horse that presented with stiffness and muscle asymmetry in the hind limbs as well as sacrococcygeal, paravertebral, and gluteal myokymia. An electromyographic study showed spontaneous continuous muscle fiber activity with high‐frequency discharges, fibrillations, positive sharp waves, fasciculation potentials, and complex repetitive discharges. Histological examination of the gluteal muscle showed a mixed neurogenic and myopathic pattern. The findings are consistent with neuromyotonia.     

Idiopathic polyradiculoneuropathy in a Bengal cat: electrophysiological findings and 1 year follow-up

This report describes a rapidly progressive loss of motor function in a 16-month-old male neutered Bengal cat, beginning in the pelvic limbs and progressing to involve all limbs and rendering the cat non-ambulatory. The neurological examination revealed flaccid tetraparesis with decreased spinal reflexes but preserved conscious proprioception and skin sensation. Extensive electrophysiological tests were conducted including electromyography, motor and sensory peripheral nerves potential recordings and 'late' potentials, defining the electrodiagnostic characteristics of this disease. Based on the electrophysiological findings, a generalised proximal and predominantly axonal neuropathy affecting the ventral (motor) nerve roots was suspected. As no aetiology was identified, this disease was classified as idiopathic polyradiculoneuropathy. Over a year, the cat presented three separate episodes of tetraparesis, each with a spontaneous complete recovery, consistent with the reportedly good prognosis for this disease.     

Gender differences in the morphometric properties of muscle fibres and the innervation ratio of motor units in rat medial gastrocnemius muscle

With 2 figures and 2 tables SUMMARY: Previous studies of motor unit contractile properties in the rat medial gastrocnemius revealed that these units generate higher forces in males than in females. Therefore, in the present study the number and morphometric parameters of muscle fibres and the innervation ratio of motor units in the medial gastrocnemius muscle were studied in male and female Wistar rats. The study additionally aimed at determining reasons of gender differences in motor unit force parameters, i.e. the number and diameter of muscle fibres, and mean values of the motor unit innervation ratios. Following staining of reticuline fibres by silver impregnation, the number, diameter and cross-section area of muscle fibres were determined on microscopic images of transverse muscle sections. In males, the muscles were approximately 1.5 times larger by mass and contained about 11 800 muscle fibres, whereas in females the muscles contained around 8000 fibres. In addition, the mean diameter and mean cross-section area of muscle fibres were 14 and 29% larger in males, respectively. Based on previously determined numbers of motoneurons innervating the medial gastrocnemius muscle in male and female rats, the mean innervation ratio, i.e. the number of muscle fibres innervated by one motoneuron, was estimated. This ratio was approximately 26% greater in males compared to females, with values of 207 and 153 fibres per motoneuron, respectively. Therefore, the differences in muscle fibre morphometric parameters and in the innervation ratio are responsible for higher forces of motor units in male muscles.     

Tetanus in cats: 3 case descriptions

Three cats with spasticity on one leg or on all four limbs were presented between 1996 and 1998 at the Department of clinical veterinary medicine, Section of neurology, Vetsuisse-Faculty of Bern. The presumptive diagnosis was tetanus. A focal form was present in two cases and generalised tetanus in one cat. All cats had a history of injury at the affected legs respectively at the neck. The first clinical signs were seen between two days and three weeks after injury. The bacteriologic examination of serous fluid from the site of injury revealed an infection with Clostridium. EMG in one cat during anaesthesia showed motor united potentials (MUPs) on the spastic leg. All patients received antibiotics (Penicillin, respectively Amoxicillin/Clavulanic acid and Metronidazol). Supportive aid were initially sedation, wound revision and in one cat nutrition through oesophageal sonde. In a second phase physiotherapy was performed. All three animals were significantly better after a couple of weeks, two cats were without symptoms after eight and five weeks respectively.     

Motor unit irritability in Beagles Before and after exposure to cholinesterase inhibitors.

Electromyographic (EMG) examinations were performed on Beagles before and for 7 days after oral administration of one of the following organophosphate (OP) compounds; ronnel (55.0 or 110.0 mg/kg), dichlorvos (29.7, 59.4, or 148.5 mg/kg), or cythioate (24.8 or 33.0 mg/kg). The EMG values determined were evoked potentials, after-discharge activity, F-wave activity, nerve conduction velocity, and motor unit potential activity associated with interosseous and pectineal reflexes. Erythrocyte cholinesterase (ChE) activities were measured in some dogs. Ronnel did not have an effect on ChE activity, whereas dichlorvos and cythioate, at all dosage levels, had an inhibitory effect. Some dogs had minor signs of OP toxicosis. The EMG changes for individual OP compounds were not statistically significant (P greater than 0.05), but pooled results revealed an increased duration of evoked potentials, increased after-discharge activity, and decreased F-wave activity; however, only the effect on duration was significant (P less than 0.05). Reflex motor unit potential activity and nerve conduction velocities were not affected. Effects of neostigmine (0.1 to 0.4 mg/kg) given IV to anesthetized, atropinized Beagles were similar to those effects shown by pooled data for the OP compounds, but considerably more muscle fasciculation was produced. Results of this study indicate that even when erythrocyte ChE activity is reduced by OP compounds at dosage levels that produce no or minimal visible signs of toxicosis, EMG reveals little evidence for increased motor unit irritability.     

Motor Fibers in the Canine Distal Caudal Cutaneous Sural Nerve—Dual Innervation of the Hind Limb Plantar Muscles

The function of the communicating branch of the distal caudal cutaneous sural (DCCS) nerve to the tibial nerve was investigated in 7 adult dogs and was found to contain the motor component of this nerve. This function was studied by direct visualization of the contraction of the hind limb plantar muscles and by direct electrophysiologic recording of motor unit action potentials in these muscles, following stimulation of the DCCS nerve. Contraction of all of the mm. interossei, the mm. lumbricales, the m. adductor digiti quinti and the m. adductor digiti secundi was observed with the stimulation of either the tibial or the DCCS nerves, although there was a qualitative variability in the plantar muscles exhibiting the strongest contraction with stimulation of the latter nerve. This communicating branch was not found in one of the experimental dogs, suggesting some individual variability in the DCCS nerve anatomy and subsequent function. This study conclusively demonstrated that the canine DCCS nerve contains both motor and sensory nerve fibers, which is similar to this nerve in the rat, but anatomically and functionally different to that in the human and the cat.     

Quantitative analysis of motor unit action potentials in the subclavian muscle of healthy horses

OBJECTIVE: To evaluate the application of analysis of motor unit action potentials (MUAP) in horses and to obtain values of MUAP for the subclavian muscle of horses. ANIMALS: 10 healthy adult Dutch Warmblood horses. PROCEDURE: Electromyographic examination of the subclavian muscle in conscious nonsedated horses was performed to evaluate insertional activity, spontaneous activity, MUAP variables, and recruitment patterns. Muscle and body temperatures were measured at the beginning and end of the procedure. Amplitude, duration, number of phases, and number of changes in direction (ie, turns) for all representative MUAP were analyzed to determine values for this muscle in this group of horses. RESULTS: Mean +/- SD duration of insertional activity was 471.7 +/- 33.45 milliseconds. Mean MUAP amplitude in the examined horses was 379 RV (95% confidence interval [CI], 349 to 410 microV). Mean MUAP duration of the subclavian muscle was 727 milliseconds (95% CI, 6.84 to 7.71 milliseconds). Mean number of phases was 2.9, and mean number of turns was 3.0. Prevalence of polyphasic MUAP defined as MUAP with > 4 phases, was 77%. Number of MUAP that had > 5 turns was 2.4%. Satellite potentials were found in 1.0% of the MUAP CONCLUSIONS AND CLINICAL RELEVANCE: This study revealed that electromyography including MUAP analysis can be performed in horses, and values for the subclavian muscle in healthy adult horses can be obtained. Analysis of MUAP could be a valuable diagnostic tool for use in discriminating between myogenic and neurogenic problems in horses.