Myotonic dystrophy-like disease in a dog

A mature female Rhodesian Ridgeback was determined to have a progressive, degenerative myopathy associated with myotonia, dysphagia, and marked muscle wasting. Clinical findings revealed a diffuse muscular disease with percussion dimpling, dysphagia, and creatine kinase elevation. A paroxysmal atrial tachycardia was found. Electromyography revealed a diffuse myopathy with high-frequency bizarre waves, myotonic discharges especially in the masticatory, laryngeal, and pharyngeal muscles. A few positive sharp waves were found in some of the appendicular muscles. Histopathologic and histochemical stains on skeletal muscle biopsy specimens demonstrated moderate fiber-size variation, myofiber architectural changes, muscle-fiber splitting, focal necrosis and phagocytosis, high percentage of internal nuclei, and atrophy of type-2 muscle fibers. A review of myotonic myopathies in the dog is presented. The clinical, electrophysiologic, and histochemical findings are similar to those for myotonic muscular dystrophy in man.     

Myokymia and neuromyotonia in a cat

A 6-year-old spayed female domestic shorthair cat was examined because of a 2-week history of rhythmic muscle movements. Physical examination revealed thoracic limb rigidity, contracture of the carpi, generalized muscle atrophy, and rhythmic rippling of the muscles of all 4 limbs. Results of a CBC and serum biochemistry profile were unremarkable other than high creatine kinase activity. Electromyography revealed unique high-frequency discharges, including rhythmic bursts of single motor unit potentials appearing as doublets (myokymia) and more prolonged bursts of nonrhythmic motor unit potentials with characteristic waning amplitudes (neuromyotonia). Histologic examination of muscle biopsy specimens revealed noninflammatory necrotizing myopathy with regeneration. The cat did not respond to treatment with carbamazepine or prednisone but improved rapidly after treatment with phenytoin was initiated. Six months after initial examination, electromyography revealed a substantial decrease in the amount of spontaneous activity in previously affected muscles. However, the myokymic and neuromyotonic discharges were still present, albeit with a substantial decrease in frequency.     

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.     

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)     

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.     

Myofiber expression of class I major histocompatibility complex accompanied by CD8+ T-cell-associated myofiber injury in a case of canine polymyositis

A 7-year-old female Labrador Retriever dog showed extreme muscular weakness, muscle wasting, dysbasia, and mild dysphagia. An elevated value of creatine kinase (335 IU/liter) in the serum was detected. Electromyographic findings included increased insertional activity, fibrillation potentials, and bizarre high-frequency repetitive potentials. Histopathologic examination of skeletal muscles revealed myofiber necrosis and phagocytosis, regeneration of myofibers, and perivascular, perimysial, and endomysial infiltrations of lymphocytes, macrophages and plasma cells. Immunohistochemical evaluation demonstrated that infiltrative cells in the early stage of myositis were CD8+ T-cells and that an increased expression of major histocompatibility complex (MHC) class I was apparent on the surface of nonnecrotic muscle fibers. In contrast, many CD3+ cells (T cells) and HLA-DR-positive macrophages and B lymphocytes were found in the severely affected areas. These results suggest that both expression of MHC class I and CD8+ T-cell infiltration may play an important role in initiation of myositis. These histopathologic findings resemble those reported in naturally occurring polymyositis in humans.     

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.     

Decrease in mass of slow and fast tenotomized muscles of guinea pigs: role of nerve impulses and neurogenic factors

The role of nerve impulses and neurogenic factors in the decrease in muscle mass following tenotomy was investigated in 30 adult (15 males, 15 females) guinea pigs. Unilateral tenotomy, neurectomy and simultaneous tenotomy and neurectomy of slow and fast hindlimb muscles were performed in 3 groups respectively. Each group comprised 10 guinea pigs. The unoperated hindlimb of each animal in each group served as control. The weight loss occurred in both slow and fast muscles but was greater in the slow soleus muscle as compared to the fast gastrocnemius muscle. In each muscle the weight loss was least in the tenotomized group. This was followed by the weight loss in the neurectomized group. The greatest weight loss was observed in the simultaneously tenotomized and neurectomized group. These observations agree with the suggestion of other workers that a possible neurogenic factor flowing from the nerves to the muscles was very significant in maintenance of muscle fibre stability. It indicated also that simultaneous neurectomy and tenotomy did not prevent degenerative changes in slow and fast muscles and that it was not nerve impulses reaching the tenotomized muscles that were responsible for degenerative changes observed but that other factors were responsible.     

Decrease in mass of slow and fast tenotomized muscles of guinea pigs: Role of nerve impulses and neurogenic factors

The role of nerve impulses and neurogenic factors in the decrease in muscle mass following tenotomy was investigated in 30 adult (15 males, 15 females) guinea pigs. Unilateral tenotomy, neurectomy and simultaneous tenotomy and neurectomy of slow and fast hindlimb muscles were performed in 3 groups respectively. Each group comprised 10 guinea pigs. The unoperated hindlimb of each animal in each group served as control. The weigyt loss occurred in both slow and fast muscles but was greater in the slow soleus muscle as compared to the fast gastrocnemius muscle. In each muscle the weight loss was least in the tenotomized group. This was followed by the weight loss in the neurectomized group. The greatest weight loss was observed in the simultaneously tenotomized and neurectomized group. These observations agree with the suggestion of other workers that a possible neurogenic factor flowing from the nerves to the muscles was very significant in maintenance of muscle fibre stability. It indicated also that simultaneous neurectomy and tenotomy did not prevent degenerative changes in slow and fast muscles and that it was not nerve impulses reaching the tenotomized muscles that were responsible for degenerative changes observed but that other factors were responsible.     

Juvenile-Onset Distal Myopathy in Rottweiler Dogs

Two juvenile Rottweiler siblings were presented with the complaint of decreased activity and various postural abnormalities, including plantigrade and palmigrade stance and splayed forepaw digits. The neurologic examinations were otherwise normal. Electromyography revealed rare fibrillation potentials and positive sharp waves. Motor nerve conduction velocities were normal, whereas compound muscle action potentials from the interosseous muscles were decreased. These findings were consistent with a primary myopathy. A 3rd pup from a different litter and a 4th pup from a litter with 3 of 8 affected dogs had similar clinical presentations. Histopathologic changes in fresh-frozen muscle biopsy samples were similar in all pups and consisted of myofiber atrophy with mild myonecrosis, endomysial fibrosis, and replacement of muscle with fatty tissue. These changes were more severe in distal muscles than in proximal muscles. Plasma carnitine concentrations (total and free) were decreased in all pups. Muscle carnitine concentrations (total and free) were decreased in 3 of 4 pups and the least affected pup had a borderline low free muscle carnitine concentration. Abnormalities involving major metabolic pathways were not found on quantification of organic and amino acids. Dystrophin immunocytochemistry was normal in 2 dogs tested. Distal myopathies in humans are classified under the dystrophic group of muscle disorders. These 4 cases represent a form of muscular dystrophy apparently not previously reported in dogs.     

Familial canine dermatomyositis: clinical, electrodiagnostic, and genetic studies

Three Collies with a skin disorder, 6 progeny from a breeding of 2 of the Collies (incross litter), and the 4 progeny from the breeding of an affected Collie male and a normal Labrador Retriever female (outcross litter) were examined. By 7 to 11 weeks of age, all 6 dogs in the incross litter developed a qualitatively similar, but variably severe, dermatitis of the ears, face, lips, tip of the tail, and over bony prominences of limbs. Later, myopathic signs characterized by bilaterally symmetrical skeletal muscle atrophy of the head, neck, trunk, and extremities; facial palsy; decreased jaw tone; stiff gait; and hyperreflexia were observed in the dogs more severely affected by the dermatitis. Of the 4 dogs in the outcross litter, 3 had similar, but milder, clinical manifestations of the dermatitis and myopathy. Cutaneous lesions consisted of intraepidermal and subepidermal vesicles or pustules with intradermal infiltration by leukocytes. Muscle lesions included myositis; myofiber degeneration, regeneration, and atrophy; and fibrosis. A generalized myopathy in the severely affected dogs was indicated by abnormal readings on needle electromyograms and normal motor nerve conduction velocities. Spontaneous needle electromyogram abnormalities were fibrillation potentials, positive sharp waves, and bizarre high-frequency discharges. Retrospective and prospective genetic analyses disclosed a definite familial tendency and indicated the condition has an autosomal dominant component.     

Electrically induced blink reflex and facial motor nerve stimulation in beagles

Electrophysiologic assessment of the blink reflex test and the muscle-evoked potentials evoked by stimulation of the facial nerve were performed in 15 healthy adult Beagles before and after supraorbital (trigeminal) and facial anesthetic nerve blocks performed by lidocaine injections. Unilateral electrical stimulation of the supraorbital nerve elicited 2 ipsilateral (R1 and R2) and a contralateral (Rc) reflex muscle potential in orbicularis oculi muscles. Electrical stimulation of the facial nerve elicited 2 muscle potentials (a direct response [D] and a reflex faciofacial response [RF]) in the ipsilateral orbicularis oculi muscle. Anesthetic block of the left supraorbital nerve resulted in bilateral lack of responses upon left supraorbital nerve stimulation, but normal responses in right and left orbicularis oculi muscles upon right supraorbital stimulation. Right facial anesthetic block produced lack of responses in the right orbicularis oculi muscle regardless the side of supraorbital nerve stimulation. Results of this study demonstrate that the blink reflex can be electrically elicited and assessed in dogs. Reference values for the blink reflex responses and for the muscle potentials evoked by direct facial nerve stimulation in dogs are provided. The potential usefulness of the electrically elicited blink reflex test in the diagnosis of peripheral facial and trigeminal dysfunction in dogs was demonstrated.     

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.     

Contributions of the glossopharyngeal nerve and the pharyngeal branch of the vagus nerve to the swallowing process in dogs

The separate contributions of the glossopharyngeal nerve and the pharyngeal branch of the vagus nerve to the innervation of the pharyngeal muscles were studied first in 10 canine cadavers by dissection of the pharyngeal plexus and the pharyngeal muscles. In 10 other dogs, the parent trunks and 1st division of the glossopharyngeal nerve and the pharyngeal branch of the vagus nerve were electrically stimulated. The evoked stimulation potentials were recorded from the stylopharyngeal, hyopharyngeal, thyropharyngeal, and cricopharyngeal muscles. One of the parent trunks was then transected, and the effects on the swallowing process were observed clinically and by contrast videofluorography. Denervation potentials resulting from nerve transection were recorded in the soft palate, the hyopharyngeal, thyropharyngeal, and cricopharyngeal muscles. The pharyngeal plexus was composed of branches originating from the glossopharyngeal nerve and the pharyngeal branch of the vagus nerve. In most dogs, the pharyngeal muscles and the soft palate were innervated ipsilaterally by both nerves. The swallowing process was more severely disturbed after bilateral transection of the pharyngeal branch of the vagus nerve than after bilateral transection of the glossopharyngeal nerve.     

Idiopathic Polyneuropathy in Alaskan Malamutes

Clinical and morphologic features of a progressive polyneuropathy in young mature Alaskan Malamutes are described. Clinical signs included progressive paraparesis, synchronous pelvic limb gait, exercise intolerance, hyperesthesia, hypore-flexia, muscle atrophy, and tetraplegia. Electromyographic testing revealed diffuse fibrillation potentials and positive sharp waves in limb muscles, especially in muscles below the elbow and stifle. Pathologic findings in skeletal muscles and peripheral nerves included neurogenic muscle atrophy, focal or diffuse loss of myelinated nerve fibers, myelinoaxonal necrosis, and variable demyelination or remyelination.
Ultrastructural changes included axonal degeneration, presence of numerous Büngner bands, and denervated Schwann cell subunits. The nature and distribution of abnormal electrophysiologic and pathologic findings were suggestive of a distal sensorimotor polyneuropathy, which we have termed idiopathic polyneuropathy of Alaskan Malamutes to distinguish this condition from hereditary polyneuropathy of Norwegian Alaskan Malamutes, last described in 1982.     

Evaluation of jitter by stimulated single-fiber electromyography in normal dogs

Single-fiber electromyography (SFEMG), a technique used to investigate neuromuscular transmission, has been described previously in the pelvic limb of dogs. Because preferential involvement of isolated muscle groups can occur in disorders of neuromuscular transmission, SFEMG was done in the peroneus longus (PL), extensor carpi radialis (ECR), and orbicularis oculi (OO) muscles of 10 adult, clinically normal dogs. Jitter was calculated as the mean absolute value of the consecutive differences in latency of 50 single muscle fiber action potentials after stimulation of intramuscular nerve bundles at the level of the motor point in at least 20 muscle fibers per muscle. Bilateral recordings were performed in 3 dogs. Mean jitter values were determined for each muscle, and differences among muscle groups and among dogs were compared. The upper limits of mean consecutive difference (mean plus 3 standard deviations) for the PL, ECR, and OO muscles were 21.94, 22.53, and 23.39 micros, respectively, and the upper limit of mean consecutive difference for individual muscle fibers in the respective fiber pools was 28.62, 36.39, and 35.68 micros. Jitter values for the ECR and OO were significantly higher than the jitter value for the PL muscle (P < .05). Significant differences among muscles or dogs or between sides were not observed for the ECR. Significant differences among dogs were observed for OO jitter values and were attributed to extremely low jitter values in 1 dog. Significant differences were demonstrated between sides for the PL and were attributed to small sample size. Results of this study provide normative data that can be used in the application of the stimulated SFEMG technique to dogs with suspected disorders of neuromuscular transmission.     

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.     

Electrically elicited blink reflex in horses with trigeminal and facial nerve blocks

OBJECTIVE: To reassess reference values for the components of the electrically induced blink reflex, document reference values for facial motor nerve conduction velocity, and demonstrate usefulness of the blink reflex as a diagnostic tool in peripheral facial and trigeminal nerve dysfunction in horses. ANIMALS: 10 healthy adult horses (8 males, 2 females) without neurologic abnormalities. PROCEDURE: Blink reflex tests were performed by electrical stimulation of the supraorbital nerve and facial (auriculopalpebral) nerve. Reflex and direct muscle-evoked potentials of the orbicularis oculi muscles were recorded from concentric needle electrodes inserted bilaterally in these muscles. Supraorbital and auriculopalpebral nerve blocks were performed by lidocaine hydrochloride injections. RESULTS: Supraorbital nerve stimulation elicited 2 or 3 ipsilateral and 1 contralateral reflex muscle potential in the orbicularis oculi muscles. Auriculopalpebral nerve stimulation elicited a direct and a reflex potential in the ipsilateral orbicularis oculi muscle. After left supraorbital nerve block, no responses could be elicited ipsilaterally or contralaterally upon stimulation of the blocked nerve, but bilateral responses were obtained upon stimulation of the right supraorbital nerve. After right auriculopalpebral nerve block, no responses were recorded from the right orbicularis oculi muscle upon stimulation of left or right supraorbital nerves. CONCLUSIONS AND CLINICAL RELEVANCE: Reference values for the components of the blink reflex and facial motor nerve conduction velocity will allow application of these tests to assist in the diagnosis of equine neurologic disorders involving the trigeminal and facial nerves, the brainstem, and the cranial end of the cervical segment of the spinal cord. This study reveals the usefulness of the blink reflex test in the diagnosis of peripheral trigeminal and facial nerve dysfunction in horses.     

Demonstration of the nerve distribution of the masticatory muscles in rabbits (Oryctolagus cuniculus)

Two methods can be used in order to demonstrate the nerve distribution of an organ. One is the three-dimensional reconstruction of the innervation pattern of the organ by tracing images of that organ from serial histological sections. The other is the in toto staining of the organ with subsequent clearing of the muscles. In the present study, in order to visualize the nerve distribution of the organ, that organ was completely cleared and the nerve fibres were stained. Detailed morphological structure of the intramuscular nerve distribution of a certain region and its functions are of importance not only for anatomists and physiologists but also for clinicians. In this study eight New Zealand rabbits were used to visualize the intramuscular nerve distribution of the muscles involved in mastication (temporalis m., pterygoideus medialis m., digastricus m., retractor mandibulae m. and masseter m.). The main nerve bundle was observed entering into the muscle as a single trunk and dividing into three branches in the muscle. These branches were also observed dividing into several subbranches while going to the periphery. When the samples were examined under a stereomicroscope, 'Y'-, 'I'- and 'O'-shaped communications between those branches were observed.     

Atrophic and regenerative changes in rabbit mimic muscles after lidocaine and bupivacaine application

Destruction and denervation atrophy in skeletal muscles caused by the injection of local anaesthetics was investigated by injecting lidocaine or bupivacaine around the rabbit facial nerve to produce facial paralysis. Animals were then sacrificed at 2, 4, 6, and 8 weeks post-injection, and changes in mimic muscle tissue were assessed at each stage by light microscopy and electron microscopy. Atrophic changes were observed at 2-6 weeks after injection, and regeneration started at 6-8 weeks. Compared to bupivacaine, lidocaine caused more dramatic atrophic changes and was associated with slower muscle regeneration.