Tiny reviews – JVIM Nov/Dec 2017

by Deena Tiches, DVM, DACVIM (Neurology)
Originally posted 2018-03-15 on the NeuroWebVet website; modified and reprinted with permission.

This edition of tiny neuro reviews covers neurology articles published in the Nov/Dec 2017 issue of Journal of Veterinary Internal Medicine


CM/SM & cranial cervical junction abnormalities

Researchers and veterinarians at the Veterinary Teaching Hospital of University of Helsinki described Chiari-like malformation (CM), syringomyelia (SM), and cranial cervical junction (CCJ) abnormalities in Chihuahuas. Fifty-three client-owned Chihuahuas were examined prospectively. Scratching was the most common CM/SM-related clinical sign (73%) and decreased postural reaction the most common neurologic deficit (87%). CM (100%) and SM (38%) was detected in these dogs. Syringomyelia was associated with the presence of CM/SM-related clinical signs (P = 0.034), and medullary kinking and sum indices were higher in dogs with clinical signs (P = 0.016 and P = 0.007, respectively). They concluded that syringomyelia and CCJ abnormalities are prevalent in Chihuahuas. Syringomyelia was an important factor for the presence of CM/SM-related clinical signs, but many dogs suffered from similar clinical signs without being affected by SM, highlighting the clinical importance of CCJ abnormalities in Chihuahuas. Download article

Progressive myelomalacia in IVDE

The onset and progression of clinical signs of progressive myelomalacia (PMM) in a large case cohort of dogs were completed at North Carolina State University College of Veterinary Medicine. Fifty-one dogs with either a histopathologic diagnosis or high clinical suspicion of PMM due to intervertebral disk extrusion were selected by a medical records search. Approximately half of the dogs were dachshunds. A total of 56 disc extrusions were reported (5 dogs had 2 sites involved). Around 20% of the disk extrusions were located at T12-T13 and 33% were mid-to-caudal lumbar discs (between L3 and L6). More than half of the dogs (30 of 51) had systemic abnormalities documented. These included hypothermia (ie, rectal temperature lower than 99°F) in 29% of the dogs, fever (ie, rectal temperature higher than 102.5°F) in 14%, and diffuse hyperesthesia (ie, not localized to the spine) in 18%. The majority of dogs developed PMM within 2 days of presentation and was euthanized within the next 3 days. However, onset can be delayed up to 5 days after presentation and progression to euthanasia taking as long as 2 weeks. Mid-to-caudal lumbar discs might be associated with an increased risk of PMM. Download article

Bacteriuria in chronically paralyzed dogs

Paralysis is a known risk factor for urinary tract infections (UTI), sepsis, and death in paralyzed people, but there are no data available on diagnostic criteria for UTI versus bacteriuria, their frequency, or clinical implications in chronically paralyzed dogs. A retrospective, observational study was conducted at the College of Veterinary Medicine, North Carolina State University to determine the frequency of bacteriuria, associated clinical signs, and survival rate in chronically paralyzed dogs. Medical records of dogs meeting inclusion criteria were reviewed for results of urine culture (UC), urinalysis, and clinical signs. Outcome was compared between dogs with and without bacteriuria. Thirty-five of 47 dogs had at least 1 positive UC, and 13 had recurrent bacteriuria. Fever was present at time of UC in 5 of 68 observations, 2 with and 3 without bacteriuria. Pyuria was significantly associated with positive cultures (P < 0.001), but cloudiness was not (P = 0.076). Survival data in 35 dogs (8 dead) showed no association between bacteriuria and survival (P = 0.69). Bacteriuria is common in paralyzed dogs but does not cause fever, therefore the diagnostic criteria of UTI are unclear. They did not detect an association of bacteriuria with survival, but this needs further confirmation. Download article

Phenobarbital-induced pseudolymphoma

Canada West Veterinary Specialists submitted a case report of suspected phenobarbital-induced pseudolymphoma in a dog. Pseudolymphoma is a drug reaction to anticonvulsant medications that is well recognized in humans. Until now, it has been reported in one cat but no dogs. In this report, lymphoma-like clinical signs were suspected to be secondary to phenobarbital administration in a dog. A 2.5-year-old male, neutered shepherd mix presented with a 3-day history of progressive ataxia, dazed mentation, pyrexia, and lethargy. The dog developed generalized lymphadenopathy and sustained pyrexia during hospitalization. Current medications were levetiracetam and phenobarbital for epilepsy. Serum concentrations of both were within standard therapeutic ranges. Abdominal ultrasound revealed hepatomegaly, splenomegaly, and generalized lymphadenopathy. Cytology of the peripheral lymph nodes was consistent with reactive lymph nodes, and aspirates of the liver and spleen revealed histiocytic-neutrophilic inflammation. Phenobarbital was discontinued and replaced with zonisamide. Within 24 hours, the dog was normothermic, and other clinical signs resolved within a week. This case highlights a potentially serious, yet reversible, adverse reaction to phenobarbital in a dog. This idiosyncratic reaction could be mistaken for neoplasia and is an important differential for lymphoma-like signs in any dog administered phenobarbital. Download article

Tiny reviews – JVIM Jan/Feb 2018

by Deena Tiches, DVM, DACVIM (Neurology)
Originally posted on the NeuroWebVet website; modified and reprinted with permission.

Whoa! Lots to cover here! Neuro topics from the last 2 months of JVIM include:

Epidural response to IVD extrusion

Although the basic pathophysiology is the same in both cervical and thoracolumbar intervertebral disk (IVD) extrusions, researchers at the University of Bern evaluated the differences in epidural inflammatory response between the two. Clinical data and histopathologic variables were investigated. Associations between severity of epidural inflammation and clinical and pathologic variables, impact of chondrodystrophic phenotype, and localization (cervical versus thoracolumbar) were evaluated statistically. Dogs with cervical IVD extrusion were significantly older, had less severe and longer duration of neurologic signs, were more painful, and had a better outcome than dogs with a thoracolumbar IVD extrusion. On histopathology, cervical epidural material had less severe calcification and inflammation. No significant differences regarding chondrodystrophic phenotype were found. Comparing the extent of the inflammatory response, dogs with cervical IVD extrusion displayed significantly less intense inflammation than those with thoracolumbar IVD extrusion. The larger cervical epidural space may limit tissue injury and chemical irritation by the extruded nucleus pulposus (NP) within the vertebral canal, consequently provoking less inflammatory reaction. Notably, there was a significantly less severe epidural inflammatory response in the former, indicating a response of the innate immune system. This finding correlated positively with significantly less NP calcification in cervical extrusions indicating biochemical, metabolic, and biomechanical differences between the 2 locations, which remain to be characterized in future studies. Download article

Intracranial hypertension

Intracranial hypertension is defined as a continuous increase in intracranial pressure above the reference range. It can be caused by various intracranial diseases (eg, trauma, hemorrhage, infarction, ischemia, edema, masses, encephalopathy, status epilepticus). Intracranial hypertension can cause lethal damage to the brain as a result of decreased cerebral blood flow and mechanical compression of brain structures. Therefore, rapid diagnosis and appropriate treatment of intracranial hypertension are important. Transcranial Doppler ultrasound examination (TCD) is a rapid, noninvasive technique used to evaluate cerebral blood flow and is useful for the detection of intracranial hypertension in humans. Investigators at The Veterinary Teaching Hospital, Graduate School of Veterinary Medicine, Hokkaido University evaluated the association between the TCD variables and intracranial hypertension in dogs with intracranial diseases. Fifty-one client owned dogs with neurologic disease were studied. Dogs were classified into 3 groups based on MRI findings: no structural diseases (group I), structural disease without MRI evidence of intracranial hypertension (group II), and structural disease with MRI evidence of intracranial hypertension (group III). The TCD vascular resistance variables (resistive index [RI], pulsatility index [PI], and the ratio of systolic to diastolic mean velocity [Sm/Dm]) were measured. Fifteen, 22, and 13 dogs were classified into groups I, II, and III, respectively. Dogs in group III had significantly higher Sm/Dm (median, 1.78; range, 1.44-2.58) than those in group I (median, 1.63; range, 1.43-1.75) and group II (median, 1.62; range, 1.27-2.10). No significant differences in RI and PI were identified among groups. Our findings suggest that increased Sm/Dm is associated with MRI findings of suspected intracranial hypertension in dogs with intracranial diseases and that TCD could be a useful tool to help to diagnose intracranial hypertension. Download article

Meningoencephalomyelitis of unknown origin (MUO)

Meningoencephalomyelitis of unknown origin (MUO) is a common and life-threatening neuroinflammatory disease in dogs. Features of the disease are suggestive of an underlying immune-mediated process, but the association of this disease with a pathogen is still unknown. Colorado State University with collaboration between the Department of Microbiology, Immunology and Pathology and the Department of Clinical Sciences searched for a candidate etiologic agent associated with cases of MUO using next generation metagenomic sequencing. In metagenomic sequencing, total nucleic acids from a clinical or environmental sample are randomly sequenced and are taxonomically categorized by comparison to known sequences in public databases. They evaluated twenty-two dogs diagnosed with either MUO (11/22; 10 CSF and 3 brain), or noninflammatory CNS diseases inconsistent with MUO (11/22; 11 CSF and 2 brain) that served as negative controls. Fresh-frozen cerebrospinal fluid (CSF; 21) and brain (5) samples were collected and RNA and DNA were extracted separately for shotgun metagenomic sequencing. No candidate etiologic agents were identified in dogs with MUO. These results support, but do not prove, the hypothesis that MUO is not associated with infectious agents and might be an autoimmune disease. Download article

Chiari malformation syringomyelia

Characterizing the signs of CMSM (Chiari malformation syringomyelia) in Cavalier King Charles spaniels (CKCS) is challenging because of the difficulty of inferring signs of pain from behavior in dogs. It is crucial to have quantitative measures of chronic pain that are valid and reliable in clinical patients to enable development and testing of interventions (such as drugs or surgical procedures) designed to decrease such pain. Veterinarians at NCSU designed a study to develop a tool to capture owner-reported clinical signs for use in clinical trials and to examine the relationship among owner-reported signs, presence of pain on neurologic examination, and presence and severity of SM (syringomyelia) on MRI. They hypothesized that owner-reported signs would correlate moderately or highly with MRI findings. Fifty dogs were enrolled in the study. SM was present in 30 of 50 dogs, and lateralization of SM was present in 15 dogs. All dogs affected had SM located in the cervical spinal cord, and 24 also had SM in the cranial thoracic spinal cord. There was no relationship between the presence of owner-reported pain (yes or no) or scratching (yes or no) and the presence of SM. Likewise, the total scratch score and pain score were not significantly associated with the presence of SM. In conclusion, the full range of signs reported by owners of CKCS includes a variety of manifestations of pain, with phantom scratching as the most commonly reported sign followed by crying out when being lifted. Download article


GM2-gangliosidosis is a fatal neurodegenerative lysosomal storage disease (LSD) caused by deficiency of either β-hexosaminidase A (Hex-A) and β-hexosaminidase B (Hex-B) together, or the GM2 activator protein. Clinical signs can be variable and are not pathognomonic for the specific, causal deficiency. Researchers at the University of Pennsylvania School of Veterinary Medicine sought to characterize the phenotype and genotype of GM2-gangliosidosis disease in an affected dog. A 14-month-old, female Shiba Inu presented with clinical signs resembling GM2-gangliosidosis in humans and GM1-gangliosidosis in the Shiba Inu. Magnetic resonance imaging (MRI) of the dog’s brain indicated neurodegenerative disease, and evaluation of cerebrospinal fluid (CSF) identified storage granules in leukocytes. Lysosomal enzyme assays of plasma and leukocytes showed deficiencies of Hex-A and Hex-B activities in both tissues. Genetic analysis identified a homozygous, 3-base pair deletion in the HEXB gene (c.618-620delCCT). Clinical, biochemical, and molecular features were characterized in a Shiba Inu with GM2-gangliosidosis. The deletion of 3 adjacent base pairs in HEXB predicts the loss of a leucine residue at amino acid position 207 (p.Leu207del) supporting the hypothesis that GM2-gangliosidosis seen in this dog is the Sandhoff type. Because GM1-gangliosidosis also exists in this breed with almost identical clinical signs, genetic testing for both GM1- and GM2-gangliosidosis should be considered to make a definitive diagnosis. Download article

Extended-release levetiracetam in cats

Repeated PO dosing of anti-epileptic drugs may contribute to poor compliance in treated cats. Intermediate-release levetiracetam has been used safely in cats, but must be given q8h to maintain serum concentrations in the therapeutic interval for humans (5-45 μg/mL). Approved extended-release levetiracetam (XRL) for human use may require less frequent dosing, but the large dosing unit has limited its use in cats. Researchers at the University of Wisconsin and Auburn University hypothesized that, in healthy cats, serum levetiracetam concentration will remain above 5 μg/mL for at least 24 hours after administration of a single dose of 500 mg XRL PO and will be well tolerated. They found that the median dosage of 86.2 mg/kg, (range, 80-94.3) achieved a mean maximum concentration (Cmax) of 89.8 ± 25.8 μg/mL at 4.9 ±1.57 hours. Serum levetiracetam was >5 μg/mL in all cats by 90 minutes. Mean concentrations were 43.7 ± 18.4 and 4.9 ± 3.4 μg/mL at 12 and 24 hours, respectively. The half-life was 4.1 ± 1.0 hours. The drug was well tolerated. They concluded that a single 500 mg PO dose of XRL safely maintained serum levetiracetam concentration ≥5 μg/mL in healthy cats for at least 21 hours. Clinical efficacy studies in epileptic cats receiving XRL are indicated; however, monitoring should be implemented for individual cats. Download article

Acute polyradiculoneuritis

Acute polyradiculoneuritis (APN) is an immune-mediated peripheral nerve disorder in dogs that shares many similarities with Guillain-Barré syndrome (GBS) in humans, in which the bacterial pathogen Campylobacter spp. now is considered to be a major triggering agent. Little information is available concerning the relationship between APN and Campylobacter spp. in dogs. Dr. Martinez-Anton et al investigated the association between Campylobacter spp. infection and APN. Associations with additional potential risk factors also were investigated, particularly consumption of raw chicken. Twenty-seven client-owned dogs suffering from suspected APN and 47 healthy dogs, client-owned or owned by staff members were selected. Fecal samples were collected from each enrolled animal to perform direct culture, DNA extraction, and polymerase chain reaction (PCR) for detection of Campylobacter spp. In some cases, species identification was performed by sequence analysis of the amplicon. Data were obtained from the medical records and owner questionnaires in both groups. In cases in which the fecal sample was collected within 7 days from onset of clinical signs, APN cases were 9.4 times more likely to be positive for Campylobacter spp. compared to control dogs (P < 0.001). In addition, a significant association was detected between dogs affected by APN and the consumption of raw chicken (96% of APN cases; 26% of control dogs). The most common Campylobacter spp. identified was Campylobacter upsaliensis. Raw chicken consumption is a risk factor in dogs for the development of APN, which potentially is mediated by infection with Campylobacter spp. Download article

Ischemic optic neuropathy

A case report of ischemic optic neuropathy in a dog with acute bilateral blindness and primary systemic hypertension was presented by the Centre for Small Animal Studies, Animal Health Trust. A 6-year-old neutered female Jack Russell terrier was investigated for sudden onset prechiasmatic bilateral blindness, left circling, reduced proprioception in the right pelvic limb and right facial allodynia. Electroretinography was normal. Magnetic resonance imaging (MRI) examination revealed that the right optic nerve and the optic chiasm were hyperintense on diffusion weighted imaging and hypointense on apparent diffusion coefficient map consistent with ischemic optic neuropathy. A concurrent lacunar infarct was detected in the left rostral colliculus. Primary systemic hypertension was diagnosed based on blood pressure measurement and no detectable abnormalities on hematology, comprehensive serum biochemistry, urinalysis including protein/creatinine and cortisol/creatinine ratios and thoracic/abdominal imaging. Prednisolone for 10 days and amlodipine long-term were administered. Vision was not recovered after 7 months. Repeat MRI supported the diagnosis of ischemic lesions and revealed a recent striatocapsular infarct. Ischemic optic neuropathy is a well-recognized cause of blindness in humans and should be included as a differential diagnosis for acute prechiasmatic blindness in dogs. Download article

Juvenile myoclonic epilepsy with absence seizures

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

Tiny reviews – JVIM Sept/Oct 2017

by Deena Tiches, DVM, DACVIM (Neurology)
Originally posted on the NeuroWebVet website; modified and reprinted with permission.

This issue of JVIM has three neurology articles.


Wireless EEG in the diagnosis of idiopathic epilepsy in dogs

The diagnosis of idiopathic epilepsy in dogs was improved when researchers in Canada, Germany, Finland and the US developed a wireless video EEG to be used in unsedated dogs. Eighty-one client-owned dogs were investigated for unusual behavior events. The events were described as a combination of tonic-clonic seizures, head bobbing or tremors, focal twitching/myoclonus/ spasticity (face, ears, head, neck, limbs), altered mentation, chasing/holding visible and invisible stimuli (lights, tail, “flies”), proprioceptive ataxia, and gastrointestinal upset. Diagnostic success was achieved in 72% of dogs. This technique was a reliable diagnostic tool to investigate the epileptic origin of behavioral events in dogs. Download article

Clinicopathologic and MRI features of FIP

The clinicopathologic features and MRI findings in 24 cats with histopathologically confirmed neurologic feline infectious peritonitis (FIP) was reported from research at the Royal Veterinary College, University of London. Twenty-four client-owned cats with histopathologic confirmation of neurologic FIP underwent imaging with a high-field MRI (1.5 Tesla). The clinical presentation of the 24 cases consisted of 3 distinct neurologic syndromes. Three cats presented with a T3-L3 myelopathy with no detectable brain involvement. Seven cats presented with central vestibular syndrome, including altered mental status, pronounced vestibular ataxia, and pathologic nystagmus. The remaining 14 cats presented with multifocal CNS disease with tetraparesis (14), obtundation (13), cervical hyperesthesia (6), decreased to absent menace response (6), decreased facial sensation (3), facial paresis (2), anisocoria (2), absent vestibulo-ocular reflex (2), and stupor (1). MRI abnormalities were detected in all 24 cats. Ventriculomegaly was detected in 20 (86.9%) of the 23 brains imaged. Contrast enhancement was detected after gadolinium administration in all 24 cats and was typically bilateral and symmetrical. Meningeal contrast enhancement was detected in 22 cats and was multifocal or generalized in 10, affecting the brainstem and cervical spinal cord in 5, the brainstem only in 2 and the spinal cord only in 2 cats. Ependymal contrast enhancement was present in 20 cats. Cerebrospinal fluid analysis was performed in 11 cats. Total protein concentration was increased in all 11 (mean, 9.4 g/L; median, 3.6 g/L; range, 0.85-28.8 g/L) as was total nucleated cell count (mean, 196/μL; median, 171/μL; range, 15-479/μL). Neutrophilic pleocytosis was present in 7 cats, lymphocytic pleocytosis in 2, and mixed pleocytosis in 2 cats. Cerebrospinal fluid analysis by polymerase chain reaction for feline coronavirus antigen was performed in 5 cats and was positive in all 5. Immunohistochemistry was performed on brain tissue in 10 cats; all showed positive intracellular staining for the feline coronavirus antigen. Neurologic FIP typically causes diffuse vasculitis affecting the brain and spinal cord, but rarely, cats may present with neurologic deficits suggestive of a more localized disease process. Given the difficulties distinguishing feline enteric coronavirus and the FIP virus to reach a definitive antemortem diagnosis of FIP is difficult. However, the results of this case series suggest that MRI of the brain can be a sensitive means of lesion detection in cats presented with neurologic FIP, with MRI findings reflecting leptomeningeal and ependymal vasculitis, secondary ventriculomegaly, and mass effect. Download article

Relationship of brachycephaly and hydrocephalus in Persian cats

Cat breeders began to observe a frequent occurrence of internal hydrocephalus in Persian cats with extreme brachycephalic head morphology. This led Dr. MJ Schmidt and colleagues to investigate a possible relationship among the grade of brachycephaly, ventricular dilatation, and skull dysmorphologies in Persian cats. The brachycephalic morphology of this modern “peke-face” Persian, named after the flat-faced Pekingese dog, accentuates childlike skull characteristics as it produces large round eyes and a flat face with a large forehead. This phenotype has become popular, although high grades of brachycephaly can be associated with severe health problems in Persians. The grade of brachycephaly was determined on skull models based on CT datasets for 92 Persian cats and 12 domestic short hair (DSH) cats. Compared to both DSH and doll-face Persians, a grossly reduced cranial length and increased width and height was noted in the peke-face Persians. When viewed from the front, the width of the braincase (cranial width) almost reached the lateral borders of the orbits in fourteen cats. The skull was dorsally round and dome-shaped and showed frontal bossing in all peke-face cats. The frontal sinus was small or absent in all peke-face cats. The nasal bone was found to be notably short. Eight peke-face Persians showed osseous defects in the parietal and frontal bones. Thirty-eight peke-face cats showed a prognathic mandible. The occlusal pattern of the canines and incisors was aberrant in twelve cats. Retrograde growing conchae were found in 24 cats, leading to obstruction of the ventral nasal passage. None of these findings were seen in doll-face Persians. Midsagittal MR-images revealed a displacement of the turbinates toward, or into, the cranial cavity. In peke-face Persians, the rostral aspect of the brain was compressed leading to a more circular brain shape in sagittal views. Olfactory bulbs were ventrally and laterally shifted. The corpus callosum was round, separated from the fornix, and dorsally displaced in eighteen peke-face Persians Thirty-eight cats showed cerebellar deviation into the foramen magnum, which was also seen in twelve of the doll-face Persians. In five kittens, almost half of the cerebellum herniated into the vertebral canal. Dimensions of the lateral ventricles were subjectively increased in 29 peke-face Persians. All doll-face Persians showed subjectively normal ventricular dimensions. Ventricular enlargement (ventricle-brain ratio) (P < 0.0001) and cerebellar herniation (P < 0.001) were clearly associated with the peke-face morphology. The results of this study show that the increasing emphasis on a brachycephalic phenotype can have a correlating negative impact on general skull and brain morphology in Persian cats. Download article

Not-So-Tiny Review: JVIM July/August 2017 – Myoclonus and myotonia

by Deena Tiches, DVM, DACVIM (Neurology)
Originally posted on the NeuroWebVet website; modified and reprinted with permission.

Mark Lowrie and Laurent Garosi discussed a classification system for myoclonus and myotonia, two involuntary movement (IM) disorders, in order to aid diagnosis and treatment. Myoclonic movements are sudden, brief, shock-like IMs. They are typically positive (caused by muscle contraction) and are usually are associated with movement of the affected body part, unlike twitches in which the twitch remain within the affected body segment and movement is not observed. Myoclonus can be subdivided into physiological myoclonus (e.g., hypnic jerks), essential myoclonus (idiopathic or hereditary), epileptic myoclonus, or symptomatic myoclonus. Most people are inherently familiar with myoclonus. Most of us twitch when we fall asleep and sometimes experience this “twitch” as part of a dream. These episodes are entirely normal and are called hypnic jerks, but they give a good indication of what a sudden, brief, “shock-like,” involuntary movement caused by muscular contraction would feel like. Hiccups are another example of physiological myoclonus. Epileptic myoclonus occurs in patients whose main complaint is one of epilepsy but who also exhibit myoclonus and also is seen with degenerative diseases such as Lafora’s disease or lysosomal storage diseases. Non-epileptic myoclonus is seen in dogs secondary to distemper virus encephalomyelitis. Levetiracetam and clonazepam appear to have some benefit in many types of myoclonus; levetiracetam works well with epileptic myoclonus. However, subcortical (e.g., familial reflex myoclonus in Labradors) or spinal myoclonus (e.g., CDV) are fairly non-responsive to either medication. Myotonia always occurs after a voluntary movement or after a physiological or external stimulus (e.g., percussion). After a period of rest, dogs develop marked stiffness in all 4 legs, exhibiting a “bunny-hopping” gait in the pelvic limbs for the first few steps that subsides with exercise but the gait remains abnormal. In severe cases, dogs may experience episodes of stiffening and falling sideways with all 4 limbs rigidly extended. These episodes resolve rapidly with dogs returning to ambulation but with stiffness remaining. Myotonia congenita, non-dystrophic myotonia, has been described in the Miniature Schnauzer and is inherited as an autosomal recessive trait. The disease results from a mutation in the skeletal muscle voltage-dependent chloride channel. Unfortunately, there are no safe and effective drugs available that act directly on the chloride channel. Therefore, treatment is aimed at sodium channel blockade to prevent the receptive activation of these channels and hence decrease the repetitive electrical activity of the myotonic muscle. Class 1 antiarrhythmic drugs such as procainamide (class 1A) and mexiletine (class 1B) affect sodium channel activation and have both been used successfully in the management of myotonia in people. In dogs, only higher doses of these medications resulted in clinical improvement, but the adverse events at these higher doses make them unsuitable as long-term treatment. Myotonic dystrophy has only been reported in 4 adult dogs with clinical signs similar to those of congenital myotonia. Muscle was grossly and histologically grossly abnormal, with variability in fiber size, fibrosis, rows of internal nuclei, and type I fiber atrophy. No mutation has been identified for veterinary muscular dystrophies to date.

Source: Lowrie M, Garosi L. Classification of involuntary movements in dogs: Myoclonus and myotonia. J Vet Intern Med 2017;31:979-87. Download article.