Classification of involuntary movements in dogs: Tremors and twitches

The Spontaneous Incidence of Neurological Clinical Signs in Preclinical Species Using Cage-side Observations or High-definition Video Monitoring: A Retrospective Analysis

When conducting toxicology studies, the interpretation of drug-related neurological clinical signs such as convulsions, myoclonus/myoclonic jerks, tremors, ataxia, and salivation requires an understanding of the spontaneous incidence of those observations in commonly used laboratory animal species. The spontaneous incidence of central nervous system clinical signs in control animals from a single facility using cage-side observations or high definition video monitoring was retrospectively analyzed. Spontaneous convulsions were observed at low incidence in Beagle dogs and Sprague-Dawley rats but were not identified in cynomolgus monkeys and Göttingen minipigs. Spontaneous myoclonic jerks and muscle twitches were observed at low incidence in Beagle dogs, cynomolgus monkeys, and Sprague-Dawley rats but were not seen in Göttingen minipigs. Spontaneous ataxia/incoordination was identified in all species and generally with a higher incidence when using video monitoring. Salivation and tremors were the two most frequent spontaneous clinical signs and both were observed in all species. Data from the current study unveil potential limitations when using control data obtained from a single study for toxicology interpretation related to low incidence neurological clinical signs while providing historical control data from Beagle dogs, cynomolgus monkeys, Sprague-Dawley rats, and Göttingen minipigs.

Idiopathic and structural episodic nonintentional head tremor in dogs: 100 cases (2004-2022)

BACKGROUND

Although idiopathic episodic head tremor (IEHT) in dogs is well-known, little is known about structural brain lesions causing structural episodic head tremor (SEHT).

HYPOTHESIS/OBJECTIVES

Describe semiology, magnetic resonance imaging (MRI) findings and outcome of dogs with IEHT or SEHT. We hypothesized that structural lesions affecting the middle cranial fossa or mesencephalic aqueduct could lead to SEHT.

ANIMALS

One hundred dogs with IEHT (n = 71) or SEHT (n = 29).

METHODS

Retrospective, multicenter, study of dogs with episodic (nonintentional) head tremor and brain MRI between 2004 and 2022.

RESULTS

Lesions on MRI in SEHT dogs were localized to the middle cranial fossa (15/29), cerebrocortex (3/29), brainstem (2/29), fourth ventricle (1/29) or multifocal (8/29) with thalamus involvement (6/8). Secondary compression of the mesencephalic aqueduct (19/29), third ventricle or interthalamic adhesion or both (14/29) was common. The most common underlying condition in dogs with SEHT was a pituitary mass. Dogs with SEHT were older, had additional neurological signs and were more likely to be euthanized after diagnosis (P < .001 for all) compared to IEHT dogs. Two SEHT dogs had only tremor. In IEHT dogs, 8/10 owners reported that the tremor decreased or abated over time (range, 106-2315 days) without treatment. Tremor remission occurred in SEHT dogs treated for underlying meningoencephalitis.

CONCLUSIONS AND CLINICAL IMPORTANCE

Presence of additional neurological signs and older age may indicate an underlying structural cause for episodic (nonintentional) head tremor involving the mesencephalic aqueduct, third ventricle, interthalamic adhesion or some combination of these. An intracranial structural abnormality cannot be excluded in dogs with normal neurological examination.

Very-Low-Frequency Spike-Wave Complex Partial Motor Seizure Mimicking Canine Idiopathic Head Tremor Syndrome in a Dog

Canine idiopathic head tremor syndrome (CIHTS) represents a benign condition characterized by episodic, uncontrolled movement of the head. Even though the condition might be an expression of a partial motor epilepsy, to date, there is a limited number of studies describing the electroencephalographic features. In this report, we describe the case of a dog diagnosed with partial motor epilepsy resembling CIHTS symptomatology, a new slow spike-wave complex pattern similar to that of Lennox-Gastaut syndrome in humans identified on electroencephalographic examination. We also studied the efficacy of phenobarbitone therapy over a period of two years.

Suspected Generalized Neonatal Tetanus in a Litter of Puppies

Tetanus, caused by Clostridium tetani neurotoxin, is extensively described in adult dogs and is frequently associated with a recent history of wounds. Although this condition is reported in 2-3 mo old puppies, tetanus has not been described in neonates. Herein, we report the clinical signs of 3-5 day old American Bully puppies from the same litter, presenting with an acute onset of marked generalized stiffness of the extensor muscles, trismus, and an inability to suckle. Three puppies died because of tetanus: one died during consultation, one was euthanized owing to respiratory distress, and the third died 1 mo after initial presentation following deterioration. All three of these puppies were clinically affected by omphalitis. Complete bloodwork, toxicological screening (including strychnine assay), serology, and polymerase chain reaction tests for selected infectious diseases were unremarkable. Necropsy of the euthanized puppy confirmed suppurative omphalitis, which may have contributed to C. tetani infection. These are the first cases of suspected neonatal tetanus in puppies, which is a frequent condition in newborn humans and is associated with omphalitis as the route of infection.

Idiopathic generalised tremor syndrome in dogs

BACKGROUND

Idiopathic generalised tremor syndrome (IGTS) causes tremor and often vestibulocerebellar signs. Previous publications on IGTS in dogs are restricted to case reports or lack exclusion of structural causes.

METHODS

Medical records of 75 dogs diagnosed with IGTS that had undergone magnetic resonance imaging (MRI) of the brain were collected retrospectively.

RESULTS

Crossbreeds were affected most commonly (41.3%), followed by West Highland white terriers (14.7%) and cocker spaniels (10.7%). A higher proportion of females were affected than males (68.0%). Median age of the affected dogs was 17 months (range 6-121 months), and median bodyweight was 9.15 kg (range 2.9-26 kg). All dogs presented with tremors and most experienced concomitant neurological signs (93.3%). Seventeen (22.7%) were hyperthermic and 31 (41.3%) had gastrointestinal signs. MRI of the brain was normal in most of the cases, and cerebrospinal fluid analysis frequently revealed mild pleocytosis. All animals were treated with prednisolone, and 39 (51.3%) also received diazepam. Median follow-up time was 13 months (range 0-134 months). The overall outcome was good, although 16 (21.3%) patients were reported to have relapsing clinical signs and 10 (13.2%) patients experienced persistent mild clinical signs.

CONCLUSIONS

IGTS should be suspected in any dog with generalised tremor and vestibulocerebellar signs with younger and smaller dogs more commonly affected.

Primary orthostatic tremor and orthostatic tremor-plus in dogs: 60 cases (2003-2020)

BACKGROUND

Orthostatic tremor (OT) is a rare movement disorder characterized by high-frequency (>12 Hz) involuntary, rhythmic, sinusoidal movements affecting predominantly the limbs while standing.

OBJECTIVE

To describe the signalment, presenting complaints, phenotype, diagnostic findings, treatment, and outcome of a large sample of dogs with OT.

ANIMALS

Sixty dogs diagnosed with OT based on conscious electromyography.

METHODS

Multicenter retrospective case series study. Dogs were included if they had a conscious electromyography consistent with muscle discharge frequency >12 Hz while standing.

RESULTS

Fifty-three cases were diagnosed with primary OT (POT). Giant breed dogs represented most cases (83%; 44/53). Most dogs (79%; 42/53) were younger than 2 years of age at onset of signs, except for Retrievers which were all older than 3.5 years of age. The most common presenting complaints were pelvic limb tremors while standing (85%; 45/53) and difficulty when rising or sitting down (45%; 24/53). Improvement of clinical signs occurred in most dogs (85%; 45/53) treated medically with phenobarbital, primidone, gabapentin, pregabalin or clonazepam, but it was mostly partial rather than complete. Orthostatic tremor-plus was seen in 7 dogs that had concurrent neurological diseases.

CONCLUSIONS AND CLINICAL IMPORTANCE

Primary OT is a progressive disease of young, purebred, giant/large-breed dogs, which appears to begin later in life in Retrievers. Primary OT apparently responds partially to medications. Orthostatic tremor-plus exists in dogs and can be concomitant or associated with other neurological diseases.

International veterinary canine dyskinesia task force ECVN consensus statement: Terminology and classification

Movement disorders are a heterogeneous group of clinical syndromes in humans and animals characterized by involuntary movements without changes in consciousness. Canine movement disorders broadly include tremors, peripheral nerve hyperexcitability disorders, paroxysmal dyskinesia, and dystonia. Of these, canine paroxysmal dyskinesias remain one of the more difficult to identify and characterize in dogs. Canine paroxysmal dyskinesias include an array of movement disorders in which there is a recurrent episode of abnormal, involuntary, movement. In this consensus statement, we recommend standard terminology for describing the various movement disorders with an emphasis on paroxysmal dyskinesia, as well as a preliminary classification and clinical approach to reporting cases. In the clinical approach to movement disorders, we recommend categorizing movements into hyperkinetic vs hypokinetic, paroxysmal vs persistent, exercise‐induced vs not related to exercise, using a detailed description of movements using the recommended terminology presented here, differentiating movement disorders vs other differential diagnoses, and then finally, determining whether the paroxysmal dyskinesia is due to either inherited or acquired etiologies. This consensus statement represents a starting point for consistent reporting of clinical descriptions and terminology associated with canine movement disorders, with additional focus on paroxysmal dyskinesia. With consistent reporting and identification of additional genetic mutations responsible for these disorders, our understanding of the phenotype, genotype, and pathophysiology will continue to develop and inform further modification of these recommendations.

Clinical findings, neurological manifestations and survival of dogs with insulinoma: 116 cases (2009-2020)

OBJECTIVES

To review the clinical findings and outcome in dogs diagnosed with insulinoma, and to assess which factors are predictors of overall survival. Additionally, to describe the neurological manifestations of this population and their correlation with survival.

MATERIALS AND METHODS

Retrospective multicentric study of canine insulinoma cases (2009 to 2020). Signalment, clinical history, neurological examination, diagnostic findings, treatment and outcome were obtained from clinical records. Univariate and multivariate analyses were used to compare the overall survival.

RESULTS

One hundred and sixteen cases were included. Median duration of clinical signs before presentation was 1.5 months. The most common presenting clinical signs were weakness (59.5%), epileptic seizures (33.6%) and changes in consciousness or behaviour (27.6%). Three dogs were suspected to have paroxysmal dyskinesia. Thirty-two dogs had an abnormal neurological examination, most commonly showing obtundation (28.1%), decreased withdrawal reflexes (21.9%) and absent menace response (18.8%). Overall survival for dogs undergoing surgery (20 months) was significantly longer than in medically treated (8 months; adjusted hazard ratio: 0.33; 95% confidence interval: 0.18, 0.59). Presence of metastases was the only other variable associated with prognosis (adjusted hazard ratio 1.72; 95% confidence interval: 1.02, 2.91).

CLINICAL SIGNIFICANCE

Clinical signs of canine insulinoma are vague and non-specific. Weakness, epileptic seizures and changes in mentation or behaviour were the most commonly reported. Obtunded mentation and forebrain neurolocalisation were the main neurological manifestations. Dogs undergoing surgery had a longer overall survival compared to medically treated cases, and dogs with metastasis had a shorter overall survival regardless of treatment modality. Abnormalities in the neurological examination did not correlate with prognosis.

Imepitoin for treatment of idiopathic head tremor syndrome in dogs: A randomized, blinded, placebo-controlled study

Background

Idiopathic head tremor syndrome is a paroxysmal movement disorder of unknown etiology. Spontaneous remission may occur, but owners may request treatment in severely affected dogs with continued episodes. Controlled studies of the disease are not available.

Hypothesis/Objectives

A drug with gamma amino butyric acid‐ergic and anxiolytic effects will decrease head tremor episodes.

Animals

Twenty‐four dogs with severe nonremitting head tremor and presumptive clinical diagnosis of idiopathic head tremor syndrome.

Methods

Prospective, blinded, placebo‐controlled clinical trial to compare imepitoin with placebo in dogs with frequent episodes of idiopathic head tremor. Evaluation of efficacy used the quotient T2/T1 that represented prolongation of the head tremor‐free period compared to a 3‐month baseline. A dog was considered a responder if tremors subsided or if the head tremor‐free period was 3× longer than the longest period during baseline (T2/T1 ≥ 3). Sample size calculations considered a large effect of imepitoin on T2/T1 (Cohen's d = 0.8).

Results

There were no responders in the placebo group (0/12). In the imepitoin group, the responder rate was 17% (2/12; P = .18) with T2/T1 3.8 and 4.0. Mean T2/T1 was 1.0 ± 1.4 in the imepitoin and 0.4 ± 0.4 in the placebo group (P = .37).

Conclusion and Clinical Importance

Imepitoin did not result in a significant overall benefit. Future studies should focus on treatment of subgroups with a common pathophysiology and similar comorbidities.

Spongiform leucoencephalomyelopathy in border terriers: clinical, electrophysiological and imaging features

A novel spongiform leucoencephalomyelopathy was reported in border terrier puppies in 2012 causing a shaking puppy phenotype, but no information regarding clinical progression, imaging or electrophysiological findings were available. The aim of the present study was to describe the clinical, electrophysiological and MRI features of this disease in seven dogs and compare them with human white matter disorders. All cases presented with cerebellar ataxia and severe generalised coarse body tremors, which started at three weeks of age. The three cases that were not euthanased showed slow but progressive improvement over several months. Brainstem auditory evoked response demonstrated a normal wave I, reduced amplitude of wave II and an absence of waves III-VII. MRI revealed bilateral and symmetrical T2-weighted hyperintensities affecting the brainstem and cerebellar white matter. Histological examination of the brain and spinal cord showed spongiform change affecting the white matter of the cerebellum, brainstem and spinal cord with decreased myelin content. In summary, this leucoencephalomyelopathy has a pathognomonic clinical presentation with defining MRI and electrophysiological characteristics, and it is the first report to describe a long-term improvement of this condition.

Classification of Involuntary Movements in Dogs: Myoclonus and Myotonia

Myoclonus is a sudden brief, involuntary muscle jerk. Of all the movement disorders, myoclonus is the most difficult to encapsulate into any simple framework. On the one hand, a classification system is required that is clinically useful to aid in guiding diagnosis and treatment. On the other hand, there is need for a system that organizes current knowledge regarding biological mechanisms to guide scientific research. These 2 needs are distinct, making it challenging to develop a robust classification system suitable for all purposes. We attempt to classify myoclonus as “epileptic” and “nonepileptic” based on its association with epileptic seizures. Myotonia in people may be divided into 2 clinically and molecularly defined forms: (1) nondystrophic myotonias and (2) myotonic dystrophies. The former are a group of skeletal muscle channelopathies characterized by delayed skeletal muscle relaxation. Many distinct clinical phenotypes are recognized in people, the majority relating to mutations in skeletal muscle voltage‐gated chloride (CLCN1) and sodium channel (SCN4A) genes. In dogs, myotonia is associated with mutations in CLCN1. The myotonic dystrophies are considered a multisystem clinical syndrome in people encompassing 2 clinically and molecularly defined forms designated myotonic dystrophy types 1 and 2. No mutation has been linked to veterinary muscular dystrophies. We detail veterinary examples of myotonia and attempt classification according to guidelines used in humans. This more precise categorization of myoclonus and myotonia aims to promote the search for molecular markers contributing to the phenotypic spectrum of disease. Our work aimed to assist recognition for these 2 enigmatic conditions.

Codon 141 polymorphisms of the ovine prion protein gene affect the phenotype of classical scrapie transmitted from goats to sheep

Background

A study to investigate transmission of classical scrapie via goat milk was carried out in sheep: firstly, lambs were challenged orally with goat scrapie brain homogenate to confirm transmission of scrapie from goats to sheep. In the second study phase, milk from scrapie-infected goats was fed to lambs. Lambs were selected according to their prion protein gene (PRNP) genotype, which was either VRQ/VRQ or ARQ/ARQ, with or without additional polymorphisms at codon 141 (FF₁₄₁, LF₁₄₁ or LL₁₄₁) of the ovine PRNP. This report describes the clinical, pathological and molecular phenotype of goat scrapie in those sheep that progressed to clinical end-stage.

Results

Ten sheep (six VRQ/VRQ and four ARQ/ARQ, of which three FF₁₄₁ and one LL₁₄₁) challenged with one of two scrapie brain homogenates, and six pairs of sheep (ARQ, of which five LL₁₄₁ and seven LF₁₄₁) fed milk from six different goats, developed clinical disease, which was characterised by a pruritic (all VRQ/VRQ and LL₁₄₁ sheep) or a non-pruritic form (all LF₁₄₁ and FF₁₄₁ sheep). Immunohistochemical (IHC) examination revealed that the pattern of intra- and extracellular accumulation of disease-associated prion protein in the brain was also dependent on PRNP polymorphisms at codon 141, which was similar in VRQ and LL₁₄₁ sheep but different from LF₁₄₁ and FF₁₄₁ sheep. The influence of codon 141 was also seen in discriminatory Western blot (WB), with LF₁₄₁ and FF₁₄₁ sheep showing a bovine spongiform encephalopathy-like profile (diminished reactivity with P4 antibody) on brain tissue. However, discriminatory WB in lymphoid tissues, and IHC pattern and profile both in lymphoid and brain tissue was consistent with classical scrapie in all sheep.

Conclusions

This study provided further evidence that the clinical presentation and the pathological and molecular phenotypes of scrapie in sheep are influenced by PRNP polymorphisms, particularly at codon 141. Differences in the truncation of disease-associated prion protein between LL₁₄₁ sheep and those carrying the F₁₄₁ allele may be responsible for these observations.

Electronic supplementary material

The online version of this article (doi:10.1186/s12917-017-1036-1) contains supplementary material, which is available to authorized users.