Cervical jerks as a sign of cervical pain or myelopathy in dogs

Magdalena Olender AzurVet Veterinary Specialists Center, Neurology Unit, St-Laurent-du-Var, France

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Jérôme Couturier AzurVet Veterinary Specialists Center, Neurology Unit, St-Laurent-du-Var, France

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Laure Gatel Pommery Veterinary Hospital Center, Diagnostic Imaging Unit, Reims, France

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Edouard Cauvin AzurVet Veterinary Specialists Center, Diagnostic Imaging Unit, St-Laurent-du-Var, France

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Abstract

OBJECTIVE

To describe and classify cervical muscle jerks associated with cervical pain or myelopathy and evaluate their clinical and diagnostic relevance.

ANIMALS

20 dogs with a history of unilateral or bilateral cervical jerks associated with cervical pain or myelopathy.

PROCEDURES

A retrospective study. Detailed history, complete clinical and neurological examinations, CT studies, and outcome were available for each dog. All dogs received a treatment adapted to each diagnosis. The presence or absence of jerks was evaluated at short- and long-term recheck examinations. An immediate postoperative CT scan was obtained for all cases that were treated surgically.

RESULTS

20 dogs were selected for the study, 13 of which were French Bulldogs. Jerks all presented as focal repetitive rhythmic contractions on the lateral aspect of the neck (on one or both sides). All dogs had a diagnosis of cervical intervertebral disk extrusion (IVDE), half of them at the C2-C3 level. No dogs presented with extrusion caudal to the C4-C5 intervertebral disk space. The prevalence of myoclonia among all dogs diagnosed with IVDE was 3.77% (20/530) in our hospital.

CLINICAL RELEVANCE

Cervical jerk associated with cervical pain or myelopathy may represent myoclonus and was exclusively secondary to cranial cervical IVDE in this study. Full recovery was observed following medical or surgical treatment of IVDE. The exact origin and classification of this involuntary movement has yet to be established.

Abstract

OBJECTIVE

To describe and classify cervical muscle jerks associated with cervical pain or myelopathy and evaluate their clinical and diagnostic relevance.

ANIMALS

20 dogs with a history of unilateral or bilateral cervical jerks associated with cervical pain or myelopathy.

PROCEDURES

A retrospective study. Detailed history, complete clinical and neurological examinations, CT studies, and outcome were available for each dog. All dogs received a treatment adapted to each diagnosis. The presence or absence of jerks was evaluated at short- and long-term recheck examinations. An immediate postoperative CT scan was obtained for all cases that were treated surgically.

RESULTS

20 dogs were selected for the study, 13 of which were French Bulldogs. Jerks all presented as focal repetitive rhythmic contractions on the lateral aspect of the neck (on one or both sides). All dogs had a diagnosis of cervical intervertebral disk extrusion (IVDE), half of them at the C2-C3 level. No dogs presented with extrusion caudal to the C4-C5 intervertebral disk space. The prevalence of myoclonia among all dogs diagnosed with IVDE was 3.77% (20/530) in our hospital.

CLINICAL RELEVANCE

Cervical jerk associated with cervical pain or myelopathy may represent myoclonus and was exclusively secondary to cranial cervical IVDE in this study. Full recovery was observed following medical or surgical treatment of IVDE. The exact origin and classification of this involuntary movement has yet to be established.

Introduction

Muscular jerk is a nonspecific expression describing an involuntary muscle movement. In the human and veterinary literature, the term “muscle jerk” is mostly associated with myoclonus and tremors.13

Myoclonus is a sudden, brief, shock-like involuntary movement of a muscle or a group of muscles.1,3 It is usually arrhythmic, can be positive (contraction) or negative (sudden cessation of muscle tone), and is usually, but not always, associated with a movement of a body part.1,3,4 In veterinary medicine, myoclonus can be classified as epileptic and nonepileptic.3 In human medicine, the classification is more complex and can be based on etiology and anatomy of the jerk. The etiologic classification of myoclonus varies between authors, but usually the types are physiologic, essential, epileptic, and symptomatic myoclonus (physiologic, essential, and epileptic being considered as primary myoclonus and symptomatic as secondary myoclonus). Based on anatomy, the main types are cortical, cortico-subcortical (including subcortical nonsegmental and segmental), spinal (including propriospinal and segmental), and peripheral.1,4,5

Tremor is usually described as involuntary, rhythmic, oscillatory movement of a body part. Distinguishing tremor from myoclonia may be difficult, but the keyword in its identification is “rhythmicity.” Oscillation of a body part during tremor may have variable amplitudes (eg, intention tremors), but the frequency remains unchanged.1,2

Cervical hyperesthesia is a common complaint in veterinary medicine.6,7 Several conditions have been associated with the presence of cervical pain in dogs and may be categorized into mechanical, neuropathic, and referred pain (for which the origin of the pain is not in the cervical region).69 Mechanical pain refers to pain originating from the spine or its supporting structures (such as vertebral ligaments, muscles, intervertebral disks, facet joint capsules, dorsal root ganglia, vertebral periosteum, and meninges).8,9 Neuropathic pain primarily comes from injury involving the peripheral nervous system, usually by mechanical or chemical irritation of nerve roots.9 These 2 types of pain may coexist. A common example is intervertebral disk extrusion (IVDE), in which pain involves both a mechanical component, originating from the ruptured annulus fibrosus, and a neuropathic origin, due to radicular injury by the herniated nucleus pulposus.9 Cervical radiculopathy is a specific type of neuropathic pain. The pathogenesis of radicular pain involves chemical and/or mechanical irritation of the dorsal root ganglion.10 Cervical radiculopathy may provoke symptoms in specific dermatomes in the neck, face, and upper extremity regions. The symptoms may be exacerbated by rotation of the head toward the side of the neck pain.10 The presence of cervical pain in animals is usually elicited by means of palpation or careful manipulation (flexion, extension, or rotation) of the neck.6 The signs of neck pain reported in the literature include low head carriage, reduced range of movement, resistance during flexion/extension, yelping, and caudal flinching of the ears during manipulation.6 Twitching of the cervical musculature has been reported as a sign of cervical pain, but it has not been further characterized.6 The aim of this study was to describe and characterize cervical muscular jerks associated with cervical pain and/or myelopathy and to evaluate their clinical and diagnostic relevance.

Materials and Methods

Case selection

Digital medical records of Azurvet Veterinary Specialist Center were reviewed to identify dogs that were referred between August 2013 and January 2021 to the neurology service with a history of cervical muscular jerks. Keywords used for the digital data search included “cervical myokymia,” “cervical myoclonus,” and “cervical jerks.” Dogs were included in the study if cervical jerks were observed (directly or on a video provided by the owner) by a board-certified neurologist (JC) or a second-year neurology resident (MO), a definitive diagnosis was reached, and complete medical records and diagnostic images were available for review.

Records were considered complete if the following information was available: signalment (including breed, sex, and weight at the time of consultation), history, duration of clinical signs, physical and neurologic examination findings, full records of imaging findings, type of treatment received, and long-term outcome.

Medical records review

Information evaluated for each dog included breed, age, duration of clinical signs, and treatment administered before referral. Cervical jerks were classified as unilateral, right or left, and bilateral.

Diagnostic tests and their interpretation were also reviewed. If the diagnosis was cervical IVDE, the affected intervertebral space, degree and lateralization of spinal cord compression, as well as potential foraminal involvement were recorded.

The outcome was evaluated clinically at a 2-week follow-up examination at the hospital for most of the cases treated surgically. For cases treated medically, the evaluation was performed clinically by follow-up examinations and/or by telephone interview of the owners.

All medical records were reviewed by a board-certified veterinary neurologist (JC). All diagnostic images were reviewed by a board-certified veterinary radiologist (LG). Dogs were excluded from the study if medical files or imaging records were not complete (ie, not including pre- and postcontrast studies) or if any other comorbidity was detected that might have influenced the clinical signs.

Due to the retrospective nature of the study, no ethical approval was required.

Imaging

CT studies were performed on either a 64-slice (Toshiba Aquilion 64; Canon Medical Systems Corp) or 80-slice CT scanner (Aquilion Lightning 80; Canon Medical Systems Corp). CT examinations were all performed under general anesthesia, and the dogs were placed in dorsal recumbency. For contrast- enhanced studies, iodine contrast agent was injected (iopamidol; 300 mg/mL) IV.

Pre- and postcontrast images were anonymously reviewed to evaluate the initial diagnosis. When a diagnosis of disk extrusion was made, the degree of spinal cord compression and potential asymmetry of the extruded material were noted. The degree of spinal cord compression was calculated as an area of the compressive material in the most compressive site divided by the area of vertebral canal on transverse sections multiplied by 100 (Figure 1). Degeneration of the extruded disk was assessed using its degree of mineralization and was described as nonmineralized, partially mineralized, or completely mineralized.

Figure 1
Figure 1

Postcontrast (soft tissue window) CT images of case number 11. A—Sagittal view. B—Transverse view. C—Transverse image showing area of the compressive material in the most compressive site (green border) and area of vertebral canal (blue border). The degree of spinal cord compression was calculated by dividing the area of the compressive material in the most compressive site by the area of the vertebral canal on transverse section multiplied by 100.

Citation: Journal of the American Veterinary Medical Association 261, 4; 10.2460/javma.22.11.0507

Outcome

Short-term outcome was evaluated by onsite clinical recheck 1 to 2 weeks after the initial diagnosis. Long-term outcome was assessed by telephone survey with the owners at the time of writing the study.

At short-term follow-up, owners were questioned about the persistence or absence of myoclonus. Presence of pain, neurological deficits, and myoclonus were looked for during clinical examination. Recovery was considered complete if neurological examination was normal and the dog free of pain. Myoclonus were considered absent if not observed by the owners or during clinical recheck. Therapeutic failure was defined as persistence or worsening of one of the clinical signs.

At long-term follow-up, owners were questioned about the persistence or recurrence of myoclonus, pain, or signs of cervical myelopathy. Complete recovery was defined as absence of any of these signs.

Statistical analysis

Statistical analysis was performed using a statistical software program (R Core Team 2019; R Foundation for Statistical Computing). Descriptive statistics were performed for the dog population. The prevalence of the observation of cervical jerks was calculated with an exact binomial test. A Fisher exact test was performed to evaluate the presence of myoclonus in French Bulldogs versus other breeds. Values of P < .05 were considered significant.

Results

Cases

Twenty dogs were identified following digital data search and met the inclusion criteria. The dogs were referred by general practitioners for 1 or more of the following complaints: cervical pain, low head carriage, difficulties walking, spontaneous vocalization, and cervical jerks. The breed distribution was as follows: 13 French Bulldogs, 2 Cavalier King Charles Spaniels, and 1 each of the following breeds: Chihuahua, Jack Russell Terrier, Dachshund, Beagle, and Maltese. The sex distribution was as follows: male (n = 10), female neutered (8), and female (2). The median age was 4.5 years old (mean, 5 years; range, 15 months to 10 years). Body weight varied between 3 and 15 kg (mean, 11 kg; median, 12 kg). Duration of clinical signs before examination varied between 7 days to 5 months.

Neurological examination elicited only cervical pain, without any other deficit identified, in 15 cases. One dog had proprioceptive ataxia with decreased postural reaction (paw positioning) in all 4 limbs. Four dogs had thoracic limb monoparesis.

In 19 cases, the jerks were observed during consultation (Supplementary Video S1). In 1 case, they were seen on a video recording provided by the owner (Supplementary Video S2). The cervical jerks were bilateral (8 cases), left-sided (7 cases), and right-sided (1 case). In 4 cases, the lateralization was unavailable for review. The muscle jerks seemed to affect superficial musculature (ie, the sternocleidocephalicus muscle). They disappeared during anesthesia in all dogs.

Five hundred sixty-four dogs were identified with cervical IVDE in the same period of time. The prevalence of myoclonia among all dogs diagnosed with IVDE was 3.77% (20/530) in our hospital. The prevalence of myoclonia in all French Bulldogs diagnosed with IVDE was 7.92% (13/164) in our hospital.

Procedures

All dogs had diagnosis performed by CT. Two cases had a CT myelography following standard CT. Diagnosis following CT/CT myelography was acute cervical IVDE in all cases. The results are summarized (Table 1).

Table 1

Characteristics of clinical and imaging findings.

Case No. Extrusion site (CT) Asymmetry of spinal cord compression (CT) Degree of spinal cord compression (CT) Lateralization of myoclonus Other findings (CT) Breed
1 C2-C3 Left 25% Left sided C3-C4 left-sided foraminal extrusion French Bulldog
2 C2-C3 Right 31% Bilateral French Bulldog
3 C3-C4 Left 22% Left sided Multiple chronic protrusions (C2-C3, C4-C5, C5-C6 and C6-C7) Cavalier King Charles Spaniel Chihuahua
4 C4-C5 Left 29% Not known Otitis media (right side)
5 C2-C3 Right 27% Left sided French Bulldog
6 C4-C5 Right 30% Right sided T13-L1 disk extrusion Maltese
7 C2-C3 Left 24% Not known Cavalier King Charles Spaniel
8 C3-C4 Right 36% Not known French Bulldog
9 C3-C4 Left 32% Bilateral French Bulldog
10 C2-C3 Ventral 33% Not known C5-C6 chronic extrusion French Bulldog
11 C2-C3 Left 26% Left sided C3-C4 chronic extrusion French Bulldog
12 C2-C3 Left 33% Left sided French Bulldog
13 C4-C5 Left 32% Bilateral Jack Russell Terrier
14 C3-C4 Ventral 33% Bilateral C4-C5 left-sided French Bulldog foraminal extrusion
15 C4-C5 Ventral 49% Bilateral Dachshund
16 C2-C3 Right 12% Bilateral Beagle
17 C2-C3 Ventral 38% Bilateral C6-C7 chronic extrusion French Bulldog
18 C4-C5 Ventral 40% Bilateral French Bulldog
19 C2-C3 Ventral 42% Left sided French Bulldog
20 C3-C4 Left 34% Left sided French Bulldog

— = None.

The localization of the extrusion was as follows: C2-C3 (n = 10), C3-C4 (5), and C4-C5 (5). The degree of spinal cord compression was calculated between 12% and 49%. The extrusion was ventral to the spinal cord with symmetric compression in 6 cases and asymmetric compression in the remaining cases (left-sided in 9 cases and right-sided in 5 cases). Lateralization of the extrusion was on the same side as cervical jerks in 6 cases and the opposite side in 1 case. For the rest of lateralized extrusions and all symmetric extrusions, the jerks were bilateral or the lateralization was not known. For the 3 dogs presented with forelimb lameness, the lateralization of the extrusion matched the side of the lameness in 2 of them. In 1 case the extrusion was fairly symmetric.

Four dogs also had a foraminal component, all of them with an asymmetric ventrolateral extrusion toward the same side. On 4 dogs with foraminal involvement, 2 had bilateral myoclonus and 2 had unilateral jerk ipsilateral to the foraminal extrusion.

Treatment

Dogs were treated either medically or surgically. Following a diagnosis of IVDE, surgery was advised to the owners of dogs with significant neck pain, neck pain refractory to previous medical treatment, neurological deficits, and/or moderate to marked spinal cord compression (typically > 20%). If surgery was opted for, it was performed immediately following CT or as soon as possible (within 4 days in all cases). Some dogs treated surgically had an initial medical treatment administered. Medical treatment consisted of NSAIDs (meloxicam, 0.1 mg/kg, PO; or carprofen, 4 mg/kg, PO, once daily most commonly used), gabapentin (10 mg/kg, PO, 3 times/day), tramadol (4 mg/kg, PO, 3 times/day), or a combination of these substances. The cases managed surgically were treated by standard ventral slot.

Outcome

Twelve dogs were treated medically. Nine dogs were treated with a combination of NSAID, gabapentin, and tramadol and 3 dogs with NSAID and gabapentin only. Short-term clinical follow-up examination was performed for 2 dogs treated medically (1 and 3 weeks after diagnosis). These 2 dogs were free of pain and myoclonus and neurologically normal. Three dogs failed to respond to medical treatment with a relapse of clinical signs 2 weeks, 1 month, and 1.5 months after diagnosis. The clinical signs were cervical pain in all dogs and deterioration of neurological status with ambulatory tetraparesis in 1 dog. The presence of myoclonus was not noted. These 3 dogs are further described in the surgical group.

Eleven dogs were treated surgically. Eight dogs had surgery performed directly after diagnosis and 3 dogs after therapeutic failure. Their medical treatment consisted of a combination of NSAID, gabapentin, and tramadol. For all dogs treated surgically in our hospital (11 cases), myoclonus were no longer observed the day after the surgery. At the time of discharge from the hospital, all dogs were pain free. Clinical recheck evaluation was performed for 6 of 11 dogs 2 weeks after the surgery, at which point all of them were pain and myoclonus free and neurologically normal.

Long-term follow up was made for all dogs via a telephone survey with the owners or referring veterinarian at the time of writing this study. Among surgically treated dogs, only 1 animal presented with episodes of occasional cervical pain without myoclonus after exercise. Short-term follow up for this dog was unremarkable. The remaining dogs recovered uneventfully.

Regarding medically treated dogs, 1 dog suffered from deterioration of its neurological status (without myoclonus) and was treated medically (treatment not known) and with physiotherapy. This dog eventually made a gradual but complete recovery. One dog presented with several episodes of myoclonus (described by the owners), the last one approximatively 6 years after the initial diagnosis. Among the remaining dogs treated medically (7/9), no recurrence of pain, myoclonus, or cervical myelopathy was recorded.

No further ancillary test was performed in any of the dogs in which there was suspected recurrence or deterioration of the clinical signs. The outcome is summarized (Figure 2).

Figure 2
Figure 2

Summary of short-term and long-term outcomes.

Citation: Journal of the American Veterinary Medical Association 261, 4; 10.2460/javma.22.11.0507

Discussion

In human medicine, the term myoclonus encompasses a large spectrum of signs, arising both from central and peripheral nervous systems.1,4,5 In veterinary medicine, myoclonus is usually described as a sudden, brief, shock-like involuntary movement or a sequence of repeated, often arrhythmic jerks due to sudden involuntary contraction or relaxation of 1 or more muscles. This is usually associated with movement of a body part.3

The jerks described in our study were sudden, repetitive, nonrhythmic contractions of superficial cervical musculature and disappeared during anesthesia. Persistence of jerks while the animal was sleeping was not evaluated, but it may be of interest for future studies. Comparing the different types of involuntary movements known in veterinary medicine,13 the term myoclonus appears to best describe the abrupt, shock-like muscular spasms presented in our cases. Tremor is another type of involuntary movement that may be used to describe certain jerk-like movements. However, the arrhythmic nature of the involuntary jerks in our cases did not match with the rhythmic feature defining tremors.13

Two specific types of myoclonus should be considered to describe the cervical jerks observed in our study. The first one is peripheral myoclonus, which presents as focal jerks affecting muscles in the distribution of a peripheral nerve root or nerve at the level of the nerve root involved.5 The second type of myoclonus is spinal segmental myoclonus (SSM), which usually relates to spinal cord pathology (due to spinal cord injury, herpes myelitis, or demyelinating disease in human beings). It usually consists of rhythmic movements in the area innervated by the affected spinal segment.5 A few cases of cervical segmental myoclonus associated with disk disease have been described in humans.1114 Bilateral myoclonus of the trapezius muscles after distal damage to the accessory nerve and myoclonus of muscles around the scapular region following traumatic injury to the left long thoracic nerve have also been reported.15,16 In human medicine, an anatomy/physiology-based classification of myoclonus relies on advanced neurophysiologic testing (electromyography, electroencephalograms, and somatosensory-evoked potentials), but such an approach has not yet been described in veterinary medicine.5

In humans, peripheral myoclonus present as focal jerks that are intermittent, semirhythmic, or rhythmic in the distribution of a peripheral nerve root or nerve. If we consider the cervical jerks in our dogs as being a peripheral type of myoclonus, the origin of the involuntary movement would be within 1 cervical nerve root or 1 spinal nerve of the cervical musculature.

In SSM, jerks are limited to the muscles of affected and adjacent myotomes.4 In this situation, the myoclonus generator is located in the brain stem or spinal cord.4,5 Spinal segmental myoclonus may be unilateral or bilateral, with left or right synchrony in homologous muscles. It is often resistant to supraspinal influences like voluntary movement and sleep.4 Spinal myoclonus has been associated with laminectomy, remote effect of neoplasia, spinal cord injury, postoperative pseudomeningocele, laparotomy, thoracic sympathectomy, poliomyelitis, herpes myelitis, lumbosacral radiculopathy, spinal extradural block, myelopathy due to demyelination, electrical injury, acquired immunodeficiency syndrome, and cervical spondylosis.17 We speculate that, in the case of disk extrusion, the focal spinal cord compression, ischemia, edema, or inflammatory response may induce a local myoclonus generator in the cervical spinal cord. SSM may therefore represent a second possible explanation for the myoclonus observed in our cases.

The only diagnosis associated with cervical myoclonus in our study was IVDE. Cervical acute IVDE represents between 14% and 25% of all intervertebral disk diseases in dogs.18 It is usually associated with cervical pain, but reports describing cervical jerks associated with this disease are scarce.7,18 Pain secondary to IVDE may arise from several structures, including disk, facet joint capsules, dorsal root ganglion, vertebral ligaments, vertebral periosteum, and meninges.8 The extruded material can elicit both mechanical and chemical noxious stimuli. A chemical stimulation also activates a noxious reaction. This finding could suggest that the cervical myoclonus observed in our cases were triggered by mechanical stimulation of epidural structures or chemical stimulation.

None of the dogs in our study had cervical disk extrusion caudal to the C4-C5 level. In previous studies, the site most frequently affected by cervical disk extrusion in small dogs weighing < 15 kg was C2-C3 (in both chondrodystrophic and nonchondrodystrophic breeds).19,20 In our study, all dogs weighed < 15 kg; therefore, the preferential cranial localization may only represent a statistical bias explained by the tendency of disk extrusion to be localized on more cranial sites.

The muscles implicated in jerks remain unclear. Clinical observation of the myoclonus suggests involvement of ventrolateral superficial muscles such as brachiocephalicus, omotransversarius, or sternocephalicus muscles. These muscles are innervated by external branches of the accessory nerve (brachiocephalicus, sternocephalicus, and omotransversarius muscles) and by ventral branches of cervical nerves VI and VII (part of the brachiocephalicus and sternocephalicus muscles).21 The external branch of the accessory nerve originates from the cervical spinal cord. Cell bodies of axons that form the spinal rootlets and then the external branch of the accessory nerve are located in the motor nucleus of the accessory nerve, in the lateral portion of the ventral gray column, from the first to the seventh cervical spinal cord segments. Its spinal roots emerge laterally from the spinal cord, midway between the dorsal and ventral roots of the cervical spinal nerves. The external branch of the accessory nerve courses cranially within the cervical canal, enters the cranial cavity via the foramen magnum, and joins the internal branch to exit the cranium with the vagus and glossopharyngeal nerves through the jugular foramen and tympano-occipital fissure. It then innervates the aforementioned muscles.22 Electrodiagnostic investigation would be helpful in future studies to determine which muscles are implicated.

French Bulldogs presented with cervical myoclonia more often than any other breed in this study and may be predisposed to this unusual clinical presentation. This chondrodystrophic breed is known to be strongly predisposed to IVDE.23 Morphometric studies of the cervical vertebral canal show that the ratio of the spinal cord area to vertebral canal is greater in small dogs than in large dogs.24,25 A morphometric study in French Bulldogs is lacking, and it may be interesting to evaluate a possible influence of vertebral canal conformation in this breed. The other reason for the higher number of French Bulldogs in our study may be that this breed is overrepresented in our clinic for cervical IVDE. Larger breed-wide demographic study would be necessary to compare the frequency of cervical myoclonus between French Bulldogs and other chondrodystrophic and nonchondrodystrophic breeds.

Recovery of almost all cases treated surgically (11/12) is similar to very good outcomes previously reported in ambulatory dogs treated by ventral slot.20 In medically treated dogs, it was not possible to assess the speed of recovery, as the treatment was home-administered and evaluated in the short term, mostly by the owners. Nevertheless, all except 2 dogs eventually recovered (long-term follow-up) with no further signs of myoclonia. All of the dogs that failed to respond to the initial treatment or showed relapse of clinical signs after treatment discontinuation underwent surgical intervention, after which they all recovered uneventfully as other dogs treated surgically in first intent after diagnosis. A previous report26 on dogs with suspected cervical IVDE treated medically showed a good outcome in 48.9%, while 33% of them relapsed and 18.1% had therapeutic failure. In our study, 25% of medically treated cases showed recurrence of signs that required surgery. Myoclonus disappeared immediately after surgical intervention. This suggests that mechanical stimulation of the spinal cord and/or nerve root may be implicated in the induction of myoclonia, assuming that the inflammatory reaction is unlikely to disappear immediately after surgery. However, this may also have been influenced by administration of anti-inflammatory and opioid drugs in the early postoperative period. In 1 case series,27 root-signature signs associated with lateralized disk material were treated by perineural injection of methylprednisolone or methylprednisolone with bupivacaine. This treatment may have been a solution in some of our cases with foraminal compression but was not chosen because of the significant ventral to ventrolateral spinal cord compression in all cases.

The myoclonus resolved in all of the dogs treated surgically and 8 of 9 dogs treated medically. The dog considered not completely cured presented multiple short episodes of myoclonus after exercise for a few years after the initial episode. No ancillary tests were done for further diagnosis.

There were a few limitations to consider in our study. First of all, the follow-up protocol was not uniform in our cases. Short-term follow-up was only available for 2 of 9 of medically treated dogs and 8 of 11 of those treated surgically. Long-term follow-up was only obtained by telephone interview with the owners. Minor deterioration, resolution of the signs, or further short episodes of myoclonia may therefore not be excluded as they could have been missed by the owners. Follow-up in cases that deteriorated was also not clear, as no ancillary test was performed in these animals. Consequently, the cause of the deterioration or relapse could not be documented.

A second limitation was the absence of MRI studies. CT was the only imaging modality available on-site for most of the study period. Furthermore, most of the cases were chondrodystrophic dogs, for which CT is usually carried out as a first-line imaging modality in our hospital.28 If we consider the myoclonus in our cases as a spinal segmental myoclonus, it may be important to look for intramedullary changes to further precise the diagnosis. Without MRI evaluation in our cases, it is possible that significant intramedullary lesions or minor nonmineralized foraminal involvement could have been missed. The foraminal involvement in association with cervical myoclonus would be worth considering in future studies using MRI as the main imaging modality.

In conclusion, cervical muscular jerks, suspected to represent myoclonus, are a rare clinical presentation of cervical IVDE and were not encountered with any other disease in this location in our study. Further studies are needed to determine the exact origin of these involuntary movements and detail electrodiagnostic characteristics to understand pathophysiology.

Supplementary Materials

Supplementary materials are posted online at the journal website: avmajournals.avma.org

Acknowledgments

No external funding was used in this study. The authors declare that there were no conflicts of interest.

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