Myoclonus

An Owner’s Guide to Understanding Sudden Muscle Jerks in Dogs and Cats 

Introduction 

Hearing that your dog or cat has myoclonus can understandably be worrying, particularly as many owners have never heard the term before. Sudden, shock-like jerks often raise concerns about epilepsy, pain or even a spinal injury. Fortunately, although myoclonus can sometimes be associated with serious neurological disease, this is not always the case. 

The purpose of this guide is to explain what myoclonus is, why it occurs, how it is investigated and what treatment options are available. We also hope it will reassure you that many pets with myoclonus continue to enjoy an excellent quality of life, particularly once the underlying cause has been identified and appropriate treatment has been started. 

One of the most important things to remember is that myoclonus is not a diagnosis in itself—it is a clinical sign. In the same way that a cough can have many different causes, myoclonus simply describes a particular type of involuntary movement. The challenge for your veterinary surgeon or neurologist is to determine why those movements are occurring. 

What is myoclonus? 

Myoclonus (pronounced my-oh-CLONE-us) describes a sudden, very brief, involuntary muscle jerk. Many owners describe these movements as looking as though their pet has received a brief electric shock. Although the movement resembles an electric shock, it is not believed to be painful. 

The jerks usually last less than a second and can occur individually or in clusters. Some pets experience only an occasional jerk every few days, whereas others may have dozens or even hundreds of episodes throughout the day. 

Myoclonus can affect almost any part of the body. In some animals only one limb is involved, while others experience simultaneous jerks affecting the head, neck, trunk and all four limbs. 

Myoclonus may involve: 

• A single muscle  

• One limb  

• Both front legs  

• Both back legs  

• The neck  

• The whole body (generalised myoclonus)  

The movements are usually extremely rapid and cannot be voluntarily controlled. Unlike normal stretching or shivering, they occur without warning and stop just as suddenly as they begin. 

Positive and negative myoclonus 

Veterinary neurologists sometimes divide myoclonus into two forms. 

Positive myoclonus occurs when a muscle suddenly contracts. This is the type most owners notice and gives the appearance of a sudden “jump” or jerk. 

Negative myoclonus occurs when a muscle briefly stops contracting. This may cause a leg to momentarily buckle or the head to briefly drop before immediately recovering. 

Although these terms are useful medically, owners usually do not need to distinguish between them. Both simply represent different forms of the same movement disorder. 

Is myoclonus always abnormal? 

Interestingly, no. 

Both people and animals can experience completely normal forms of myoclonus. 

Examples include: 

• Hiccups.  

• The sudden body jerk that many people experience while falling asleep (known as a hypnic jerk).  

• Brief muscle twitches during dreaming.  

These are considered normal physiological events and are not a cause for concern. 

However, when sudden jerks occur repeatedly while your pet is awake, particularly if they begin later in life or become more frequent, they should always be investigated by your veterinary surgeon. 

Does myoclonus mean my pet has epilepsy? 

Not necessarily. 

This is probably the commonest misconception surrounding myoclonus. 

Many owners assume that every sudden jerk must represent a seizure. In reality, many pets with myoclonus remain completely aware during the movements. They continue looking at their owner, remain responsive and immediately carry on with whatever they were doing. 

This is very different from many epileptic seizures, during which consciousness is usually impaired. 

However, some neurological diseases can cause both myoclonus and epilepsy. In these animals, the myoclonic jerks may occur many times during the day, while more typical seizures occur only occasionally. 

One of your neurologist’s main aims is therefore to determine whether the myoclonus is: 

• occurring as part of an epilepsy syndrome,  

• occurring independently of epilepsy,  

• or being caused by an entirely different neurological condition.  

This distinction is important because it influences both the investigations recommended and the treatment chosen. 

Movement Referrals Tip 

Video footage is one of the most valuable diagnostic tools available. 

Myoclonic jerks are often very brief and may not occur during your appointment. Recording several episodes on your phone before visiting your veterinary surgeon or neurologist can be enormously helpful and, in many cases, allows the movement disorder to be recognised immediately. 

Watch a dog with generalised myoclonus 

Because myoclonus can be difficult to describe in words, watching an affected dog is often the easiest way to recognise it. 

Video 1 – Generalised Myoclonus – a dog with generalised myoclonus. Notice the sudden, brief, shock-like jerks affecting multiple parts of the body. Importantly, the dog remains conscious throughout the episode. 

How is myoclonus different from other movement disorders? 

Many neurological conditions can cause involuntary movements, and at first glance they can appear remarkably similar. Fortunately, there are several features that help distinguish them. 

Myoclonus versus tremor 

A tremor is a rhythmic back-and-forth oscillation of part of the body. Tremors usually continue for several seconds or minutes and often have a regular “shaking” appearance. 

By contrast, myoclonus consists of single, sudden jerks. Each jerk is extremely brief and often occurs without any obvious rhythm. 

A useful way of thinking about the difference is: 

• Tremor = shaking  

• Myoclonus = sudden shock-like jerks  

Myoclonus versus paroxysmal dyskinesia 

Paroxysmal dyskinesias are episodes of abnormal muscle contractions that may last several minutes. 

During these episodes dogs often remain conscious but develop twisting movements, abnormal limb positions or difficulty walking. 

Unlike myoclonus, dyskinesia episodes usually: 

• last much longer,  

• have a gradual beginning and end,  

• involve sustained abnormal postures rather than brief jerks.  

Myoclonus versus epileptic seizures 

This is often the most important distinction. 

During many myoclonic episodes: 

• your pet remains conscious,  

• responds to your voice,  

• recognises family members,  

• continues breathing normally,  

• and often resumes normal activity immediately afterwards.  

Generalised epileptic seizures are very different. During these episodes animals usually lose awareness, fall onto their side and develop rhythmic paddling movements of the limbs. Salivation, urination or defecation may also occur before a recovery period lasting several minutes. 

Some neurological diseases, however, can cause both myoclonus and epileptic seizures. This is why a careful history and good-quality video recordings are invaluable when making the diagnosis. 

Part 2 – What Causes Myoclonus? 

One of the first questions most owners ask is: 

“What is causing the jerking?” 

Unfortunately, there is no single answer. 

As we discussed in Part 1, myoclonus is a clinical sign rather than a disease. This means there are many different conditions that can cause the characteristic sudden, shock-like muscle jerks. Some are relatively benign and can be managed very successfully, while others require more extensive investigation and treatment. 

For this reason, your neurologist’s job is not simply to diagnose myoclonus, but to identify the underlying disease responsible for it. 

Although there are many possible causes, it is often helpful to think of them as belonging to three broad groups: 

• Epileptic myoclonus  

• Non-epileptic myoclonus  

• Spinal (cervical) myoclonus  

Understanding which category your pet falls into helps determine which tests are recommended and which treatments are most likely to be effective. 

Epileptic myoclonus 

In some pets, myoclonus represents a form of epileptic seizure. 

Unlike the dramatic generalised seizures that most people are familiar with, epileptic myoclonus usually consists of extremely brief muscle jerks. These may occur many times each day, while larger seizures happen only occasionally—or sometimes not at all. 

In many epilepsy syndromes, the myoclonic jerks are actually the first sign owners notice. 

Because the jerks are so brief, they are often mistaken for: 

• shivering  

• startling  

• excitement  

• muscle twitches  

• pain  

Only after a more obvious seizure develops does it become clear that the earlier movements were also part of the epilepsy syndrome. 

What conditions cause epileptic myoclonus? 

Several neurological diseases can produce myoclonus as part of an epilepsy syndrome. 

Some of the better recognised examples include: 

Lafora disease 

Lafora disease is one of the commonest inherited causes of myoclonus in dogs. 

Affected dogs often develop sudden body jerks triggered by visual stimuli, excitement or unexpected noises. Many also develop generalised epileptic seizures as the disease progresses. 

Although Lafora disease cannot currently be cured, many dogs respond well to medication that reduces both the frequency and severity of the jerks. 

Juvenile myoclonic epilepsy 

Some young dogs develop inherited epilepsy in which myoclonus is the predominant feature. 

These dogs often experience repeated brief jerks while remaining conscious, although more typical epileptic seizures may develop later. 

Fortunately, many respond well to anti-seizure medication. 

Feline audiogenic reflex seizures 

Cats can also develop epilepsy associated with myoclonus. 

One of the best recognised examples is Feline Audiogenic Reflex Seizure Syndrome (FARS). 

These cats develop sudden jerks triggered by high-frequency sounds, such as: 

• tapping a spoon on a food bowl  

• crinkling paper  

• jangling keys  

• rustling plastic bags  

Initially the episodes may consist only of brief muscle jerks, but over time some cats develop larger seizures. 

Watching an affected cat often helps owners appreciate how characteristic these sound-triggered episodes can be. 

Storage diseases 

Certain rare inherited neurological diseases, known as storage diseases, can also produce myoclonus. 

These conditions are uncommon but may be considered in young animals showing progressive neurological signs. 

Does epileptic myoclonus mean my pet loses consciousness? 

Not always. 

This surprises many owners. 

Although myoclonus can represent a form of epileptic seizure, the jerks themselves are often so brief that consciousness appears to be preserved. 

Your dog may: 

• continue looking at you  

• remain standing  

• immediately continue walking afterwards  

This is one reason why epileptic myoclonus is sometimes mistaken for a movement disorder rather than epilepsy. 

However, many epilepsy syndromes eventually produce generalised tonic-clonic seizures, during which consciousness is lost. 

Can epileptic myoclonus get worse? 

Unfortunately, some epilepsy syndromes are progressive. 

Over months or years, owners may notice: 

• more frequent jerks  

• larger muscle groups becoming involved  

• development of generalised seizures  

• changes in behaviour  

• signs of cognitive decline  

Fortunately, recognising the condition early allows treatment to begin before these signs become severe. 

Movement Referrals Tip 

If your pet develops both brief muscle jerks and more typical epileptic seizures, it is extremely helpful to record videos of both types of episode. Although they may appear related, they often provide different clues about the underlying diagnosis. 

Non-epileptic myoclonus 

Not all myoclonus is caused by epilepsy. 

In fact, many pets with myoclonus never develop seizures. 

Instead, the jerks result from abnormalities affecting different parts of the nervous system. 

These conditions are collectively referred to as non-epileptic myoclonus. 

Canine distemper virus 

Historically, canine distemper virus has been one of the best recognised causes of persistent myoclonus. 

Dogs recovering from distemper infection may be left with lifelong rhythmic muscle jerks. 

Interestingly, these jerks often continue even while the dog is asleep. 

Although the myoclonus itself usually cannot be cured, many affected dogs adapt remarkably well and continue to enjoy an excellent quality of life. 

Fortunately, widespread vaccination means this condition is now much less common than it once was. 

Startle disease 

Startle disease is an uncommon inherited neurological disorder in which affected animals show an exaggerated response to unexpected sounds or touch. 

Rather than producing epilepsy, the nervous system overreacts to sudden stimulation. 

Affected animals may: 

• suddenly become stiff  

• jerk violently  

• briefly lose balance  

• fall over  

The episodes are usually extremely stereotyped, meaning they look almost identical each time. 

Hemifacial spasm 

Hemifacial spasm affects only one side of the face. 

Instead of involving the whole body, repeated contractions occur in the muscles controlling facial expression. 

Owners often notice repeated blinking or twitching of one side of the muzzle. 

Although it can look dramatic, it is a very different condition from generalised myoclonus. 

Metabolic disease 

Occasionally, abnormalities elsewhere in the body can affect brain function sufficiently to produce myoclonus. 

Examples include: 

• severe liver disease  

• kidney disease  

• electrolyte disturbances  

• low blood sugar  

For this reason, blood tests form an important part of investigating any pet with newly developed myoclonus.

Cervical (spinal) myoclonus 

One of the most exciting developments in veterinary neurology over recent years has been the recognition that not all myoclonus originates from the brain. 

Some dogs develop sudden shock-like jerks because of disease affecting the cervical spinal cord (the neck). 

This condition is known as cervical myoclonus or spinal myoclonus. 

What does cervical myoclonus look like? 

Rather than involving the whole body, the jerks usually affect the: 

• neck  

• shoulders  

• front limbs  

Owners often describe the movements as: 

“It looks as though someone has suddenly pulled his head backwards.” 

or 

“He keeps having little electric shocks through his neck.” 

These jerks are often extremely brief but may occur repeatedly throughout the day. 

Unlike epileptic seizures, the dog remains completely aware during the episode. 

What causes cervical myoclonus? 

The commonest cause appears to be painful cervical spinal disease, particularly intervertebral disc disease. 

However, other conditions affecting the neck can occasionally produce similar signs, including: 

• inflammatory diseases  

• vascular disease  

• congenital abnormalities  

• tumours  

Because several different diseases can produce similar movements, MRI scanning is often recommended to identify the underlying cause. 

Is cervical myoclonus painful? 

The jerks themselves are not thought to be painful. 

However, the disease causing the jerks may well be. 

Many dogs with cervical myoclonus also show signs of neck pain, including: 

• reluctance to lower the head  

• crying out unexpectedly  

• stiffness  

• reduced willingness to exercise  

• difficulty turning the head  

Treating the underlying neck disease often results in a marked improvement in the myoclonus. 

Why is recognising cervical myoclonus important? 

This is an excellent example of why obtaining the correct diagnosis matters. 

At first glance, cervical myoclonus can resemble epilepsy. 

However, the treatment is completely different. 

Instead of requiring anti-seizure medication, many dogs improve once the underlying spinal disease has been successfully treated. 

This is one of the reasons why neurological examination and advanced imaging can be so valuable. 

Part 3 – Myoclonus in Older Dogs, Diagnosis and Treatment 

Myoclonus in older dogs 

Although myoclonus can occur at any age, it is being recognised increasingly often in older dogs. 

In some cases, the jerks occur as an isolated problem in an otherwise healthy senior dog. In others, they develop alongside other age-related neurological changes, such as canine cognitive dysfunction (CCD)—a condition that shares many similarities with dementia in people. 

Research in recent years has shown that myoclonus appears to be more common in older dogs than was previously appreciated. Exactly why this occurs is not yet fully understood, but it is thought that age-related changes within the brain may make some animals more susceptible to developing these sudden muscle jerks. 

It is important to remember, however, that myoclonus does not automatically mean that a dog has cognitive dysfunction. Many older dogs with myoclonus have another underlying neurological condition, which is why a thorough neurological assessment remains important. 

What is canine cognitive dysfunction? 

Canine cognitive dysfunction is a progressive condition affecting the ageing brain. It develops gradually over months or years and can result in changes to memory, learning, awareness and behaviour. 

Owners may notice signs such as: 

• Becoming disorientated in familiar surroundings.  

• Standing in corners or behind furniture.  

• Changes in sleep patterns.  

• Wandering around the house at night.  

• House-soiling despite previously being well house-trained.  

• Reduced interaction with family members.  

• Anxiety or restlessness.  

• Changes in appetite or behaviour.  

Not every dog develops all of these signs, and many show only subtle behavioural changes initially. 

Some dogs with cognitive dysfunction also develop myoclonus, although it remains unclear whether the muscle jerks are directly caused by the disease or whether both conditions simply become more common as animals age. 

Should my older dog be investigated? 

This is one of the commonest questions we are asked. 

The answer depends on several factors, including: 

• your dog’s age  

• the severity of the jerks  

• whether any other neurological abnormalities are present  

• how quickly the signs have developed  

• your dog’s overall health  

A dog that has gradually developed mild myoclonus over several years and is otherwise behaving normally may require a different approach to a younger dog that suddenly develops frequent muscle jerks alongside seizures or difficulty walking. 

For this reason, every patient should be assessed individually. 

Even if advanced investigations are not ultimately performed, a neurological examination can often provide valuable information and help determine the most appropriate next steps. 

How is myoclonus diagnosed? 

Diagnosing myoclonus involves two separate stages. 

The first is confirming that the abnormal movement is genuinely myoclonus. 

The second—and often more important—stage is identifying the disease causing it. 

Fortunately, the diagnosis often begins long before your pet arrives at the referral hospital. 

A detailed history 

One of the most important parts of the consultation is simply discussing what you have observed at home. 

Your neurologist will ask questions such as: 

• When did the jerks first begin?  

• Have they become more frequent?  

• Do they occur every day?  

• Are they triggered by excitement, exercise, noise or eating?  

• Does your pet remain aware during the episodes?  

• Have any generalised seizures occurred?  

• Are there any changes in behaviour, walking or vision?  

Although these questions may seem straightforward, the answers often provide important clues about the underlying diagnosis. 

Video recordings 

Because myoclonic jerks are usually very brief, they may not occur during your appointment. 

A clear video recorded on your phone is therefore one of the most valuable pieces of information you can provide. 

In many cases, experienced neurologists can recognise the characteristic appearance of myoclonus immediately from a good-quality recording. 

If possible, try to record: 

• the entire episode  

• what your pet was doing immediately beforehand  

• your pet’s behaviour immediately afterwards  

Avoid zooming in too closely, as seeing the whole body usually makes interpretation easier. 

Neurological examination 

A neurological examination is then performed. 

This assesses how well the brain, spinal cord and peripheral nerves are functioning. 

Many pets with myoclonus have an otherwise completely normal neurological examination. 

Others may have subtle abnormalities that provide valuable clues regarding the location of the underlying disease. 

For example, evidence of neck pain may suggest cervical spinal disease, while behavioural changes or vision abnormalities may indicate disease affecting the brain. 

Blood tests 

Blood tests are usually recommended before advanced imaging. 

Although blood tests cannot diagnose most neurological diseases directly, they are extremely useful for identifying conditions elsewhere in the body that may affect nervous system function. 

These tests may detect problems such as: 

• liver disease  

• kidney disease  

• electrolyte abnormalities  

• low blood sugar  

• inflammation or infection  

Finding one of these conditions may explain the myoclonus or influence the safest way to proceed with further investigations. 

MRI scanning 

If blood tests are normal and a neurological cause is still suspected, an MRI scan is often the next step. 

MRI provides detailed images of the brain and spinal cord and allows us to look for conditions such as: 

• inflammation  

• strokes  

• tumours  

• congenital abnormalities  

• spinal cord disease  

• intervertebral disc disease  

One of the advantages of MRI is that it can identify diseases that would not be visible on standard X-rays. 

Cerebrospinal fluid (CSF) analysis 

Following MRI, it is often appropriate to collect a small sample of cerebrospinal fluid (CSF). 

CSF is the clear fluid that surrounds the brain and spinal cord. 

Examining this fluid allows us to detect inflammation, infection and certain immune-mediated diseases that may not be visible on MRI alone. 

MRI and CSF analysis are therefore frequently complementary investigations, with each providing different pieces of information. 

Are additional tests ever required? 

Occasionally, yes. 

Depending on the individual patient, further investigations may include: 

• genetic testing for inherited diseases  

• infectious disease testing  

• muscle or nerve biopsies  

• electromyography (EMG), which measures electrical activity within muscles  

These specialised tests are required only in selected cases and are not necessary for every patient. 

Movement Referrals Tip 

It is completely understandable to wonder whether all of these investigations are necessary. The important point is that there is no single “myoclonus test”. Instead, each investigation helps to narrow the list of possible causes until the most likely diagnosis becomes clear. 

Can myoclonus be treated? 

The good news is that many forms of myoclonus can be improved, even if they cannot always be completely cured. 

The treatment chosen depends entirely on the underlying diagnosis. 

This is another reason why identifying the cause is so important. 

Treating epileptic myoclonus 

When myoclonus forms part of an epilepsy syndrome, treatment usually involves anti-seizure medication. 

One medication has proved particularly useful. 

Levetiracetam 

Levetiracetam is often our first choice for treating epileptic myoclonus. 

Many dogs and cats experience a noticeable reduction in both the frequency and severity of the jerks after treatment begins. 

It is generally well tolerated, although some animals may appear slightly sleepy during the first few days. 

If larger epileptic seizures are also present, additional anti-seizure medications may be recommended. 

Treating spinal myoclonus 

If MRI identifies disease affecting the neck or spinal cord, treatment focuses on the underlying condition rather than the jerks themselves. 

Depending on the diagnosis, treatment may involve: 

• pain relief  

• anti-inflammatory medication  

• strict exercise restriction  

• physiotherapy  

• surgery  

Many dogs improve considerably once the underlying spinal disease has been successfully treated. 

Treating inflammatory diseases 

Some inflammatory diseases affecting the brain or spinal cord respond well to medications that reduce inflammation or suppress the immune system. 

Treatment plans vary depending on the specific diagnosis and are tailored to each individual patient. 

When treatment is not necessary 

Interestingly, not every pet requires medication. 

Some animals experience only occasional myoclonic jerks that do not interfere with their quality of life. 

If investigations are reassuring and the episodes remain mild and infrequent, careful monitoring may be all that is required. 

Your neurologist will discuss the advantages and disadvantages of treatment based on your pet’s individual circumstances. 

What is the long-term outlook? 

The outlook for pets with myoclonus varies enormously because it depends entirely on the underlying disease. 

Some conditions can be treated successfully, allowing the jerks to improve dramatically or even disappear completely. 

Others are lifelong conditions that require ongoing management. 

Even in these cases, however, treatment often reduces the frequency and severity of the episodes, allowing affected pets to continue enjoying an excellent quality of life. 

Many owners are understandably concerned that every jerk indicates deterioration. 

Fortunately, this is not necessarily the case. 

Some dogs continue to experience occasional myoclonic jerks for many years while remaining happy, active companions. 

Regular re-examinations allow treatment to be adjusted if the condition changes over time. 

Part 4 – Frequently Asked Questions

 This is often the section owners read first! 

Examples include: 

Is myoclonus painful? 

Explain that the jerks themselves are not thought to be painful, although the disease causing them (for example cervical spinal disease) may be. 

Can stress or excitement make myoclonus worse? 

Explain that excitement, exercise, anxiety or sudden noises can increase the frequency of jerks in some conditions, whereas others occur completely independently of activity. 

Should I continue exercising my dog? 

Discuss how this depends on the underlying diagnosis. 

For example: 

• epilepsy – normal exercise is usually encouraged.  

• cervical spinal disease – temporary exercise restriction may be advised.  

• inflammatory disease – recommendations vary.  

Can my pet still live a normal life? 

I think this is an important question. 

Something like: 

“Fortunately, the answer is often yes. Although seeing sudden muscle jerks can be alarming, many pets continue to enjoy an excellent quality of life for many years. The key is identifying the underlying cause so that the most appropriate treatment can be started.” 

Is myoclonus inherited? 

Explain that: 

• some forms are inherited (e.g. Lafora disease)  

• many are not  

• breeding advice may be appropriate for inherited conditions.  

Will myoclonus get worse? 

Explain that it depends entirely on the underlying disease. 

Some conditions remain stable for years. 

Others are progressive. 

Does every pet need an MRI? 

Owners ask this all the time. 

Explain that MRI is often the best way of identifying the underlying cause, but not every patient requires advanced imaging. The decision depends on factors such as age, clinical signs, neurological examination findings and the owner’s goals. 

Is there anything I should monitor at home? 

Discuss: 

• frequency of jerks  

• any new seizure activity  

• changes in behaviour  

• changes in walking  

• appetite  

• medication response  

I’d even suggest a small table owners can complete. 

Date

Number of episodes

Possible trigger

Comments

This often proves invaluable during follow-up consultations. 

When should I contact my vet urgently? 

I think this section would add real value. 

Owners should seek veterinary advice promptly if: 

• myoclonus suddenly becomes much more frequent  

• generalised seizures develop  

• more than one seizure occurs in 24 hours  

• a seizure lasts longer than five minutes  

• weakness develops  

• difficulty walking develops  

• severe neck or back pain develops  

• your pet stops eating or drinking.  

This gives owners clear guidance about when the situation becomes more urgent. 

Key Points to Remember 

Finish with something like: 

Key Points 

• Myoclonus is a clinical sign, not a diagnosis.  

• It consists of sudden, brief, shock-like muscle jerks.  

• The jerks themselves are not usually painful.  

• Some forms are associated with epilepsy, while others originate from diseases affecting the spinal cord or other parts of the nervous system.  

• Recording the episodes on your phone is one of the most valuable things you can do to help your veterinary surgeon.  

• Identifying the underlying cause is essential because treatment varies between different conditions.  

Many pets respond well to treatment and continue to enjoy an excellent quality of life.  

Final thoughts 

Although seeing sudden muscle jerks can be worrying, it is important to remember that myoclonus is simply a sign that helps us identify an underlying neurological condition. Modern imaging techniques, improved understanding of movement disorders and advances in treatment mean that we are now able to diagnose and manage many causes of myoclonus far more effectively than ever before. While every patient is different, many dogs and cats with myoclonus continue to enjoy happy, active lives for years after diagnosis.