Understanding Tremors in Dogs and Cats

An Owner’s Guide to Involuntary Shaking

What is a tremor?

A tremor is a rhythmic, involuntary, back-and-forth movement of part of the body. It is produced by repeated contraction and relaxation of opposing muscle groups, creating the characteristic shaking movement that owners recognise. Unlike normal movement, a tremor occurs without the animal intending to make it and cannot simply be stopped by willpower.

Tremors vary considerably in appearance. Some are so subtle that they are only noticeable when a dog is standing quietly, while others involve the entire body and can interfere with walking, eating or drinking.

A tremor may affect:

• The head.
• One limb.
• Several limbs.
• The trunk.
• The whole body.

One of the defining features of a true tremor is that it is rhythmic. In other words, the movement has a regular, repetitive pattern, rather like the movement of a pendulum or the vibration of a mobile phone. This regular rhythm helps neurologists distinguish tremors from other involuntary movements, such as muscle twitches or myoclonus, which are usually much more irregular.

Another important feature is that true tremors occur only while an animal is awake. During normal sleep, the tremor should disappear. If repetitive movements continue throughout sleep, they are unlikely to represent a true tremor and another diagnosis should be considered.

Although tremors can sometimes appear dramatic, they are not usually painful. However, the disease causing the tremor may occasionally cause discomfort or other neurological signs. For this reason, any new tremor should be assessed by your veterinary surgeon.

What does a tremor look like?

Describing a tremor in words is often difficult, which is why owners are encouraged to watch examples whenever possible.

Video 1 – Dog with a pelvic limb tremor

This video shows a dog with a rhythmic tremor affecting the back legs while standing. Notice how the shaking is regular and repetitive, rather than consisting of sudden jerks. This is a good example of the characteristic appearance of a true tremor and helps illustrate how it differs from other involuntary movements.

Tremor is a clinical sign, not a diagnosis

One of the commonest misconceptions is that “tremor” is a disease.

In reality, tremor is simply a description of a particular type of involuntary movement.

Many completely different neurological conditions can produce tremors, including:

• Inflammatory diseases affecting the brain.
• Developmental abnormalities.
• Inherited neurological disorders.
• Diseases affecting the cerebellum (the part of the brain responsible for coordinating movement).
• Certain movement disorders with no identifiable underlying cause.

This means that two dogs with very similar-looking tremors may have completely different diseases and therefore require different investigations and treatments.

Rather than asking, “What medication stops tremors?”, neurologists first ask a different question:

“What is causing this tremor?”

Answering that question is the key to deciding whether treatment is required and, if so, which treatment is most likely to help.

Why do tremors occur?

Every movement your pet makes depends on remarkable communication between the brain, spinal cord, peripheral nerves and muscles. These structures work together continuously to produce smooth, coordinated movement.

If one part of this system stops working normally, the balance between opposing muscle groups can be disrupted. Instead of producing smooth movement, the muscles begin contracting rhythmically, resulting in a tremor.

One of the most important parts of the brain involved in tremor disorders is the cerebellum.

The cerebellum acts as the body’s movement coordinator. Rather than initiating movement, it fine-tunes every action, ensuring that movements are smooth, accurate and well controlled.

When the cerebellum is affected by inflammation, developmental abnormalities or inherited disease, tremors commonly develop, particularly when the animal attempts to perform a purposeful movement such as reaching for food, drinking from a bowl or walking towards its owner.

However, not all tremors originate in the cerebellum. Tremors can also arise from other parts of the nervous system, which is one reason why identifying the underlying cause often requires a neurological examination and, in some cases, advanced imaging such as MRI.

The good news

Although tremors often look dramatic, appearance alone does not indicate how serious the underlying condition is.

Some of the most obvious tremor disorders seen in veterinary neurology have an excellent prognosis. Others respond very well to treatment, while some are so mild that medication is unnecessary.

The purpose of a neurological investigation is therefore not simply to confirm that a tremor is present, but to determine which type of tremor your pet has, what is causing it and whether treatment is likely to improve it.

Part 2 – How Neurologists Classify Tremors

One of the most important advances in veterinary neurology over recent years has been a better understanding of tremors. Rather than simply describing how a tremor looks, neurologists now classify tremors according to when they occur.

This might seem like a small detail, but it is often one of the most valuable pieces of information when trying to determine the underlying cause. In fact, by carefully observing when a tremor develops, it is often possible to narrow down the list of potential diagnoses before any tests have been performed.

For this reason, your neurologist will spend time asking questions about exactly what your pet was doing when the tremor occurred.

For example:

• Was your dog standing still?
• Did the tremor begin only when walking?
• Was it most obvious when reaching for food?
• Did it disappear when lying down?
• Has it always affected the same part of the body?

The answers to these questions often provide important clues.

Not all shaking is a tremor

Before discussing the different types of tremor, it is important to understand that not every involuntary movement is actually a tremor.

Owners understandably use the word “tremor” to describe almost any form of shaking. However, neurologists distinguish several different movement disorders because they have different causes and require different investigations and treatments.

Tremor

A tremor is rhythmic and repetitive. The movement has a regular back-and-forth appearance and usually continues for several seconds or longer.

Myoclonus

Myoclonus consists of sudden, shock-like muscle jerks.

Rather than producing continuous shaking, the movement is extremely brief, often lasting less than a second, before stopping suddenly. The jerks may occur individually or in clusters but are not rhythmic like a true tremor.

Many owners describe myoclonus as looking as though their pet has received a brief electric shock.

Muscle twitching

Muscle twitching (sometimes called muscle fasciculations) consists of small, irregular contractions affecting individual muscles.

Unlike a tremor, these movements are usually:

• irregular
• non-rhythmic
• confined to small groups of muscle fibres

Although muscle twitching may look dramatic, it represents a different neurological problem from a true tremor and is often associated with disorders affecting the peripheral nerves rather than the brain.

Shivering

Shivering is a normal physiological response that helps generate body heat.

Dogs may shiver because they are cold, anxious or excited.

Unlike neurological tremors, shivering usually resolves once the underlying cause has been removed and is not associated with neurological disease.

Seizures

Generalised epileptic seizures are usually easy to distinguish from tremors because affected animals lose awareness of their surroundings.

During a seizure, dogs and cats commonly fall onto their side, paddle their limbs, salivate and may urinate or defecate involuntarily.

By contrast, animals with tremors usually remain fully conscious and aware of what is happening around them.

The three main types of tremor

Once your neurologist has confirmed that the movement is a true tremor, the next step is to determine which type of tremor it is.

Although several classification systems exist, most tremors fall into one of three main categories.

Postural tremor

A postural tremor occurs while an animal is trying to maintain a position against gravity.

For example, the tremor may develop while:

• standing still
• sitting upright
• holding the head in a particular position

The tremor often improves or disappears when the animal lies down and no longer needs to support its body.

Several recognised neurological disorders produce postural tremors, including some forms of idiopathic tremor syndrome and orthostatic tremor.

Kinetic tremor

A kinetic tremor occurs during voluntary movement.

Rather than being present continuously, it develops only when the animal attempts to perform a purposeful action such as:

• walking
• reaching for food
• drinking
• climbing steps

The tremor often becomes more obvious as the animal approaches its intended target.

This particular form is commonly referred to as an intention tremor.

Intention tremor

Intention tremor is one of the most recognisable tremors seen by veterinary neurologists.

Owners often notice that their dog appears relatively comfortable while standing quietly, but as soon as it attempts to eat or drink, the head begins shaking more dramatically.

This occurs because the cerebellum—the part of the brain responsible for coordinating movement—is unable to accurately control the movement as the animal approaches its target.

An intention tremor does not represent a disease in itself. Instead, it tells us that there is likely to be disease affecting the cerebellum or its connections.

Recognising an intention tremor therefore helps narrow the list of possible diagnoses considerably.

Resting tremor

A resting tremor occurs when muscles are completely relaxed and not actively being used.

In human medicine, resting tremors are classically associated with Parkinson’s disease.

Fortunately, true resting tremors are exceptionally uncommon in dogs and cats.

This is reassuring because many owners worry that their pet may have “Parkinson’s disease.” Although dogs and cats can develop neurological diseases that produce tremors, naturally occurring Parkinson’s disease has not been recognised in the same way as it has in people.

Does the location of the tremor matter?

Very much so.

Neurologists pay close attention not only to when a tremor occurs but also which part of the body is affected.

For example:

• Tremors affecting the head may suggest different conditions from those affecting the whole body.
• Tremors affecting only the pelvic limbs may indicate a different group of neurological disorders from those affecting all four limbs.
• Generalised body tremors often have a different list of possible causes from isolated limb tremors.

The distribution of the tremor therefore provides another valuable clue when deciding which investigations are most appropriate.

Why does classification matter?

At first glance, two dogs may simply appear to be “shaking.”

However, once the tremors are classified, it often becomes clear that they represent completely different neurological disorders.

For example:

• A young dog with a whole-body tremor that improves during sleep has a very different list of possible diagnoses from an older dog with a head tremor that occurs only when eating.
• Likewise, a dog with an intention tremor affecting the head while reaching for food is likely to require investigation of the cerebellum rather than treatment aimed at controlling seizures.

This is why your neurologist may spend several minutes simply watching your pet stand, walk, eat or drink before recommending any investigations. Careful observation often provides as much diagnostic information as many laboratory tests.

Part 3 – Common Causes of Tremors

One of the first questions owners ask after a tremor has been recognised is:

“What causes tremors?”

The answer is that there is no single cause. Tremors are a clinical sign rather than a disease, and many different neurological conditions can produce them. Some are inflammatory and respond well to treatment, some are inherited, while others are benign conditions that require little or no intervention.

Fortunately, many of the more common tremor disorders seen by veterinary neurologists have a good or even excellent long-term outlook.

Idiopathic Generalised Tremor Syndrome

Idiopathic Generalised Tremor Syndrome (IGTS) is one of the most recognisable tremor disorders in dogs and is also one of the most rewarding to treat.

The condition typically develops suddenly over a period of one to three days. Owners often notice that their dog begins shaking all over, with the tremor gradually becoming more obvious over the following 24–72 hours.

The tremor usually affects the:

• head
• neck
• trunk
• all four limbs

Many owners initially assume their dog is frightened or cold because the tremor can resemble shivering. As the condition progresses, however, the shaking becomes persistent and more severe, prompting veterinary assessment.

The tremor often becomes worse with:

• excitement
• exercise
• stress
• attempts to move

Importantly, it usually disappears completely during sleep, which is a characteristic feature of many true tremor disorders.

Some dogs also develop mild neurological abnormalities, including subtle balance problems, abnormal eye movements or mild incoordination, although many appear completely normal apart from the tremor.

Why does it happen?

The exact cause remains unknown.

Current evidence suggests that many affected dogs develop mild inflammation within the central nervous system, particularly involving the cerebellum. Because no infectious cause has been identified in most cases, the condition is believed to be immune-mediated, although further research is still needed.

Historically, this condition became known as “White Shaker Syndrome” because it was first recognised in young white dogs such as Maltese Terriers and West Highland White Terriers.

We now know this name is misleading.

Today we recognise that any breed, any colour and almost any age of dog can develop the condition, and therefore the preferred term is Idiopathic Generalised Tremor Syndrome.

How is it diagnosed?

There is no single blood test that confirms this condition.

Instead, the diagnosis is reached by combining:

• the clinical history
• neurological examination
• MRI of the brain
• cerebrospinal fluid (CSF) analysis
• exclusion of other diseases capable of producing generalised tremors

MRI scans are often completely normal. Occasionally, CSF analysis demonstrates mild inflammation, which supports the diagnosis but is not always present.

Because other inflammatory diseases of the brain can produce similar clinical signs, advanced imaging remains an important part of the investigation in many patients.

Treatment

The encouraging news is that Idiopathic Generalised Tremor Syndrome usually responds extremely well to treatment.

Most dogs are treated with corticosteroids, such as prednisolone, to suppress the underlying inflammation. Some dogs also benefit from short-term sedative medications during the early stages while the corticosteroids begin to take effect.

Improvement often begins within several days, although complete resolution may take a number of weeks.

Once the tremors have resolved, corticosteroids are gradually reduced over several weeks or months.

One of the most reassuring aspects of this disease is that the prognosis is excellent, with the vast majority of dogs making a complete recovery.

Idiopathic Head Tremor Syndrome

Idiopathic Head Tremor Syndrome (IHTS) is another relatively common movement disorder that frequently worries owners because the episodes can appear dramatic.

Unlike Idiopathic Generalised Tremor Syndrome, this condition affects only the head.

Episodes consist of rhythmic movements of the head, which may occur:

• from side to side (“no”)
• up and down (“yes”)

The remainder of the body remains completely normal.

Dogs remain:

• fully conscious
• responsive
• aware of their surroundings

During an episode, many dogs will continue watching their owner, wagging their tail or responding to commands.

Perhaps the most remarkable feature of this syndrome is that the tremor often stops immediately if the dog’s attention is diverted.

Offering food, calling the dog’s name or encouraging movement frequently interrupts the episode altogether.

This is a unique characteristic that helps distinguish idiopathic head tremor syndrome from many other neurological disorders.

Which dogs develop it?

Bulldogs, Dobermanns, Boxers and Labradors appear over-represented, but virtually any breed may develop the condition.

Most dogs develop signs between one and five years of age, although younger and older dogs have both been reported.

Is it dangerous?

Fortunately, this condition is considered benign.

Most affected dogs remain completely normal between episodes.

The episodes themselves do not appear painful and do not damage the brain.

In many dogs they become less frequent with age and may eventually disappear altogether.

Does it need treatment?

Usually not.

Unlike epilepsy, anti-seizure medication rarely alters the frequency of episodes.

Because affected dogs remain conscious and enjoy an excellent quality of life, medication is generally unnecessary.

However, it is important to remember that not every head tremor is idiopathic.

Very occasionally, similar movements can occur secondary to structural brain disease, particularly involving the thalamus. For this reason, your neurologist may recommend MRI if there are additional neurological abnormalities, if the episodes begin later in life or if the clinical history is atypical.

Orthostatic Tremor

Orthostatic Tremor is a rare movement disorder that primarily affects giant-breed dogs.

Affected dogs develop a rapid tremor only while standing.

Owners often describe their dog as appearing:

• shaky
• weak
• reluctant to stand still

The tremor usually begins in the pelvic limbs before sometimes involving the thoracic limbs and trunk.

One of the defining characteristics is that the tremor disappears as soon as the dog starts walking, sits down or lies down.

Because the tremor is present only while standing, many owners initially believe their dog has arthritis or weakness.

Which breeds are affected?

Orthostatic tremor has been described most commonly in:

• Great Danes
• Deerhounds
• Newfoundlands

although other giant breeds may also be affected.

Most dogs develop signs during early adulthood.

How is it diagnosed?

Neurological examination is usually completely normal apart from the standing tremor.

Routine blood tests, MRI and CSF analysis are generally unremarkable.

The definitive diagnosis is made using electromyography (EMG), which demonstrates a characteristic high-frequency muscle discharge while the dog is standing.

Fortunately, the condition progresses slowly in most dogs, and many continue to enjoy a good quality of life.

Tremors affecting the cerebellum

One of the most important messages in this guide is that an intention tremor is not a disease—it is a clue.

When a tremor becomes dramatically worse as a dog attempts to perform a purposeful movement, neurologists immediately begin thinking about disorders affecting the cerebellum.

The cerebellum is responsible for coordinating movement.

When it becomes diseased, movements lose their normal precision and accuracy.

As a result, affected dogs may develop:

• intention tremors
• exaggerated limb movements (hypermetria)
• incoordination (ataxia)
• a wide-based stance
• absent menace responses despite normal vision
• abnormal eye movements (nystagmus)

Many different diseases can affect the cerebellum, including:

• inflammatory disorders
• inherited degenerative diseases
• developmental abnormalities present from birth
• certain metabolic diseases

Fortunately, most dogs with cerebellar disease do not develop tremors, so the presence of an intention tremor provides an important diagnostic clue but does not occur in every cerebellar disorder.