Tremors are often seen in dogs. Patients of any age or size can be treated. There are various types of tremors, including those affecting only certain muscles or body parts or those affecting the entire animal. Tremors can have a variety of causes, so diagnosing the cause can be challenging.
What are tremors?
There can be normal reasons for shivering, so it is important to take these into consideration. It is possible that the pet is:
- cold
- scared
- having a dream during sleep.
It is usually possible to exclude these as not being diseases by providing the pet with a blanket or sweater, comforting them, or waking them up.
Dogs with muscle loss (atrophy) often suffer from muscle fatigue and their muscles shake when overworked. In this type of tremoring, the patient is elderly, and the tremors usually begin after they have stood longer than they would like. A tremor helps release stored glycogen/glucose to allow muscles to continue contracting when fatigued. Once the patient relaxes and rests, the tremor generally stops.
Signs of neuromuscular disease are not usually mild shivers; they are involuntary tremors and twitches that are more severe.
What are the signs of tremors?
Tremors are characterised by regular cycles of muscle twitches, which make them rhythmical. Even if tremors are subtle or severe, their frequency should always be regular. A tremor is distinguished from twitches and other involuntary muscle contractions because of its rhythmical nature.
How do I diagnose tremors?
You need to know what type of tremor you’re dealing with in order to figure out what may be causing the pet’s tremor. There are three types of tremors: those that occur at rest, those that occur when standing, and those that occur when moving (intentionally):
1. Rest tremors are seen when the affected body part is rested and not being used.
2. Action tremors are only seen when the pet is using the affected part of the body. These tremors can be divided into two types:
(a) Postural tremor occurs when the affected body part is held against gravity (e.g. a tremor of the limbs when standing that disappears when your pet starts walking or when lying down).
(b) Kinetic tremor occurs during any type of voluntary movement. It can be present when the movement begins, during the course of movement, and as the target is reached (intention tremor).
What can cause tremors?
1) Resting tremors
· Resting tremors are very rare in dogs and cats. The best example of a resting tremor in people would be the tremor associated with Parkinson’s disease. This sort of tremor is something that we don’t come across very often in our pets.
2) Action-related kinetic tremors
· Cerebellar disease – diseases involving the cerebellum of the brain (a part that fine controls movement) will lead to tremors when the pet directs their attention to a task. The pet may sit quietly without tremors when at rest but if a bowl of food is put out, tremors of the neck and head erupt when your pet reaches for the food. This sort of tremor (called an intention tremor) generally goes way beyond what might be described as shivering or even twitching. A classic example of cerebellar intention tremors is seen in kittens born with cerebellar hypoplasia, a neurological condition stemming from the mother becoming infected with or vaccinated for feline panleucopaenia virus during pregnancy (see feline panleucopenia virus video). They are also commonly seen in storage diseases (see factsheet).
Cerebellar disease certainly does not have to be congenital (i.e. something a pet is born with). Any damage to the cerebellum (trauma, tumour, infection etc.) can produce an intention tremor. An intention tremor is highly suggestive of disease in the cerebellum, though, and diagnostics should be pursued to uncover the nature of that disease.
· Idiopathic generalised tremor syndrome – this is a condition requiring special mention and it has a number of names including idiopathic cerebellitis and ‘white shaker syndrome’. The latter term has been used as it seemed to occur commonly in young, mature (<2 years), small white-breed dogs, particularly the Maltese and West Highland white terrier. However, we now see it in a whole range of breeds of any colour. The dog may develop a sudden marked tremor of the head and limbs, that worsens with exercise, stress and excitement but disappears with sleep (see idiopathic generalised tremor syndrome video). Although classified here as an intention tremor, this condition is unusual to other types in that it can also be seen as a tremor at rest making it difficult to classify. Other signs that may be seen with the tremor are mild cerebellar signs but also a subtle balance (vestibular) disorder. Signs tend to progress over one to three days and then remain static until treatment is initiated or, in a few cases, the problem can slowly improve months later. Early in the course of the disease it is easy to misinterpret the tremor as the pet being ‘scared’ or ‘cold’. Diagnosis will involve an MRI scan of the brain and a sample of brain fluid (cerebrospinal fluid) to rule-out other conditions that can mimic this condition. This is believed to be a condition caused by the immune system attacking the brain and so medication such as corticosteroids are given to suppress this response. The prognosis is very good with the vast majority of dogs making a very good recovery.
· Shaking Puppy Syndrome – This condition has many names including hypomyelination, dysmyelination and spongiform leukoencephalomyelopathy. It is a congenital disorder affecting myelin (insulation around the nerve fibres) production in the post-natal period. Any breed of dog may be affected. The tremor becomes first apparent at an early age (range 2-8 weeks) but pups remain bright and responsive throughout. Severity of clinical signs varies between breeds yet tremors affecting the whole body that reduce or disappear at rest or sleep are a common feature (see shaking puppy syndrome video). In several breeds, affected puppies can have a gradual improvement and are normal by 12-18 months of age. The reason for this improvement is myelin production is delayed (dysmyelination) in some breeds rather than absent (hypomyelination) and affected puppies (e.g. Chow Chow and Border terrier) show a gradual clinical improvement over time. The cause is unknown although four genetic mutations have been identified to date in Springer Spaniels, Weimaraners, Border terriers and Australian cattle and Shetland sheep dogs. These can help make a definitive diagnosis. In other breeds, the only way this condition can be diagnosed is by ruling-out other diseases that look similar to this condition. An MRI scan of the brain and sample of brain fluid (cerebrospinal fluid) will need to be collected to do this. These results would be expected to be normal. There is no known treatment for this condition. Nevertheless, in some pups they can stabilise and slowly start to show improvement although they may never be normal, some pups can become adult dogs with a reasonably good quality of life.
3) Action-related postural tremors
· Orthostatic tremors – these become apparent at a young age (usually less than 2 years old) and are unique, in the sense that you’ll notice the dog being reluctant to lie down (see orthostatic tremor video). To differentiate orthostatic tremor from other types of tremors, it is important to know that orthostatic tremors completely disappear when the dog walks, runs, or lies down. Great Danes and Scottish Deerhounds are most commonly affected and these breeds also suffer from Wobblers disease and cerebellar diseases meaning orthostatic tremor can be mistaken for one of these other disorders. Affected dogs can be treated with gabapentin or phenobarbital although response to these medications is variable. The condition is not painful but can make dogs appear uncomfortable.
· Idiopathic head tremor syndrome – this is characterised by an involuntary side to side or up and down movement of the head that happens very fast (see – idiopathic head tremor syndrome video). The movement has been referred to as a head bob. The most important thing about this condition to understand it that it is completely benign, meaning it does not harm the dog at all with the uncontrolled head starting and stopping spontaneously. Dogs are completely normal in-between these episodes. Bulldogs and Dobermans are commonly affected with a hereditary basis suspected. However, any breed of dog may be affected with an average age of onset of about three years old. Episodes of tremor can last seconds, minutes or hours and tend to occur when a dog is less active or at rest meaning they are sometimes considered as ‘resting tremors’. Dogs seem able to be distracted from this movement, they remain aware, can walk and respond to commands. Tremors can be stopped when the dog is focussed on a specific activity such as eating or chasing a ball which is the opposite of what would be expected if this was an intention tremor. No treatment is required and the condition tends not to progress. If there is any concern then advanced imaging such as an MRI scan of the head can be performed for reassurance.
· Benign, idiopathic, rapid postural tremor – older dogs can develop a high frequency postural tremor of the pelvic limbs that is only seen when a dog is standing. When the pet starts to walk the tremor will completely disappear (see idiopathic Benign, Idiopathic, rapid postural tremor video). It is unknown what causes this and a steady progression with age is often seen. These tremors fulfil many of the characteristics of a resting tremor and are postural in nature although can involve features of kinetic tremor as well. The general recommendation is that this is benign and does not require treatment.