Paroxysmal dyskinesia

What causes paroxysmal dyskinesia?

It is believed that PD results from dysfunction in a brain area that controls movement. It is often unknown what causes the condition. Genetic abnormalities may cause some forms of PD in people. In some cases, paroxysmal movement disorders are caused by brain damage caused by tumours, inflammation, infections, or strokes.

It is believed that most PDs in animals are primary in nature, meaning that the pet is born with them. A specific area of the brain that plays a crucial role in controlling movement may malfunction in PD. While some genetic mutations are being identified that may provide a better understanding of these poorly understood conditions, the underlying cause often remains unknown.

In dogs, secondary dyskinesia can occur due to a number of factors, including drug administration (e.g. propofol, phenobarbital), and structural intracranial lesions. A secondary paroxysmal dyskinesia can sometimes be distinguished from a primary paroxysmal dyskinesia by additional neurological signs seen between attacks. Border terriers have been linked to a particular PD due to gluten exposure. These dogs can often have signs consistent with gut disease that can range from mild to severe in between the episodes.

What are the signs of paroxysmal dyskinesia?

It is common for dogs to develop PD at a young age, and attacks are usually triggered by startling or sudden movements. Males are particularly affected (75%) and most of these are entire.

In most cases, affected dogs have cramping or spasms in their hind limbs, but all four limbs can be affected. As a result of the spasms, animals are severely incapacitated during attacks; nevertheless, many dogs will still attempt to walk. Exercise and excitement can sometimes trigger episodes. In order to diagnose the condition, it is very beneficial for the owners to take a video of an episode during which the abnormalities are present (see video of paroxysmal dyskinesia).

Could this be epilepsy?

An epileptic seizure is the main differential diagnosis for paroxysmal dyskinesia. Both involve periods of abnormal motor activity that are self-limiting. A paroxysmal dyskinesia differs from an epileptic seizure in the following ways:

• If a pet remains alert, this does not necessarily rule out an epileptic seizure, since partial seizures can also cause this. However, if a pet has episodes where all four legs are moving or involved then for this to be an epileptic seizure we would expect the pet to not be responsive, even if their eyes remain open. Pets having a PD episode will remain aware of their surroundings.
• Lack of abnormal behaviour even after episodes lasting hours – PDs can last minutes to hours. Epileptic seizures tend to be much shorter lasting only minutes. On the rare occasion that seizure activity becomes prolonged, an obvious period of abnormal behaviour is seen where pets can appear blind, bump into things and pace around the house relentlessly. This sort of behaviour should not be seen following an episode of PD and the lack of this behaviour helps us to diagnose a PD.
• No autonomic signs – most epileptic seizures are accompanied by autonomic signs (i.e. urination, salivation or both). This is not something that is usually seen with PDs so if your pet is urinating or salivating during an episode it is more likely to be an epileptic seizure.

How do I diagnose paroxysmal dyskinesia?

The signs of PD in dogs and people are often misdiagnosed as unusual epileptic seizures. One part of the history that can help distinguish these conditions from seizures is whether a dog loses consciousness during an attack and whether signs such as loss of bladder/bowel function or excessive salivation are present. A video can really help with this process.

An MRI scan of the brain, along with collecting a sample of fluid from around the brain (cerebrospinal fluid (CSF)) for analysis is often recommended. Blood and urine tests will help rule out underlying metabolic or hormone disorders.

Is the condition the same in all pets?

Although many breeds of dog are affected by these disorders a number of breed-specific paroxysmal movement disorders have been described. These only occur in the particular breeds and each form is subtly different. If a dog is from one of the commonly affected breeds diagnosis may be more straightforward.

Cavalier King Charles Spaniels

In CKCS this condition is often called ‘episodic falling syndrome’ (EFS). Episodes are triggered by exercise, stress or excitement and affected dogs develop a gradually worsening muscle spasm in the fore and hind limbs during an attack, with the trunk also affected; this results in a characteristic ‘deer-stalking’ or ‘praying’ position (see CKCS paroxysmal dyskinesia video). Episodes begin between 14 weeks and 4 years of age and dogs are normal between episodes. The condition gets its name from the fact that all 4 limbs will often cramp during exercise and cause the dog to fall over. Other clinical signs that sometimes occur include facial muscle stiffness, stumbling, a ‘bunny-hopping’ gait, arching of the back or vocalization. A genetic test is available, so if the condition is suspected a blood sample can be taken and submitted for analysis. Most dogs respond to treatment with acetazolamide. Clonazepam can be used as add-on treatment to acetazolamide in difficult to control cases, though its beneficial effects sometimes diminish with time; other drugs can also be considered.

Scottish or Cairn terriers

In these breeds the condition may be referred to as ‘Scottie cramp’. During excitement, the hind limbs of young adult dogs typically become stiff and extended, although affected dogs occasionally have exaggerated flexion of the limbs and the forelimbs can also cramp. Severely affected dogs arch their back and may fall onto their side, with their head and tail flexed. Diagnosis is based on a dog having typical episodes and no evidence of other conditions that might appear similar. Treatment is aimed at using drugs to improve muscle relaxation or to increase serotonin levels. These dogs can also develop a skipping lameness that may only be seen at trot but that disappears at slower (e.g. walk) or faster (e.g. gallop) speeds. This lameness tends to be most obvious in the back legs and can affect one or both simultaneously.

Border terriers

Probably the best documented form occurs in Border terriers, and is often known as paroxysmal gluten sensitive dyskinesia, canine epileptoid cramping syndrome (CECS) or ‘Spike’s disease’. Episodes are very variable, ranging from a wobbly gait to an inability to stand, or cramping of belly, neck and back muscles (see Border terrier paroxysmal dyskinesia video). Currently, the most effective way to manage CECS in Border terriers is to use a gluten-free diet, although it can take several weeks for an improvement to be noted and not all dogs will respond.

Can paroxysmal dyskinesia be treated?

Paroxysmal dyskinesia can be extremely frustrating to treat. Apart from CKCSs who respond to acetazolamide and Border terriers who generally respond to exclusive gluten free diets, most cases of PD do not respond to medication. In particular, the large majority of PD do not respond to anti-epileptic medication. Treatment may be helpful if the episodes of PD occur more than once a week.

Will a pet recover from paroxysmal dyskinesia?

Episode duration and frequency varies dramatically, even within an individual, with animals often having many episodes during a few days/weeks with long periods of normality in-between. In many breeds, episodes significantly reduce in terms of frequency and duration with age. Most affected dogs are therefore not medicated and will live a perfectly normal life in-between the episodes, which are not life-threatening but more distressing for everyone involved. We usually only advise trying treatment if the frequency of the episodes of PD is reaching one, or more than one, episode a week and if the animal’s quality of life seems particularly affected. 

One-third of dogs will stop having episodes and three quarter of dogs improve with time without treatment. Dogs with cluster episodes are less likely to stop having episodes.