Department of Small Animal Medicine and Surgery, University of Veterinary Medicine—Hannover, Hannover, Germany
The most important step in the management of a ‘collapsing’ disorders is to establish the presenting complaint. A patient presented with a history of paroxysmal episodes or “fits” can provide any experienced clinician with an interesting challenge. First, the patient is usually normal at the time of presentation.
Second, the identification of the type of episode is dependent on a good description from the person who witnessed the episode. Third, most of these paroxysmal episodes appear unpredictable and uncontrollable for the owner and therefore their observation might be heavily biased by an emotionally loaded perception of reality. A detailed history is, however, vital before embarking on a diagnostic investigation. Many owners can video the events, which can help you characterise them.
Syncope, narcolepsy/cataplexy, pain, compulsive behaviour disorders, vestibular attacks, certain movement disorders, neuromuscular weakness and seizures are paroxysmal events, which share commonalities in their clinical presentation. The inter-episodic clinical examination can be normal for these presentations. Some of the animals might present with inter-episodic deficits and this will guide your clinical decision-making and help you determine the system involve (and localise the lesion within). The animals might even present with the ‘strange’ episode at your clinic, e.g., prolonged seizure activity (status epilepticus [>10 min], cluster seizures [≥2 seizure/day]) or vestibular dysfunction.
Define the Problem
Paroxysmal episodic disorders can have many presentations affecting posture, muscle tone, uncontrolled movements and alteration in behaviour. Apart from characterising the episode itself, it is important to establish any triggers or clinical signs the animal might show prior to or shortly after an episode. Common episodic events, which need to be differentiated are syncope, narcolepsy/cataplexy, behaviour changes, vestibular attacks, movement disorders, neuromuscular weakness and seizures.
Episodes of syncope are usually characterized by a sudden, short, transient loss of consciousness and postural tone. The animals are flaccid during the episode but can experience a brief myoclonic jerk just before collapsing. We have seen this especially in cats with 3rd degree atrioventricular block. This can be confused with brief focal seizures. However, most animals with syncopal episodes do not show any pre- or post-episodic signs. Syncopal episodes are commonly associated with exercise or movement rather than occurring at rest. Recovery is usually nearly instant.
There can be multiple episodes per day, which can occur shortly after each other and show no improvement on anti-epileptic drugs. In fact, antiepileptic drugs can impair cardiorespiratory function and therefore these episodes can get worse with anti-epileptic drug treatment.
Narcolepsy is a rather rare disorder of the sleep-wake cycle. Cataplectic attacks are common in narcolepsy, which can resemble syncopal collapse and seizures. Cataplectic attacks are usually triggered by food, excitement, and stress or pharmacologically (e.g., physostigmine). Following the ‘trigger’ the affected animal will become flaccid and collapse. Narcoleptic animals experience chronic fatigue, although they do not necessarily sleep more. They can be restless at night and sleepy during the day because of a disturbed and irregular sleep pattern. A history of others affected in the litter or in the breeding line is not uncommon.
Paroxysmal Behaviour Changes
Pain can be experienced episodically and trigger a behavioural response which can resemble focal seizures, e.g., nerve root impingement or irritation caused by lateral disc protrusion/extrusion resulting in ‘freezing’, myoclonic jerks, muscle spasms and/or muscle fasciculations. Behaviour disorders, such as episodes of aggression or compulsive behaviour changes (stereotypic behaviours, e.g., continuous rhythmic pacing, licking and vocalisations) can also look similar to sensory seizures. Dogs and cats are usually normal in between episodes. Compulsive behaviour changes, however, are not associated with changes in muscle tone or in the level of consciousness and usually a behavioural trigger can be identified.
Transient vestibular episodes are a rare phenomenon characterised by the same cardinal signs seen with non-intermittent vestibular disease such as head tilt, nystagmus and ataxia. Nystagmus and gait abnormalities can also be seen with seizures, but it is rare that a seizure causes a head tilt. These patients will typically have no altered consciousness during an episode and are fairly normal before and after an episode. These episodes will not respond to standard antiepileptic drug treatment.
Paroxysmal Movement Disorders
Our understanding and therefore ability to identify paroxysmal movement disorders has improved in the last decade. Most of the movement disorders are elicited or deteriorate when the animal is excited or gets stressed. They usually are associated with movements, rarely occur at rest or out of sleep, are episodic and involve an increase in muscle tone (dystonia) and do not affect the level of consciousness. Some of these paroxysmal movement disorders were formerly thought to be seizures but they lacked adequate response to standard antiepileptic drugs. In addition, they more closely resemble movement conditions described in humans and so they are now considered to be a movement disorder. Some of them have been genetically characterised.
Canine Epileptoide Cramping Syndrome
Canine epileptoide cramping syndrome (“Spikes Disease”) in border terriers is one of these examples. These episodes were formerly considered to be focal seizures, but they are now considered to be a subtype of paroxysmal dyskinesias reported in people (paroxysmal dystonic choreoathetosis). Paroxysmal dyskinesias have been classified based on phenomenology, duration of the events and precipitating factors. This last classification includes paroxysmal kinesigenic dyskinesia, if the attacks occur abruptly after a sudden voluntary movement; paroxysmal non-kinesigenic dyskinesia, if the attacks occur spontaneously; paroxysmal exertion-induced dyskinesia, if the attacks are precipitated by prolonged physical exertion, and paroxysmal hypnogenic dyskinesia, if the episodes of involuntary movements occur only during sleep. Differentiating epileptic seizures from paroxysmal dyskinesia is also challenging in people. Paroxysmal dyskinesias are distinguishable from focal seizures by the lack of secondary generalisation of motor activity as would be seen in a generalised motor seizure. However, the muscle tone is often increased on both sides of the body (e.g., extended and increased muscle tone in two or four limbs), but the consciousness is not impaired as it would be if this would be a seizure affecting both brain hemispheres. Border terriers affected by the syndrome have episodic mild tremors, dystonia and difficulties walking.
Chinook Paroxysmal Dyskinesia
A similar condition has been described in the Chinook dog. ‘Chinook paroxysmal dyskinesia’ episodes are characterised by dystonia (e.g., involuntary sustained muscle contractions causing twisted postures or repetitive movements), chorea (e.g., rapid, involuntary, non-stereotypical, semi- or non-purposeful movements of an extremity or extremities) and ballismus (e.g., violent, involuntary, non-stereotypical, rapid movement of an extremity or extremities). However, athetotic movements (slow, involuntary, non-stereotypical, non-purposeful movements of an extremity or extremities) have not been reported in these dogs. Autonomic signs are absent such as urination, defaecation and hyper-salivation. The duration of episodes can range from minutes to an hour. The episodes are not triggered by sudden movement and the animals are normal before and after an episode. However, after the episodes dogs can appear tired—most likely because of the prolonged sustained increased muscle activity.
Episodic falling in cavalier King Charles spaniel is an example of a paroxysmal exertion-induced dyskinesia, which is typically aggravated or induced by stress, excitement or exercise. It is characterised by episodes of increased muscle tone (muscular hypertonicity) of the limbs. These dogs appear not to be able to relax the affected muscles and can have a “deer-stalking” gait. The back can become arched and the head lowers to the ground before the dog falls over. These dogs appear normal following an episode and have a normal mentation during an episode. The episodes last from seconds to minutes. Concurrent autonomic signs have not been reported in this disorder.
Idiopathic Head Tremor
Movement disorders can affect specific body parts such as the head in idiopathic head tremors (“head bobbing”), which are described in dogs such as the Doberman pinscher, bulldog or boxer. The head tremor has usually a frequency of 5/s, can be vertical and/or horizontal in direction, lasts seconds to hours, can occur multiple times per day, be triggered by certain positioning of the head and can be aggravated by stress or excitement. The tremors can be stopped or reduced when the animal is distracted (e.g., food). No autonomic signs have been described and the animal has appropriate mentation during an episode.
As a rule of thumb, if you are presented with a purebred dog which has an paroxysmal episode that does not cause autonomic dysfunction, is normal post episode, does not look like a generalised tonic-clonic seizure, has appropriate mentation during an episode even if changes in muscle activity are bilateral and/or does not respond as well to antiepileptic drugs, you should consult the relevant internet databases for a breed specific movement disorder.
In brief, these paroxysmal movement disorders usually lack:
- An identifiable precipitating event like an aura (sensory seizure activity, such as behaviour change [attention seeking, sniffing, starring], lasting a couple of minutes just prior to the motor seizure activity).
- Autonomic signs (e.g., hypersalivation, urination, defaecation) generalisation of increased motor activity (e.g., generalised tonic or tonic-clonic seizure).
- An impairment of consciousness. Usually dogs with impaired consciousness will not be able to look in the owner’s eyes during the event and this is a good question to ask the owner. Animals will also often not listen to the owner due to the impairment of consciousness, although this is often falsely under reported due to the owner’s perception of the event.
The brain is a ‘complex’ structure but has only ‘simple’ (limited) ways of expressing dysfunction. A seizure is a clinical sign caused by forebrain dysfunction—it is not a diagnosis (one specific disease). A plethora of structural and functional causes can result in seizures (see below when we talk about defining the lesion). Seizures can have many forms depending on which part of the brain is affected by seizure generation and propagation, e.g., a seizure could just affect a specific part of the sensory cortex and the animal might only have a change in behaviour (starring, freezing, sniffing, etc.) or only one part of the motor cortex is affected and the animal only demonstrates orofacial automatisms. The location of the ‘symptomatogenic’ zone (area of the brain causing the observed clinical signs) usually overlays or is close to the epileptogenic zone (area of the brain causing the seizure) and therefore indicates the origin of the seizure.
Seizure semiology, using clinical signs of cerebral dysfunctions caused by a seizure, not only helps to confirm that the event is a seizure, but also provides information about its origin. It is relatively simple and is clinically and cost effective. Depending on the brain areas or parts being affected by the seizure motor, sensory (including behaviour changes) and vegetative changes and automatisms can be differentiated and help to characterise the seizure event.
Is It a Seizure?
- Increased muscle tone is far more likely in seizures. The most common recognised seizure is a generalised tonic-clonic seizure. Most commonly, the animal first goes stiff (tonic phase), loses proprioception and collapses into lateral recumbency, then the tonic-clonic phase (rhythmic alternating muscle contractions) starts followed often by running movements (automatisms). Atonic seizures are very uncommon, and a ‘floppy’ collapse should guide the clinician to ‘think’ syncope or cataplexy.
- Rhythmic alternating muscle contractions are common in both focal and generalised seizures.
- Seizures often first involve the head and facial muscles (eye or facial muscle twitching).
- Stereotypical—most animals will have only one (or two) type(s) of seizure (seizure onset generalized, focal seizure onset with or without secondary generalisation). Seizures in an animal typically originate from the same epileptic focus and spread following the same brain pathways.
- The ictus (seizure itself) normally lasts 1–2 minutes.
Most seizures exhibit several stages:
- Pre-ictal behaviour changes (prodrome [hours to days] and/or aura [minutes]).
- Post-ictal behaviour or neurological deficits (hours to days).
Apart from the seizure itself, it is the post-ictal changes that are recognised by the owner.
- Common post-ictal dysfunctions are:
- Behaviour changes such as fear, aggression and disorientation.
- Increased appetite.
- Compulsive pacing.
- Blindness, usually with normal pupillary light reflexes consistent with “central” blindness.
- Menace response deficits.
- Miosis contralateral to the lesion (if one lesion [secondary to disinhibition of the oculomotor nucleus]).
- Gait abnormalities especially ataxia and “conscious.”
- Proprioceptive (paw position) deficits.
- Seizures often, but not always, occur at rest or while sleeping.
- Seizures usually impair the consciousness of the animal.
- Most of the seizure disorders will at least initially respond to antiepileptic treatment.