Understanding muscle twitching and stiffness in dogs
What are myokymia and neuromyotonia?
Myokymia and neuromyotonia are uncommon movement disorders that affect the nerves supplying the muscles. They cause muscles to become overactive, leading to twitching, stiffness and, in some dogs, episodes of collapse.
Although they are closely related, they are not the same condition.
Myokymia describes the muscle twitching that can be seen beneath the skin.
Neuromyotonia describes the more severe syndrome in which muscles become continuously active and are unable to relax properly, resulting in marked stiffness and difficulty moving.
Some dogs have myokymia alone, whereas others develop both myokymia and neuromyotonia.
What is myokymia?
Myokymia is caused by continuous overactivity of the nerves supplying the muscles, producing fine rippling movements beneath the skin.
Owners commonly describe it as looking like:
• worms moving underneath the skin
• ripples travelling through the muscles
• waves passing across part of the body.
Unlike tremor, myokymia usually does not move the whole limb. Instead, the movement remains within the muscle itself and can often be seen most clearly when the dog is resting.
► Watch Video 1 to see an example of myokymia.
What is neuromyotonia?
Neuromyotonia is a more advanced form of peripheral nerve hyperexcitability in which muscles remain continuously active and fail to relax normally.
Affected dogs may:
• become very stiff
• struggle to stand or walk normally
• collapse into a rigid, outstretched posture
• become extremely hot during prolonged episodes because the muscles are working continuously.
► Watch Video 2 to see an example of neuromyotonia.
What causes these conditions?
Both conditions occur because the nerves supplying the muscles become overactive.
In some dogs this develops because of an underlying neurological disease affecting the brain or peripheral nerves. In others it appears to be inherited. Jack Russell Terriers and Parson Russell Terriers are particularly recognised, often in association with abnormalities affecting the cerebellum. Similar disorders have also been reported in Border Collies and Yorkshire Terriers.
Sometimes no underlying cause can be identified.
Is it painful?
Mild myokymia is not usually painful and many dogs appear comfortable despite the muscle twitching.
Neuromyotonia can have a much greater impact on quality of life because the continuous muscle activity causes marked stiffness and makes movement difficult. During prolonged episodes, affected dogs can overheat because their muscles are working continuously.
Could this be epilepsy?
These conditions are movement disorders rather than epileptic seizures.
Unlike most seizures:
• dogs usually remain aware of their surroundings
• they often respond to their owners
• salivation, urination and loss of consciousness are usually absent
• recovery is generally immediate once the episode finishes.
Video recordings are extremely helpful and often provide the most useful information when making a diagnosis.
How are they diagnosed?
Diagnosis begins with a detailed history and careful review of video recordings. Blood tests are usually performed to exclude other illnesses.
Referral to a veterinary neurologist may be recommended. Additional investigations may include MRI scanning and electromyography (EMG), which records the electrical activity of muscles and can identify the characteristic electrical patterns associated with myokymia and neuromyotonia.
Can they be treated?
Treatment depends on the underlying cause.
Where possible, any underlying disease should be treated. When no cause is identified, medications that reduce abnormal muscle activity may improve comfort and mobility. Mexiletine is commonly used, while procainamide may be appropriate in some dogs.
Dogs experiencing severe episodes of neuromyotonia can become dangerously hot because of continuous muscle activity. Cooling with cold water while seeking urgent veterinary attention is therefore recommended during severe attacks.
What is the long-term outlook?
The outlook depends on the underlying cause.
Mild myokymia may remain stable for long periods and require little or no treatment. Dogs with neuromyotonia generally develop progressive stiffness over time and often require lifelong medication.
Although treatment can substantially improve quality of life, some dogs eventually develop episodes that become increasingly difficult to control. During severe attacks, overheating is the greatest immediate concern, so prompt veterinary attention should always be sought.
Key points
• Myokymia and neuromyotonia are movement disorders, not epileptic seizures.
• Myokymia causes fine rippling movements within muscles.
• Neuromyotonia causes continuous muscle activity leading to stiffness and collapse.
• Most dogs remain aware during episodes.
• Video recordings are extremely valuable for diagnosis.
• Treatment can improve quality of life, although long-term management is often required.