A dog is shaking in the consult room. Is it frightened? Painful? Toxic? Pyrexic? Neurological? Or is what you’re looking at not actually a tremor at all?
Involuntary movements are common in dogs and cats, but describing everything as a “tremor” can quickly send the diagnostic investigation in the wrong direction.
At Movement, one of the first questions we ask is very simple:
Is it a tremor or a twitch?
That distinction can tell us a surprising amount about where the problem might be coming from.
What is a tremor?
A true tremor is a rhythmic, involuntary, oscillatory movement.
The key word is rhythmic. Watch the movement carefully and there should be a reasonably regular frequency and amplitude.
Tremors may affect the head, limbs or whole body. They occur while the patient is awake and should disappear during sleep. If the movement continues during sleep, it’s worth reconsidering whether you’re actually looking at a tremor.
Rather than immediately trying to name the disease, it can be more useful to ask when the tremor occurs.
Does it happen when the animal is standing still?
This suggests a postural tremor.
One striking example is orthostatic tremor, particularly described in giant-breed dogs. These dogs tremble dramatically while standing, but the tremor disappears when they walk, sit or lie down.
Idiopathic head tremor syndrome is another familiar example. Dogs develop repetitive vertical or horizontal movements of the head but remain completely normal between episodes. The movement will often disappear when the dog is distracted or lies down. Despite how alarming it can look, this is usually a benign condition.
Does it appear or worsen with purposeful movement?
Think intention tremor.
These tremors typically become more obvious when an animal attempts a purposeful action and usually point us towards the cerebellum and its associated pathways.
Look for the company the tremor keeps: cerebellar ataxia, hypermetria, truncal sway, menace deficits despite normal vision, nystagmus or occasionally a head tilt.
The important caveat is that not every patient with cerebellar disease has an intention tremor. Its absence certainly doesn’t rule cerebellar disease out.
And what is a twitch?
This is where things become particularly useful.
Unlike the regular oscillation of a tremor, a twitch is irregular. Its frequency and amplitude vary rather than following a repetitive rhythm.
These movements can arise from peripheral nerve hyperexcitability, where motor nerves fire abnormally. Depending on their appearance and severity, we may describe them as fasciculations, myokymia, neuromyotonia, cramps or tetany.
Some descriptions are particularly helpful:
Fasciculations – small, brief contractions producing a flicker beneath the skin.
Myokymia – continuous rippling muscle activity, sometimes producing the characteristic “bag of worms” appearance beneath the skin.
Neuromyotonia – continuous muscle activity associated with stiffness and delayed relaxation.
Cramps – sudden involuntary muscle contractions that may be painful.
Tetany – intermittent sustained muscular contractions, commonly associated with increased neuronal excitability such as that produced by hypocalcaemia.
Why does the distinction matter?
Because a twitch sends us down a very different diagnostic path from a true tremor.
An irregularly twitching patient should make us think about problems such as:
- electrolyte abnormalities, particularly hypocalcaemia
- endocrine disease
- toxicity
- neuromuscular disease
- motor neuron disease
- hereditary channelopathies.
A wide variety of toxicities can produce peripheral nerve hyperexcitability and generalised fasciculations or tetany. The original review includes pyrethrins, metaldehyde, mycotoxins, organophosphates, chocolate and caffeine among the reported possibilities.
So, the dog that comes into the clinic “tremoring” after a possible toxin exposure may not be demonstrating a tremor at all.
Don’t forget the patient around the movement
As ever in neurology, don’t diagnose the video before you’ve examined the patient.
Pain, weakness and musculoskeletal disease can all result in shaking. Cardiovascular, respiratory and metabolic abnormalities may also mimic neurological movement disorders.
Then look at the rest of the neurological examination.
A young dog with a generalised tremor but otherwise relatively normal examination presents a very different problem from a dog with an intention tremor, hypermetria and a menace deficit, or a weak dog with muscle atrophy and fasciculations.
The involuntary movement is a clinical sign. The rest of the patient gives it context.
One simple movement tip
When faced with an animal that is shaking, don’t begin by asking:
“What causes tremors?”
Start by watching carefully and asking:
“Is this movement regular or irregular?”
Regular and rhythmic → think tremor.
Irregular and variable → think twitch/peripheral nerve hyperexcitability.
It’s a small distinction, but one that can completely change your diagnostic approach.
At Movement Referrals, we believe good neurology starts before the MRI scanner. Careful observation, accurate description and localisation remain some of the most powerful diagnostic tools we have.
Because when it comes to tremors and twitches, the movement matters.