SYMPTOM
Shaking or trembling
Involuntary shaking or trembling of part or all of the body, ranging from shivering with cold or fear to tremors with no obvious trigger.
Pain
Trembling and shaking are among the more visible manifestations of pain in companion animals, reflecting both the physiological stress response and the muscular tension that accompanies discomfort. Pain-related trembling may be localised to specific body regions or may be generalised depending on the source and severity. Animals experiencing acute pain may tremble more intensely than those with chronic discomfort, though persistent low-grade trembling can also accompany long-standing painful conditions.
Fear and Anxiety
The autonomic nervous system response to fear and anxiety produces a cascade of physiological changes that can include visible trembling or shaking. This response involves adrenaline release, increased muscle tension, and sympathetic nervous system activation that collectively produce involuntary muscle movements. The trembling may be triggered by identifiable stimuli such as loud noises, unfamiliar environments, or veterinary visits, or may occur in response to more diffuse anxiety that lacks an obvious trigger.
Neurological
Tremors originating from neurological conditions may differ in character from pain or fear-related shaking, sometimes presenting as rhythmic, repetitive movements that affect specific body regions or the entire body. Cerebellar disease, certain storage diseases, inflammatory brain conditions, and degenerative neurological processes can all produce tremor as a primary or accompanying sign. The specific pattern of the tremor (its frequency, its distribution, and whether it occurs at rest or during movement) can sometimes provide information about which neurological structures are involved.
Metabolic
Significant metabolic disturbances can produce trembling or shaking through effects on muscle and nerve function. Hypoglycaemia is a well-recognised cause of trembling: falling blood glucose activates the sympathetic nervous system, which produces muscle tremors, and because nervous tissue depends on glucose for energy, a continued fall can lead to dullness, collapse, seizures and coma. Hypocalcaemia, electrolyte imbalances, and certain endocrine disorders can similarly affect neuromuscular function and produce visible trembling. These metabolically driven tremors may occur in specific contexts: after fasting, during periods of high energy demand, or in association with other systemic illness.
Toxic Exposure
Various toxic substances can produce neuromuscular signs including trembling, shaking, and muscle fasciculations. Exposure to certain pesticides, chemicals, plants, medications, and recreational drugs can disrupt normal nerve-muscle communication or directly affect the nervous system. Toxin-related trembling can begin within minutes to hours of exposure, although onset is delayed with some substances, and it can progress to seizures, raised body temperature, coma and death. How much has been absorbed, and how far the signs will go, cannot be judged from the trembling itself.
Cold and Thermoregulatory
Shivering is a normal physiological response to cold that generates heat through rapid muscle contractions. Small dogs, lean dogs, and breeds with thin coats are particularly susceptible to cold-induced shivering. While normal thermoregulatory shivering resolves once the animal warms up, persistent shivering in warm environments or shivering that seems disproportionate to the ambient temperature may suggest other contributing factors.
Why timing matters
Early observation
Occasional trembling in specific, identifiable contexts, such as during thunderstorms or at the veterinary clinic, may represent situational responses that resolve when the triggering context passes. Early episodes that are clearly linked to identifiable triggers and resolve promptly may provide less cause for concern than trembling that occurs without apparent provocation. A first episode with no trigger is different: appearance alone cannot separate a fear response from low blood glucose, low blood calcium or a toxin, which are identified from blood tests and the history of exposure.
Later presentation
Trembling that becomes more frequent, occurs in a wider range of contexts, or develops without identifiable triggers may suggest a changing underlying picture. Animals that previously only trembled during storms may begin trembling at any loud noise, or trembling that was previously confined to the limbs may spread to involve the whole body. Changes in the character of the trembling (from fine tremors to coarser shaking, or from intermittent to continuous) can also be informative.
Different causes of trembling follow different temporal patterns. Anxiety-related trembling may wax and wane with environmental stressors and may be influenced by seasonal factors such as the fireworks season. Pain-related trembling may gradually increase in frequency and intensity as an underlying painful condition progresses. Neurological tremors may show a slowly progressive course or may remain relatively stable. Metabolic causes may produce episodic trembling that correlates with fluctuations in the relevant metabolic parameter. Toxic causes, and acute metabolic causes such as low blood glucose and low blood calcium, are the exception: they progress over hours, not weeks, and tremors can be followed by seizures, coma and death.
Conditions commonly associated
Addisons Disease in Dogs
Addison's disease can cause trembling because insufficient cortisol and aldosterone disrupt electrolyte balance and the body's normal stress response, and shaking, shivering or tremors are reported in about 17% to 27% of affected dogs. Signs can wax and wane and are typically brought on or worsened by stress, and some dogs develop an Addisonian crisis, a life-threatening state of low blood volume and low blood pressure.
Noise Phobia in Dogs
Trembling is a hallmark fear response in dogs with noise phobia, often occurring alongside other signs of distress during exposure to triggering sounds.
Epilepsy in Dogs
Trembling may occur during the post-ictal period following seizures, or as part of focal seizure activity affecting motor control centres.
Syringomyelia (CM/SM)
Shaking or trembling may occur in CM/SM dogs, possibly related to pain or neurological involvement.
Noise Phobias
Noise phobias trigger involuntary shaking as part of the physiological fear response.
Syringomyelia
Pain-related trembling may occur in dogs with symptomatic syringomyelia.
Phaeochromocytoma in Dogs
Episodic hormone surges from this tumour can produce sudden trembling as the body responds to the adrenaline spike.
Cerebellar Hypoplasia
Reaching for food or attempting a precise movement often triggers a characteristic head and body tremor in animals with cerebellar hypoplasia.
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Chocolate Toxicity in Dogs
Methylxanthines in chocolate overstimulate the nervous system. Signs usually appear within 6 to 12 hours of ingestion, and restlessness and vomiting can progress to tremors, seizures and abnormal heart rhythms.
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Fear Aggression in Dogs
Trembling in the presence of a feared trigger reflects the same underlying anxiety that can tip over into defensive aggression.
Generalised Anxiety in Dogs
Trembling even without an obvious trigger is common in dogs whose baseline anxiety runs high with this condition.
Idiopathic Generalised Tremor Syndrome
This condition produces a fine, continuous whole-body tremor that is usually the first and most obvious thing noticed.
Idiopathic Head Tremors
Episodes involve a fine, repetitive tremor confined to the head, often a side-to-side or up-and-down nodding motion, while full alertness is maintained throughout.
Permethrin Toxicity in Cats
This insecticide overstimulates nerve and muscle activity. Tremors and muscle twitching usually start within a few hours of exposure but can be delayed for up to 72 hours, and can progress to seizures and death.
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Phaeochromocytoma
The same hormone surges that raise heart rate and blood pressure can also produce visible trembling episodes.
Phobia of Vehicles in Dogs
Fear of the vehicle itself can produce visible trembling in the run-up to or during a journey.
Xylitol Toxicity in Dogs
Xylitol triggers a surge of insulin that drives blood sugar down sharply. Signs of low blood sugar, which can include trembling alongside vomiting, weakness and wobbliness, can develop within 30 minutes of ingestion or be delayed for up to 12 to 18 hours, and can progress to seizures and coma.
Insulinoma
Low blood glucose caused by this insulin-secreting tumour can produce episodes of muscle tremors, weakness or collapse, typically after fasting, exercise or excitement, and episodes can progress to seizures.
Eclampsia in Dogs
Eclampsia produces trembling or muscle tremors when blood calcium levels drop rapidly, most often two to three weeks after whelping in small-breed dogs nursing large litters. It is an acute, life-threatening condition: panting and restlessness are followed by tremors, twitching and changes in gait, and then by sustained muscle spasm, seizures, coma and death if calcium is not restored.
Hepatic Encephalopathy
Hepatic encephalopathy develops when toxins that the liver would normally filter begin to affect the brain. Fine tremors are a rare sign, described in chronic recurrent cases. The more typical signs are changes in behaviour, aimless wandering, head pressing and poor coordination, which tend to come in episodes and can progress to seizures and coma.
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When to explore further
Trembling or shaking that occurs at rest in a warm environment without any apparent emotional trigger may suggest a physiological cause rather than a behavioural response. The absence of identifiable external triggers distinguishes this pattern from fear or cold-related trembling and may point towards pain, metabolic, or neurological contributing factors.
Trembling that is accompanied by other signs of illness such as lethargy, appetite changes, vomiting, diarrhoea, or changes in urination may suggest that the shaking is part of a broader systemic process. The combination of trembling with these additional signs provides a more complete picture than the trembling alone.
Progressive worsening of trembling over days to weeks, particularly if it develops from intermittent to persistent or from localised to generalised, may indicate an evolving condition. The trajectory of change can be as informative as the current severity of the trembling.
Trembling that develops acutely and is accompanied by other neurological signs such as loss of balance, head tilting, abnormal eye movements, or altered consciousness may reflect a toxin, a metabolic disturbance such as low blood glucose or low blood calcium, or a neurological event. In the toxic and metabolic causes, tremors can be followed by seizures and coma within hours.
Trembling in a toy-breed puppy under six months of age, after a missed meal, stress or prolonged play, may reflect juvenile hypoglycaemia. Low blood glucose in a puppy can move from trembling and dullness to collapse, seizures and coma, and recovery after feeding does not rule it out.
Where trembling recurs in an animal that is otherwise bright and behaving normally, recording the episodes (when they occur, how long they last, what seemed to precede them, and what brought relief) helps identify patterns that may not be apparent from individual events. Video recordings are particularly valuable as they capture the character, distribution, and intensity of the trembling in a way that verbal descriptions often cannot. Noting whether the trembling occurs at rest or during specific movements, whether it affects particular body regions or the whole body, and whether it can be stopped by touching or repositioning the animal all provide useful clinical details that can help characterise the nature of the trembling.
Last reviewed: 9 October 2026 · Dr Alastair Greenway MRCVS