Idiopathic Head Tremor Syndrome (IHTS) in dogs, also known as episodic head tremor syndrome or idiopathic head tremors, is a fascinating yet benign neurological condition. For dog owners, witnessing their beloved pet’s head involuntarily shake can be alarming, often leading to concerns about serious underlying issues like seizures. However, understanding IHTS is crucial, as it typically presents a much different, more reassuring prognosis and management approach compared to other neurological disorders. This guide aims to provide a thorough overview of IHTS, helping owners recognize the signs, understand the diagnosis, and differentiate it from more severe conditions.
What is Idiopathic Head Tremor Syndrome (IHTS)?
Idiopathic Head Tremor Syndrome is characterized by involuntary, focal head tremors in an otherwise normal and alert dog. The term “idiopathic” signifies that the exact cause of these tremors is currently unknown. While rare anecdotal reports suggest similar signs in cats, IHTS has primarily been documented and studied in dogs.
Certain breeds appear to have a higher predisposition to IHTS. English Bulldogs are classic examples, accounting for approximately 37% of reported cases, followed by Doberman Pinschers at 8%. However, it’s important to note that any dog breed, including mixed breeds, can be affected. The majority of dogs (around 88%) experience their first head tremor episode before the age of four, though the onset can range widely from three months to twelve years. Bulldogs, in particular, tend to have a younger average age of onset, typically around two years, compared to an average of nearly three years for other breeds.
Recognizing the Signs: What IHTS Looks Like
The hallmark clinical sign of IHTS is a distinct focal head tremor that occurs while the dog is awake, dozing, or resting. These tremors are not typically associated with other neurological deficits, meaning the dog’s overall behavior, awareness, and mobility remain unaffected during an episode.
The head tremors commonly manifest in two main patterns:
- Vertical “Yes” Movement: The head bobs up and down, similar to a human nodding agreement.
- Horizontal “No” Movement: More frequently observed, the head shakes from side to side, resembling a human shaking their head “no.”
While less common, some cases (up to 15%) may also include a rotational component to the head movement. The intensity and frequency of these tremor episodes can vary significantly, even within the same dog. An individual dog might experience varying amplitudes and frequencies of tremors from one episode to the next, or even during a single episode, though the direction of the tremor usually remains consistent throughout a single event.
A serious-looking Bulldog, a breed commonly affected by idiopathic head tremor syndrome, resting
Most tremor episodes associated with IHTS are brief, lasting less than five minutes in the majority of dogs. However, about 15% of affected dogs may experience episodes that extend up to an hour, and there are even rare accounts of continuous head tremors lasting over twelve hours. The frequency of episodes also varies greatly, from several times a day or week to as infrequently as once every three to four months. A key characteristic that helps differentiate IHTS from other conditions is that affected dogs remain alert, mobile, and responsive throughout the tremor episodes. While a small percentage of dogs might appear slightly agitated, nervous, or lethargic during an episode, there are no notable autonomic signs such as excessive drooling (hypersalivation), involuntary urination, or defecation.
The Unique “Distraction” Factor
One of the most distinctive and useful clinical features for identifying IHTS is the ability to “distract” a dog out of an episode. Up to 87% of dogs with IHTS can be temporarily brought out of their head tremor by drawing their attention elsewhere. This can be achieved by:
- Calling their name
- Offering a favorite treat
- Presenting a stimulating toy
- Engaging them in play
This “distractibility” is a critical clue for veterinarians, as it is uncommon in other types of tremors or seizure activity and often provides sufficient evidence for a confident clinical diagnosis.
Differentiating IHTS from Other Conditions
It’s crucial for veterinarians to differentiate IHTS from other conditions that might present with similar signs, particularly focal seizures, which carry a much different diagnostic and treatment pathway.
- Focal Seizures: Unlike IHTS, focal seizures often involve autonomic signs (like salivation, urination), are typically not interruptible by distraction, and do not respond to conventional anti-epileptic medications. Dogs experiencing focal seizures may also exhibit altered consciousness or post-ictal (after seizure) confusion, which is absent in IHTS.
- Other Tremors and Movement Disorders: Tremors caused by toxins (e.g., pyrethrins, metronidazole, mycotoxins) or other movement disorders (like essential tremor syndrome, cervical dystonia, paroxysmal dyskinesia) are usually not episodic and don’t typically affect only the head in isolation.
- Intention Tremor: This type of tremor, often linked to underlying cerebellar disease, is triggered by goal-oriented movements (e.g., reaching for food) and generally does not occur at rest or in a neutral head position. This contrasts sharply with IHTS, where tremors can occur during rest or when dozings.
Diagnosis: How Veterinarians Confirm IHTS
Diagnosing IHTS is primarily a clinical process, meaning it’s based on observing the classic focal head tremors and ruling out other neurological conditions. There is no specific diagnostic test for IHTS. A thorough neurological examination performed by a veterinarian on an affected dog will typically yield normal results.
Even advanced diagnostic evaluations, such as comprehensive blood work (hematology, biochemistry, urinalysis, liver function, thyroid hormone testing), cervical and brain MRI, cerebrospinal fluid analysis, neurometabolic screening, PCR testing for canine distemper virus, and electrodiagnostic evaluation, have shown normal findings in dogs with IHTS.
Therefore, the most valuable tool for confirming IHTS is the owner’s observation of the “distractibility” feature. Veterinarians often instruct owners to attempt to distract their pet during an episode. If this consistently halts the tremor, coupled with a consistent clinical history and normal examination findings, it is often enough to establish a confident clinical diagnosis without the need for extensive and costly advanced imaging or other tests.
Understanding the Causes: Theories Behind IHTS
While the exact cause remains unknown, several theories have been proposed. One leading theory suggests that IHTS involves abnormalities in the stretch reflex mechanisms within the neck muscles. This could lead to an alternating pattern of contraction and relaxation in these muscles, resulting in the tremor. This hypothesis is supported by the normal findings in advanced imaging, CSF analysis, and even post-mortem examinations of affected dogs, as well as the observation that a change in head or neck position can momentarily stop the tremor.
Interestingly, research into Doberman Pinschers with IHTS has suggested a genetic component. Pedigree analysis of affected Dobermans traced the condition back to a single sire, strongly indicating an inherited episodic head tremor syndrome within this particular breed. This highlights the potential for genetic factors in specific breed lines.
Treatment and Prognosis: A Reassuring Outlook
One of the most reassuring aspects of IHTS for dog owners is its benign nature and favorable prognosis. Currently, there is no evidence that any attempted treatments—including anti-seizure medications (such as phenobarbital, potassium/sodium bromide, diazepam), clonazepam, calcium carbonate, corticosteroids, or supplements (like fish oil)—lead to significant improvement in clinical signs. Consequently, treatment for IHTS is generally not indicated, as the condition is not harmful to the dog.
Dogs diagnosed with IHTS are otherwise healthy and are not expected to develop any other neurological or health problems directly related to this syndrome. Furthermore, approximately two-thirds of affected dogs will experience a spontaneous improvement in the severity or frequency of episodes, or even a complete resolution of the tremors over time. Critically, there have been no reported cases of dogs dying or being euthanized as a direct result of IHTS.
In summary, IHTS is a benign condition characterized by focal head tremors in dogs. While it can be concerning for pet parents to witness, affected dogs typically do not require treatment, and the condition does not progress to other neurological deficits. Often, the tremors will spontaneously regress over time. Being aware of IHTS is vital, as it prevents misdiagnosis as focal seizures, which involve a more intensive diagnostic work-up, different treatment recommendations, and a distinct prognosis. [Internal Link: Common Dog Health Concerns] [Internal Link: When to Call the Vet: Understanding Dog Symptoms]
References
- Guevar J, De Decker S, Van Ham LML, et al. Idiopathic head tremor in English Bulldogs. Movement Disorders. (2014). 2: 191 – 194.
- Lowrie M, Garosi L. Classification of involuntary movements in dogs: tremors and twitches. Vet J. (2016). 214: 109 – 116.
- Shell LG, Berezowski J, Rishniw M, et al. Clinical and breed characteristics of idiopathic head tremor syndrome in 291 dogs: a retrospective study. Vet Med Internat. (2015). dx.doi.org/10.1155/2015/1645463
- Wolf M, Bruehschwein A, Sauter-Louis C, et al. An inherited episodic head tremor syndrome in Doberman Pinscher dogs. Movement Disorders. (2011). 23: 2381 – 2386.
