Abstract: Background: Although episodic head tremor (EHT) is a clinical sign of idiopathic head tremor syndrome (IHTS), there is little known about structural brain abnormalities that can cause structural EHT (SHTS).
Hypothesis/Objectives: To describe signalment, semiology, MRI findings and outcome of dogs with EHT. We hypothesized that dogs with lesions affecting the middle cranial fossa, including third ventricle, or mesencephalic aqueduct could manifest SHTS semiology.
Animals: 100 client-owned dogs with IHTS (n=72) or SHTS (n=28) that underwent MRI of the head.
Methods: Observational retrospective, multi-center, study between 2010-2021.
Results: All 100 dogs had a non-intentional isolated EHT. Lesions on MRI in SHTS dogs were localized to the middle cranial fossa (15/28), cerebrocortex (4/28), brainstem (2/28) or were multifocal (7/28) with involvement of the thalamus (5/7). Compression of the mesencephalic aqueduct (18/28) or third ventricle and/or the interthalamic adhesion (14/28) was present. Dogs with SHTS had more likely additional neurological signs and were older at onset of clinical signs and presentation than dogs with IHTS (p< 0.001 for both). Dogs with SHTS were more likely to be euthanized at the time of diagnosis (p< 0.001). Many dogs with IHTS received no treatment (41/72). In 80% of dogs with IHTS, EHT episodes decreased more than 50% or completely abated. In SHTS dogs treated for an underlying meningoencephalitis, EHT remission occurred.
Conclusions and clinical importance: Presence of other neurological signs and older age might indicate an underlying structural cause for EHT. EHT might be associated with lesions affecting the mesencephalic aqueduct, third ventricle or interthalamic adhesion.
