Idiopathic and structural episodic nonintentional head tremor in dogs: 100 cases (2004‐2022)

Abstract

BackgroundAlthough idiopathic episodic head tremor (IEHT) in dogs is well‐known, little is known about structural brain lesions causing structural episodic head tremor (SEHT).Hypothesis/ObjectivesDescribe semiology, magnetic resonance imaging (MRI) findings and outcome of dogs with IEHT or SEHT. We hypothesized that structural lesions affecting the middle cranial fossa or mesencephalic aqueduct could lead to SEHT.AnimalsOne hundred dogs with IEHT (n = 71) or SEHT (n = 29).MethodsRetrospective, multicenter, study of dogs with episodic (nonintentional) head tremor and brain MRI between 2004 and 2022.ResultsLesions on MRI in SEHT dogs were localized to the middle cranial fossa (15/29), cerebrocortex (3/29), brainstem (2/29), fourth ventricle (1/29) or multifocal (8/29) with thalamus involvement (6/8). Secondary compression of the mesencephalic aqueduct (19/29), third ventricle or interthalamic adhesion or both (14/29) was common. The most common underlying condition in dogs with SEHT was a pituitary mass. Dogs with SEHT were older, had additional neurological signs and were more likely to be euthanized after diagnosis (P < .001 for all) compared to IEHT dogs. Two SEHT dogs had only tremor. In IEHT dogs, 8/10 owners reported that the tremor decreased or abated over time (range, 106‐2315 days) without treatment. Tremor remission occurred in SEHT dogs treated for underlying meningoencephalitis.Conclusions and Clinical ImportancePresence of additional neurological signs and older age may indicate an underlying structural cause for episodic (nonintentional) head tremor involving the mesencephalic aqueduct, third ventricle, interthalamic adhesion or some combination of these. An intracranial structural abnormality cannot be excluded in dogs with normal neurological examination.

Medial strabismus (esotropia) at rest associated with contralateral paramedian thalamic ischemic infarction in 2 dogs

“…Finally, dog 1 manifested an episodic head tremor that had an acute onset along with the other neurological signs and ceased as soon as the dog improved neurologically. Structural episodic nonintentional head tremor in dogs has been associated with lesions in the thalamus, including the interthalamic adhesion and third ventricle, or mesencephalic aqueduct 18 . Although its pathogenesis is unknown, it has been speculated that third ventricular cerebrospinal fluid flow imbalance or a compressive mass at that level might lead to an increase in the pressure effect and subsequent distortion of the dorsomedial red nucleus and dentatorubrothalamic pathways 19 .…”

“…Although its pathogenesis is unknown, it has been speculated that third ventricular cerebrospinal fluid flow imbalance or a compressive mass at that level might lead to an increase in the pressure effect and subsequent distortion of the dorsomedial red nucleus and dentatorubrothalamic pathways 19 . In a recent study, there were no cases with a focal lesion such as a cerebrovascular accident 18 . Our case indicates that a more specific region (ie, paramedian thalamus) might be associated with the manifestation of structural episodic nonintentional head tremor.…”