Rodrigo Gutierrez‐Quintana

Background Although idiopathic episodic head tremor (IEHT) in dogs is well‐known, little is known about structural brain lesions causing structural episodic head tremor (SEHT). Hypothesis/Objectives Describe 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. Animals One hundred dogs with IEHT (n = 71) or SEHT (n = 29). Methods Retrospective, multicenter, study of dogs with episodic (nonintentional) head tremor and brain MRI between 2004 and 2022. Results Lesions 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 Importance Presence 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.

Case Description A 9‐month‐old intact male domestic shorthair cat was evaluated for increasing frequency of generalized tonic‐clonic seizures. Clinical Findings The cat was reported to have had episodes of circling between the seizures. Upon examination, the cat had bilateral inconsistent menace response but otherwise normal physical and neurological examinations. Diagnostics Magnetic resonance imaging (MRI) of the brain identified multifocal, small, rounded intra‐axial lesions within the subcortical white matter containing fluid with similar characteristics as cerebrospinal fluid. Evaluation of urine organic acids showed increased excretion of 2‐hydroxyglutaric acid. An XM_023255678.2:c.397C>T nonsense variant in the L2HGDH gene encoding L‐2‐hydroxyglutarate dehydrogenase was identified using whole genome sequencing. Treatment and Outcome Levetiracetam treatment was initiated at 20 mg/kg PO q8h, but the cat died after a seizure 10 days later. Clinical Relevance We report the second pathogenic gene variant in L‐2‐hydroxyglutaric aciduria in cats and describe for the first time multicystic cerebral lesions on MRI.