Convergence-Retraction Nystagmus in a Dog With Presumptive Ischemic Encephalopathy Following Acute Cervicothoracic Myelopathy

Convergence Retraction Nystagmus Secondary to Central Nervous System Disseminated Coccidioides Immitis Infection in a Dog

This report describes a Belgian Malinois dog residing in metropolitan Phoenix, Arizona that was presented to a veterinary neurology center with abnormal eye movements as his only clinical sign. On examination, clinical signs were isolated to convergence-retraction nystagmus. A brain MRI was performed which identified two well-demarcated, T2-hypointense and T1-isointense, avidly contrast enhancing mass lesions with moderate to severe perilesional T2 and FLAIR hyperintensity within the left frontal lobe and left dorsal midbrain. Imaging characteristics were most consistent with Coccidioides immitis fungal granulomas and serology was supportive of Coccidioidomycosis infection. The patient's clinical signs resolved quickly with antifungal and anti-inflammatory therapies, and brain granulomas were resolved or resolving on repeat imaging 10 months after initial diagnosis. To the authors' knowledge, this is the first report of convergence-retraction nystagmus secondary to an infectious etiology described in a canine patient.

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

Pseudoabducens paralysis resulting in resting medial strabismus (esotropia) is a rare consequence of a contralateral paramedian thalamic ischemic infarction in people. To date, esotropia has been reported in dogs in association with ipsilateral abducens neuropathy or extraocular myopathy, but not secondary to thalamic lesions. A 7-year-old male neutered Border Collie and a 12-year-old female neutered cross-breed dog were presented with peracute nonprogressive vestibular ataxia. Neurological examination identified right esotropia, nonambulatory tetraparesis, right head tilt, vestibular ataxia and nystagmus. Lesions in both dogs were localized to the vestibular system with thalamic involvement. Magnetic resonance imaging of the brain identified a left paramedian thalamic lacunar ischemic infarct in both dogs. Interruption of descending inhibitory pathways that decussate in the subthalamic region and innervate the contralateral motor nucleus of the oculomotor nerve leads to hypertonicity of the medial rectus. These cases indicate that esotropia is a rare but highly localizing sign in dogs with contralateral thalamic infarcts.