History and Clinical Findings
3 year female spayed domestic medium hair cat presented for not eating or drinking in the last 24 hours, and seeming ataxic at home. The owner was gone over the weekend and returned to find the cat lethargic, hyporexic and seemingly hugging the wall. Vaccination status is up-to-date and she receives Frontline for flea and tick prevention. She is usually an indoor cat, but got out two months ago and was gone for two days.
Findings Mentation: Dull
Posture and gait: Ambulatory tetraparesis with wide base stance more in the pelvic limbs compared to the thoracic limb. Low head carriage with a crouched stance. Not able to maintain balance and falls down with splayed legs in all fours.
Cranial nerve examination: Mildly anisocoria (mild miosis noted on the right eye). Very mild right sided head tilt after examining. No resting nystagmus, but when placed in dorsal recumbency, would have couple beats of vertical nystagmus, and then later noted a rotary nystagmus fast phase to the left. Physiological nystagmus was not easy to elicit until when picked up and swung around
Conscious proprioception/postural reactions: Normal paw placement in the thoracic limbs, and occasionally delayed on the left pelvic limb. Slightly decreased hopping in both left thoracic and pelvic limb compared to the right side. Mainly normal hopping on the right side. Normal thrust and withdrawals.
Limb reflexes (myotatic and flexor withdrawals): Normal withdrawals and patellar reflexes. Perineal reflex and tail tone: Normal
Cutaneous trunci: Cannot elicit
Superficial/Deep pain: Normal
Spinal hyperesthesia: Negative.
Neuroanatomical localization: Central vestibular (left side – paradoxical)
The rest of the physical examination findings was unremarkable. Bloodwork and thoracic radiographs were unremarkable.
MRI of the neurocranium using standard sequences. Post-contrast images acquired in transverse, sagittal, and dorsal planes following administration of 0.1 mmol/kg gadopentetate dimeglumine. Additional transverse T2W and pre-contrast T1W images acquired of the cranial cervical spinal cord. White matter of the cerebral hemispheres, internal capsule, corpus callosum, arbor vitae of the cerebellum, and pyramids of the medulla oblongata are diffusely and bilaterally symmetrically T2W and FLAIR hyperintense (relative to gray matter) and T1W hypointense with no contrast enhancement. Cavities of both olfactory bulbs are mildly dilated. Patchy T2W subtly hyperintense, T1W iso- to subtly hypointense signal is present within the white matter at the lateral aspects of the cranial cervical spinal cord.
Summarized Imaging Diagnosis:
Diffuse, bilaterally symmetric, cerebral, cerebellar, and cranial cervical spinal cord white matter lesions without contrast enhancement – most likely toxic encephalomyelopathy such as bromethalin toxicosis. Other less likely differential diagnoses include metabolic encephalomyelopathy or diffuse leukoencephalitis.
Histopathological findings: Diffusely the white matter is irregularly distended by numerous large colorless vacuoles that cavitate and fuse to become large open spaces (spongiosis). Spongiosis is most severe in the cerebrum and cerebellum. These changes are indicative of a diffuse cerebrocortical myelinopathy, consistent with bromethalin toxicity.
Samples of brain tissue were submitted to the California Animal Health and Food Safety Lab for bromethalin toxicosis testing. Toxicology confirmed bromethalin intoxication. Brain tissue was positive for desmethylbromethalin.
Kent M, Glass EN, Boozer L et al. Correlation of MRI with the neuropathologic changes in two cats with bromethalin intoxication. 2019 J Am Anim Hosp Assoc; 55:e553-02. DOI 10.5326/JAAHA-MS-6724