Correlation of MRI with the Neuropathologic Changes in Two Cats with Bromethalin Intoxication

Two cats were presented with multifocal neurological signs. One cat's signs progressed over 2 wk; the other cat progressed over 5 days. Examinations were consistent with a process involving the prosencephalon, vestibular system, and general proprioceptive/upper motor neuron systems. MRI of the brain and cervical spinal cord reveal widespread T2 hyperintensity of the white matter. Affected areas included the cerebrum, cerebral peduncles, corticospinal tracts of the pons and medulla, and the cerebellum. T2 hyperintensity was present in all funiculi of the spinal cord. Diffusion-weighted imaging (DWI) and apparent diffusion coefficient (ADC) maps were consistent with cytotoxic or intramyelinic edema. Differential diagnosis included toxic or metabolic/degenerative leukoencephalopathies. Necropsies revealed widespread spongy degeneration of the central nervous system white matter. Toxicologic assays of liver specimens revealed desmethylbromethalin, a metabolite of bromethalin. Bromethalin is a rodenticide that causes uncoupling of oxidative phosphorylation. Antemortem diagnosis is challenging. DWI and ADC maps were instrumental in narrowing the differential diagnosis and raised the index of suspicion for bromethalin. Bromethalin intoxication should be considered in all animals with a progressive course of multifocal neurologic deficits. MRI, specifically, DWI and ADC maps, may serve as a biomarker of cytotoxic or intramyelinic edema associated with spongiform leukoencephalomyelopathy.