Simple SummaryCerebral salt wasting syndrome is defined as a hyponatremic condition due to sodium loss through the kidney during intracranial disorders. A 12-year-old spayed female domestic shorthair cat was referred to our referral animal hospital with tetraplegia and a history of hyponatremia with dehydration from a local hospital after intravenous fluid treatment. The cat was suspected to have intracranial disease after a thorough physical and neurologic examination. MRI revealed bilateral parietal lobe cerebrocortical gray-white matter junction T2/Flair high signal related to rapid electrolyte calibration, and C2 spinal cord ventral area T2 high signal indicated ischemic myelopathy. After 2 days, the cat revisited our hospital with severe lethargy and anorexia. Laboratory examination revealed hyponatremia (136 mEq/L) with dehydration. Through history-taking, laboratory examination, imaging, and fluid therapeutic response, the cerebral salt wasting syndrome was tentatively diagnosed. Electrolytes stabilized after starting treatment with fludrocortisone, and the cat was discharged. After 3 weeks, MRI revealed that the parietal lobe lesion had disappeared; however, the spinal cord ischemic lesion got worse than previous imaging, and the cat was euthanized. This is the first case of suspected cerebral salt-wasting syndrome in a cat. And this syndrome might be included on the differential diagnosis list for cats with intracranial disease, dehydration, and hyponatremia.AbstractA 12-year-old spayed female domestic short cat was presented with tetraplegia. The cat also showed signs of hyponatremia and dehydration, which were rapidly corrected by intravenous fluid infusion. Based on thorough physical and neurological examinations, the patient was suspected of having an intracranial disease. MRI revealed a high-signal T2 image of the bilateral parietal cerebral cortical gray matter junction, which is associated with fast electrolyte calibration, and a high-signal T2 image of the C2 spinal cord ventral area, which is associated with ischemic myelopathy. The cat reappeared three days later due to anorexia. Laboratory examinations revealed that the cat was clinically dehydrated and exhibited hyponatremia. Other causes of hyponatremia were excluded through history-taking, laboratory examination, imaging, and therapeutic response to fluid therapy, except for cerebral salt-wasting syndrome (CSWS). The cat was discharged 3 days after the start of fludrocortisone therapy with electrolytes within the normal range. Magnetic resonance imaging (MRI) was performed again 1 month after hospitalization, and the cerebral lesion disappeared, but the spinal cord lesion worsened compared to the previous image. The patient was euthanized due to the progression of the spinal lesion, with a poor prognosis and poor quality of life. This is the first case of suspected CSWS with a cervical spinal lesion in a cat.