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What causes pleural effusion in senior cats with hyperthyroidism?

Updated On September 23rd, 2025

Pet's info: Cat | Mixed Breed | Female | spayed | 15 years old | 5.5 lbs

My 15 year old DLH spayed cat has hyperthyroidism and is on methimazole. She developed pleural effusion and tachypnea 2 days ago. She went to vet, had supportive treatments, her T4 was twice normal. She's now on 15 mg methimazole per day, lasix, and amoxicillin. Follow up ekg Tues. Cat still tachypnea but lungs clear. The vet doesn't know what caused the effusion. Any ideas?

2 Answers

Most Helpful Answer

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Answered By Megan, DVM, CVA

Veterinarian

Published on June 9th, 2017

Poor Yoda. Unfortunately there are several things that can cause pleural effusion including right sided heart failure, cancer, poor lymph drainage, certain viral infections, and more. My concern would be that she may have a heart problem or cancer because of her age and since she is still labored breathing despite no longer having pleural effusion. It may be time for her to have an ultrasound of her chest/heart. I am so sorry that you are going through this with sweet Yoda. I hope y'all are able to get her regulated with medications and figure out what is going on with her.

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Other Answers

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    Answered By Lindsey Edwards MVB, BSc, IVCA

    Veterinarian

    Published on

    Poor Yoda, unfortunately in older cats the prognosis for cats with recurrent pleural effusion is quite poor. A sample of the fluid can be tested and examined under the microscope for indications as to the underlying nature but cancer is a common cause and should be ruled out in cases which return so quickly

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