Rusty came to us due to a several day history of poor appetite and lethargy. He had a very enlarged lymph node under his jaw, and his blood work showed very high calcium levels. First on our list of likely diseases was, unfortunately, a type of cancer called lymphoma. We prepared his owner for some likely bad news, but we did the tests to confirm the potential diagnosis- a sample of the enlarged node looking for cancer cells. We put Rusty on some supportive care with IV fluids while we awaited the results. While we waited, the doctor noticed the calcium levels dropped well while on fluids- better than usual. She also noticed some subtle changes in potassium and sodium that were unusual for a pet on IV fluids. Could he be an atypical case of Addison's disease? The next day, test results came back- no cancer cells seen, only inflammation! A test went out for Addison's disease, and some initial treatment started. And guess what- Rusty got better! His lymph node shrank and he started eating again. Sure enough.... Testing confirmed Addison's disease- a disease also known as "the great pretender" due to the many presentations that can occur. Rusty has a good prognosis and is a happy boy again. What a great case to show the importance of doing appropriate testing and not making assumptions in medicine. Thank you to Rusty's owner, who let us do everything we needed to help this sweet boy. We are happy every time we see him!!