Backstory - sister-in-law's horse, 17 year old gelding, been in the same pasture since he was 2 years old. Semi-retired due to dropped hind pasterns, but still active and very healthy. He presented with sudden onset leg swelling and ventral edema. Was literally fine in the morning and was so swollen by that evening that his skin was splitting. Took to the university and was diagnosed with kidney failure/injury. He's been there for 4 days and still no answers and not much improvement. They have done multiple scans looking for tumors and nothing. Lungs and heart look normal. Kidneys are in bad shape. Labs are showing high white blood count and high creatinine. He's been getting fluids, Lasix, antibiotics and they've started him on steroids today. Fever was present but went down after antibiotics were started. Vets are thinking he may have ingested something toxic.   

Anybody ever dealt with something similar?They are waiting to see if the steroids make a difference but after that they are basically out of options.  

With the suddeness of the symptoms I would agree.  Check his pasture closely for toxic weeds.  Check Feed and Hay as well.

Hows he doing?