I'm sorry that your question wasn't answered in a timely manner. It's hard to imagine that he's terribly ill in spite of two weeks of diarrhoea if he has continued to eat and act well. I do understand that at his advanced age it's likely that I'm going to find something untoward in diagnostics but there's a good chance that these findings won't be life-threatening. I see a couple of ways forward...
The first is having a thorough physcial exam performed including diagnostics in the form of blood and urine tests. If nothing untoward is found, an abdominal ultrasound is the next diagnsotic of choice. It's particularly sensitive for evaluating the gastrointestinal tract itself. I'm mainly looking for the inflammation associated with inflammatory bowel disease (IBD) or small cell lymphoma (less likely in an otherwise normal cat).
The second is presumptively treating for IBD with either a glucocorticosteroid such as prednisolone or the antiinflammatory antibiotic metronidazole, or both. Please respond with further questions or concerns if you wish.
Thank you for your kind accept. I appreciate it. I can't set a follow-up in this venue so please return to our conversation - even after rating - with an update at your convenience. You can bookmark this page for ease of return.