9 Year old Siamese Losing weight

My 9 year old Siamese seems to be losing weight, muscle in his rear legs. His chest area seems still to be broad...His character is till the same and doesn't seem to be pained. He does at times seem to be constipated.Any ideas?

Weight loss is common in aging cats for a variety of reasons: hyperthyroid, diabetes, kidney dysfunction. When specifically losing condition in the rear, arthritis, associated nerve damage, and hip injury are also suspect.

The best thing you can do is have your cat examined by your vet, blood and urine analysis should also be included, and get a diagnosis. Some of the above conditions are easily treatable (hyperthyroid and arthritis), some are not so easy, but are still treatable (such as diabetes, kidney disease, and nerve damage)