If your older cat starts losing a lot of weight despite having a ravenous appetite, the problem might be hyperthyroidism. Hyperthyroidism occurs when a cat’s thyroid gland (an organ located at the front of the neck) produces excess amounts of thyroid hormone. The problem is usually caused by a benign (noncancerous) tumor on the thyroid gland, although a small percentage of thyroid gland tumors in cats can be malignant (cancerous).
Island Bird Cat & Dog Vet Group