Kelli Grant's cat Max had always loved to eat but that was nothing compared to how ravenous he became a few years ago, howling and pestering her for food.

Cats demolishing cardboard packaging to get to what was inside, opening cupboards, devouring the dog's food and "stealing the lamb roast" from the table – and still losing weight. These are the characteristics of large numbers of older cats with hyperthyroidism, according to vet Anne Fawcett from Sydney Animal Hospitals Inner West in Stanmore.

Vet Lara Boland, right, and veterinary nurse Tiffany Formosa with one of their patients. Credit:Janie Barrett

In Chippendale, Kate Webb's cat Patrick, nicknamed Pat the Fat Cat, always had a huge appetite, yet nobody noticed he was losing weight. On a visit home, her grown-up son asked: "What are you doing, starving Patty?"

It was only when Pat developed a rash that a vet discovered a tumour on his thyroid, and problems with his heart – signs that he had advanced hyperthyroidism. Ms Grant, from Marsfield, discovered her cat Max also had hyperthyroidism when she took him to the Cat Palace in Chatswood.