My cat has weak hind legs but is otherwise normal, meows more, eats less—what could it be?

Weak hind legs have several common causes. 1) Leg trauma or muscle/ligament strain; 2) hind-leg fracture or arthritis; 3) neuritis, supplement vitamin B1 twice daily, two tablets each; 4) calcium deficiency from long-term unbalanced food; 5) thrombosis, mostly from heart disease blocking hind-leg arteries, with cool paw pads; 6) dry FIP, whose common symptom is hind-leg paralysis from nerve damage, sometimes with seizures. If the cat shows weak hind legs with reduced appetite, pain or screaming, see a vet promptly for a full exam and targeted treatment.