When I wear high heels my middle toe goes numb, what could it be?

They might. Narrow fitting shoes or high heels can put a lot of force in the ball of the foot. This causes pinching of the interdigital nerves, and if irritated enough might lead to a neuroma. This can cause numbness, or can cause intense pain. Shoes with lower heels and have room for the toes are idea. If this persists see a podiatrist.
Toe-numbing disease. That was tongue-in-cheek answer. Thoroughly amazes me that women not only wear high heels, but walk in 'em. Certainly, they've become a symbol of feminine sex appeal, perhaps by lengthening the appearance of legs.That most women don't have some toe pain or pressure numbness-from simply changing center of gravity from arch to toes-amazes me. It seems they're weapons--used to shoot self in foot-:).