Destruction of the upper motor neurons in the left lateral pathway results in loss of

Right side's movement

Explanation:

The left lateral side of the brain is responsible for the movement of the right side

There is a primary motor cortex that is responsible for the movement of right side of the body. The sensation produced in right limb cross to the other side and causes movement of the left side or vice versa. In such case destruction of the upper motor neurons in the left lateral pathway results in loss of Right side's movement