A patient is unable to move his right arm or leg

A patient is unable to move his right arm or leg. When asked to smile, the left side of his mouth droops. Where is the lesion?

1.Left motor cortex
2.Right motor cortex
3.Left brainstem
4.Right brainstem
5.Cervical spine

View explanation

It is useful to divide the body into the areas such as: face/arms/legs, left/ right, proximal/distal. This allows a rapid diagnosis of where the lesion might be. This patient shows crossed signs. The left side of the face is affected but so is the right side of his body. Therefore, if the lesion were cortical, there would have to be two lesions to explain this (A and B). As his face is involved, there has to be a lesion above the spinal cord (E). Crossed signs tend to suggest brainstem involvement (if only one lesion is responsible). In this case a left brainstem lesion © would affect cranial nerves exiting on that side (LMN left-sided droop) and the cortical spinal tracts as they descend which then go on to cross at the medulla (UMN right arm and leg weakness). A right brainstem (D) lesion would cause the opposite. Please note that this is a general rule of thumb and lesions do not always result in textbook deficits.