Hemiparesis

Definition

Hemiparesis is weakness of the arm and leg on the same side of the body. The face may or may not be involved. Hemiparesis may be mild to severe. It is almost always caused by lesions involving the corticospinal tract.

Pattern of Weakness

Weakness caused by lesions of the corticospinal tract causes different muscle groups to be weakened in a particular pattern, often called predilection pattern weakness. In the upper extremity, the extensors are weaker than the flexors: the arm is held close to the body (adducted), flexed at the elbow, pronated at the forearm, and flexed at the wrist and fingers. In the lower extremity, the leg is extended at the hip, knee, and plantar flexed at the ankle.

Drift or pronator drift refers to an examination technique that can detect mild weakness in the upper extremity due to corticospinal tract lesions: with the eyes closed, the patient’s arms are extended forward from the body, parallel to the floor, palms up, activating all the muscles that...