Pronator drift refers to a pathologic sign seen during a neurological examination.
Known as the Barré test or sign.
A positive result indicates palsy.
The sign can appear due to an upper motor neuron lesion or various other conditions, including inborn errors of metabolism, which include palsy as a symptom.
It detects mild upper limb weakness in a patient who’s awake and able to follow directions.
The patient closes their eyes, and stretches out both arms.
The shoulders joints are flexed at 90 degrees and fully extend the elbow joint.
The palms are facing up, and the patient should maintain this position for 20 to 30 seconds.
If the motor pathway is intact, the arms should remain in this position equally.
Patients with a slight weakness in one arm won’t be able to keep the affected arm raised, and ultimately the palm may begin to pronate, that is, palm facing downward.
Pronator drift is an indication of abnormal function of the corticospinal tract in the contralateral hemisphere.
The arm may remain supinated but drop lower than the unaffected arm, and the fingers and elbow might flex.
The patient is asked to hold both arms at 90 degree flexion and elbows fully extended at shoulder level in front of them, with the palms upwards, and hold the position.
If one is unable to maintain the position the result is positive.
Closing the eyes accentuates the effect: brain is deprived of visual information about the position of the body and must rely on proprioception.
Tapping on the palm of the outstretched hands can accentuate the effect.
It is a test of upper motor neuron disease.
If the forearm pronates, with or without downward motion, then pronator drift on that side reflects a contralateral pyramidal tract lesion.
With an upper motor neuron lesion, the supinator muscles in the upper limb are weaker than the pronator muscles, and as a result, the arm drifts downward and the palm turns toward the floor.
If a lesion is in the ipsilateral cerebellum or ipsilateral dorsal column, it usually produces a drift upward, along with slow pronation of the wrist and elbow.