Pronator drift
Formal Definition
A bedside neurological test for upper motor neuron (corticospinal tract) weakness: the patient holds both arms extended at shoulder height with palms up and eyes closed; the affected arm gradually pronates and/or drifts downward due to contralateral hemispheric or corticospinal tract dysfunction.
How It's Used on the Ward
"Checking for drift" or "has a drift" — a quick, sensitive test for subtle hemiparesis that can be missed on direct muscle testing.
Example
""Neurology asked me to check for drift on this patient with new right-sided headache — subtle left pronator drift, maybe 10 degrees, eyes closed. Calling stroke immediately.""
Clinical Context
Pronator drift is a sensitive sign of corticospinal tract injury, often revealing weakness before formal strength testing does. A slow downward drift with pronation = upper motor neuron weakness (stroke, MS, tumor). Pure downward drift without pronation = cerebellar or sensory pathology (loss of proprioception). Check it on every neuro exam and every acute stroke suspect. Part of a full NIHSS assessment.