Distinguishing between extrinsic and intrinsic tongue muscle weakness in unilateral hypoglossal palsy

Abstract

A 53-year-old man presented with multiple right cranial nerve palsies that included the tongue. When the tongue was protruded, it deviated to the right. However, when the tongue was not protruded, he could readily turn the tip of the tongue to the left, but not to the right. Protrusion of the tongue requires the action of extrinsic tongue muscles, but lateral movements of the nonprotruded tongue are accomplished by intrinsic tongue muscles.