How do you clinically assess the hypoglossal (twelfth cranial) nerve in a normal individual?

Clinical Examination of the Hypoglossal Nerve (CN XII)

Ask the patient to protrude their tongue and observe for deviation toward the side of any lesion, which is the primary clinical sign of hypoglossal nerve palsy. 1

Examination Technique

Inspection at Rest

• Observe the tongue at rest inside the mouth for atrophy, fasciculations, or asymmetry of the tongue musculature, which indicate chronic denervation. 1, 2
• Look for unilateral wasting or fatty infiltration, which may be visible as decreased bulk on the affected side. 1

Tongue Protrusion Test

• Instruct the patient to stick out their tongue and observe the direction of deviation. 1, 3
• In hypoglossal nerve palsy, the tongue deviates toward the side of the lesion upon protrusion due to unopposed action of the contralateral genioglossus muscle. 1, 3
• The genioglossus muscle normally protrudes the tongue forward and to the opposite side; when paralyzed, the intact contralateral muscle pushes the tongue toward the weak side. 2

Assessment of Tongue Movements

• Ask the patient to move the tongue side to side to assess lateral movement strength and coordination. 4
• Test tongue strength by having the patient push the tongue against the inside of each cheek while you apply resistance from outside. 4
• Evaluate for weakness or reduced range of motion on the affected side. 2

Speech Assessment

• Listen for dysarthria, particularly difficulty with lingual consonants (t, d, l, n), which indicates impaired tongue motor function. 1, 3
• Dysarthria is a key clinical manifestation of hypoglossal nerve dysfunction. 1

Normal Findings in a Healthy Individual

• The tongue protrudes in the midline without deviation to either side. 1
• Symmetric tongue bulk and contour bilaterally without atrophy or fasciculations. 2
• Full strength with lateral tongue movements and resistance testing. 4
• Normal articulation without dysarthria. 3

Anatomical Basis

• The hypoglossal nerve provides somatic motor innervation to all intrinsic tongue muscles (superior longitudinal, inferior longitudinal, transverse, and vertical muscles) and three extrinsic tongue muscles (styloglossus, hyoglossus, and genioglossus), with the exception of the palatoglossus muscle. 1, 3, 2
• The nerve exits the skull through the hypoglossal canal and travels caudally within the carotid space before coursing anteriorly inferior to the hyoid bone. 3, 5

Common Pitfalls

• Do not confuse tongue deviation with facial asymmetry from facial nerve (CN VII) palsy, which affects facial muscles but not tongue protrusion. 1
• Fasciculations may be subtle and require careful observation with the tongue at rest inside the mouth for 30-60 seconds. 2, 6
• Bilateral hypoglossal nerve palsy may not show deviation but will demonstrate reduced tongue protrusion and strength bilaterally. 4