In a lower motor neuron CN XII palsy, the tongue deviates toward the side of the lesion. Which of the following best describes this deviation?

In a lower motor neuron CN XII palsy, the tongue deviates toward the side of the lesion. Which of the following best describes this deviation?

• A. Toward the lesion
• B. Away from the lesion
• C. No deviation
• D. Upward deviation

Answer: (A)

Unilateral weakness of the tongue muscles from a lower motor neuron lesion of the hypoglossal nerve makes the tongue deviate to the affected side when you try to protrude it. The genioglossus on the opposite, intact side still pushes the tongue outward, so the net result is a tongue that deviates toward the side of the lesion. This is a classic sign of CN XII LMN palsy and is often accompanied by atrophy and fasciculations on the involved side. By contrast, an upper motor neuron lesion would typically cause the tongue to deviate away from the lesion when protruded, and the other options don’t fit the pattern of focal, unilateral weakness seen with a CN XII LMN palsy.

Unilateral weakness of the tongue muscles from a lower motor neuron lesion of the hypoglossal nerve makes the tongue deviate to the affected side when you try to protrude it. The genioglossus on the opposite, intact side still pushes the tongue outward, so the net result is a tongue that deviates toward the side of the lesion. This is a classic sign of CN XII LMN palsy and is often accompanied by atrophy and fasciculations on the involved side. By contrast, an upper motor neuron lesion would typically cause the tongue to deviate away from the lesion when protruded, and the other options don’t fit the pattern of focal, unilateral weakness seen with a CN XII LMN palsy.