## **Core Concept**
The hypoglossal nerve (cranial nerve XII) is responsible for controlling the intrinsic and extrinsic muscles of the tongue, except for palatoglossus. Unilateral injury to the hypoglossal nerve affects the motor function of the tongue on the same side as the injury.

## **Why the Correct Answer is Right**
In the case of unilateral hypoglossal nerve injury, the clinical manifestations include weakness or paralysis of the ipsilateral tongue muscles, leading to difficulty in protruding the tongue, deviation of the tongue towards the side of the lesion upon protrusion, and possible changes in speech and swallowing. However, the question asks for an exception among the provided options.

## **Why Each Wrong Option is Incorrect**
- **Option A:** Difficulty in protruding the tongue is a manifestation of hypoglossal nerve injury because the nerve controls the genioglossus muscle, which is essential for tongue protrusion.
- **Option B:** Deviation of the tongue towards the side of the lesion upon protrusion occurs due to the weakness of the genioglossus muscle on the affected side, making this a correct manifestation.
- **Option C:** Changes in speech (dysarthria) can occur due to impaired tongue movements necessary for articulation.
- **Option D:** Since the question does not specify what the options A, B, C, or D are, we must infer based on common manifestations. Typically, unilateral hypoglossal nerve injury does not cause **dysphagia (swallowing difficulties)** that is severe or directly attributable to the injury alone, as the primary nerves involved in swallowing include the vagus nerve (cranial nerve X), and the spinal accessory nerve (cranial nerve XI) for some muscles. However, without specific options provided, we focus on the typical effects.

## **Clinical Pearl / High-Yield Fact**
A key clinical test for assessing hypoglossal nerve function is asking the patient to protrude their tongue. Normally, the tongue protrudes straight out. With a unilateral hypoglossal nerve injury, the tongue deviates towards the side of the lesion due to the unopposed action of the intact genioglossus muscle on the contralateral side.

## **Correct Answer:** D.