Bilateral sternocleidomastoid and trapezius palsy, which occurs with primary disease of muscles—for example, polymyositis and muscular dystrophy—may be difficult to distinguish from a bilateral damage to the accessory nerves or the motor nuclei (progressive bulbar palsy).
The Twelfth, or Hypoglossal, Nerve
This is also a pure motor nerve, which supplies the somatic musculature of the tongue. It arises as a series of rootlets that issue from the ventral medulla between the pyramid and inferior olivary complex. The nerve leaves the skull through the hypoglossal foramen and innervates the genioglossus muscle, which acts to protrude the tongue; the styloglossus, which retracts and elevates its root; and the hypoglossus, which causes the upper surface to become convex. Complete interruption of the nerve results in paralysis of one side of the tongue. The tongue curves slightly to the healthy side as it lies in the mouth, but on protrusion it deviates to the affected side, owing to the unopposed contraction of the healthy genioglossus muscle. By pushing against the patient’s tongue in the cheek, one can judge the degree of weakness. Patients with lesions of the hypoglossal nerve will have difficulty moving the tongue with natural facility, causing difficulty with handling food in the mouth as well as lingual dysarthria. Over time, the denervated side becomes wrinkled and atrophied, and fasciculations become apparent.
Isolated lesions of the hypoglossal nerve roots are rare. Occasionally an intramedullary lesion, usually a stroke, damages the emerging fibers of the hypoglossal nerve, corticospinal tract, and medial lemniscus (see Table 33-3). The result is paralysis and atrophy of one side of the tongue, together with spastic paralysis and loss of vibration and position sense in the opposite arm and leg. Poliomyelitis and motor neuron disease may destroy the hypoglossal nuclei. The latter is the most common cause of a bilaterally atrophic and fasciculating tongue. Lesions of the basal meninges and of the occipital bones (tumor invasion, platybasia, invagination of the occipital condyles, Paget disease) may involve the nerve in its extramedullary course, and it is sometimes damaged in operations on the neck including carotid endarterectomy. Goodman and coworkers showed a dissecting aneurysm of the carotid artery to have compressed the hypoglossal nerve, with resultant weakness and atrophy of the tongue. Rare instances of temporal arteritis and Takayasu arteritis affecting the carotid artery and adjacent twelfth nerve have been described. Lance and Anthony have described the simultaneous occurrence of nuchal-occipital pain and ipsilateral numbness of the tongue, provoked by the sudden, sharp turning of the head and termed it the neck–tongue syndrome. The phenomenon has been attributed to compression in the atlantoaxial space of the second cervical root, which carries some of the sensory fibers from the tongue, via the hypoglossal nerve, to the C2 segment of the spinal cord.
It is worth mentioning here that the tongue is often red and smooth in vitamin-deficiency states. Glossodynia (burning mouth syndrome discussed in Chap. 9), a condition most frequently seen in the elderly and in young women, may or may not be accompanied by redness and dryness, but not by lingual weakness. A habit of tongue-thrusting and teeth-clenching is often associated. The ascription of these motor abnormalities to a psychogenic mechanism does not agree with the authors’ experience (see Quinn).