The characteristic features of trigeminal neuralgia are its paroxysmal facial pain, its unilaterality, the tendency to involve the second and third divisions of the trigeminal nerve, an intensity that makes the patient grimace or wince (tic), the presence of a trigger point on the face, the lack of demonstrable sensory or motor deficit, and its response in more than half of the cases to antiepileptic drugs (AEDs). The diagnosis of trigeminal neuralgia and its differentiation from other forms of intermittent facial pain described below—as well as from cluster headache, dental neuralgia, temporomandibular joint pain, and atypical facial pain—is usually not difficult, especially if there is a trigger point and no demonstrable evidence of sensory or motor impairment. Furthermore, the vascular compressive form is difficult to diagnose without high-resolution neuroimaging or exposure at operation and most such cases are therefore characterized as idiopathic until revealed as vascular in causation.
In rare instances, trigeminal neuralgia is preceded or accompanied by hemifacial spasm, a combination that Cushing called tic convulsif. This combination may be indicative of a tumor (cholesteatoma), an aneurysmal dilatation of the basilar artery or one of its branches, or an arteriovenous malformation that compresses both the trigeminal and facial nerves. Trigeminal neuralgia and glossopharyngeal neuralgia (pain in the tonsillar region) may also be combined in these conditions.
Trigeminal neuropathies and neuritis Of the conditions that damage the branches of the trigeminal nerve, facial and cranial injuries, and fractures are probably the most common, but they do not usually come to the attention of neurologists. The most superficial branches of the nerve—the supratrochlear, supraorbital, and infraorbital—are the ones usually involved by trauma. The sensory loss is present from the time of the injury, and partial regeneration may be attended by constant pain.
Of the various inflammatory and infectious diseases that affect the trigeminal nerves or ganglia, herpes zoster ranks first. Persistent pain after herpetic infection of the fifth nerve is a serious problem, that at times can be difficult to treat effectively. This subject is discussed in Chap. 9 with other forms of facial pain. Middle ear infections and osteomyelitis of the apex of the petrous bone may spread to the ganglion and root, also implicating the sixth cranial nerve (Gradenigo syndrome). HIV infection has not been clearly implicated in infection of the fifth nerve (as it has in the seventh nerve), but reactivation of latent herpes zoster is seen with AIDS.
The trigeminal root may be compressed or invaded by intracranial meningiomas, vestibular schwannomas, trigeminal schwannomas, cholesteatomas, and chordomas and by tortuous branches of the basilar artery. Sinus tumors and metastatic disease may also infiltrate the nerve, causing pain and a gradually progressive sensory loss. Demyelination at the trigeminal root entry point into the pons is another well-characterized cause in cases of multiple sclerosis (Fig. 44-2).