The ophthalmic division of the fifth nerve may be involved in the wall of the cavernous sinus in combination with the third, fourth, and sixth nerves by a variety of processes, including thrombosis of the cavernous sinus. Tumors of the sphenoid bone (myeloma, metastatic carcinoma, squamous cell carcinoma, and lymphoepithelioma of the nasopharynx) may involve branches of the trigeminal nerve at their foramina of entry or exit. An unusual perineural infiltration of superficial branches of the nerve by squamous cell skin cancers of the face is discussed further on under “Multiple Cranial Nerve Palsies.” The mandibular division of the nerve may be compressed by the roots of an impacted third molar (wisdom) tooth. Well known to clinicians is a sign of numbness of the chin and lower lip from infiltration of the mental nerve as the first indication of metastatic carcinoma of the breast, prostate, or multiple myeloma. Massey and colleagues have described the details of 19 such cases of the “numb chin” sign.
Neurologists also encounter instances of slowly evolving unilateral or bilateral trigeminal neuropathy in which sensory impairment is confined to the territory of the trigeminal nerve, sometimes associated with pain, paresthesias, or disturbances of taste. This type of loss of facial sensation can also occur as part of a widespread sensory neuropathy or ganglionopathy that occurs as a paraneoplastic effect of cancer (see Chap. 30) or with Sjögren disease.
As common is an association between isolated trigeminal neuropathy and immune-mediated connective tissue diseases. Of 22 such cases described by Lecky and colleagues, 9 had either scleroderma or mixed connective tissue disease, and a similar number had either organor nonorgan-specific serum autoantibodies. Several specific antibody tests are used to establish the diagnosis of scleroderma. The symptoms may involve the other side of the face years later. Hughes has also described cases of trigeminal neuropathy with scleroderma, lupus erythematosus, and Sjögren disease. We have seen several patients with Sjögren disease in whom the trigeminal neuropathy and the associated antibodies or inflammation of the minor salivary glands were evident well before the characteristic sicca syndrome or other systemic manifestations of the disease. The condition may remain troublesome for years. Pathologic data are limited but point to an inflammatory lesion of the trigeminal ganglion or sensory root. Spillane and Wells, many decades ago, discussed an isolated trigeminal neuropathy (it had been called Spillane’s trigeminal neuritis). Four of their 16 patients had an associated paranasal sinusitis, but subsequent reports have failed to substantiate a causal relationship between sinusitis and cranial neuritis. One wonders how many of these individuals had connective tissue disease. A less common form of idiopathic trigeminal sensory neuropathy with which we have limited experience has an acute onset and a tendency to resolve completely or partially, in much the same manner as Bell’s palsy, with which it is sometimes associated (Blau et al). A recurrent variety of acute trigeminal symptoms of uncertain origin has been reported in the dental literature. Though rare because of limited use, toxicity from stilbamidine and trichloroethylene is known to cause sensory loss, tingling, burning, and itching exclusively in the trigeminal sensory territory. We have had experience with 2 patients whose facial numbness was a component of an upper cervical disc syndrome that included numbness on the same side of the body; presumably the cervical spinal trigeminal nucleus or tract was compressed. Facial numbness, of course, also occurs with diverse conditions such as syringomyelia that affect the spinal nucleus of the trigeminal nerve but there are additional signs of brainstem or upper cervical cord disease.