Does numbness matter? A clinical review of trigeminal neuropathy
This summary is based on the article published in Cephalagia: Numbness matters: A clinical review of trigeminal neuropathy (July 2011)
Jonathan H Smith and F Michael Cutrer
Trigeminal neuropathies are a group of clinical disorders that involve injury to primary first-order neurons within the trigeminal nerve.
Pain, while often the earliest and quite often the most pressing symptom, is only one feature of trigeminal disease, which may also include loss of sensation and/or masticatory weakness. Trigeminal neuropathy (TNO) is characterized by numbness in the skin or mucosal membranes in the distribution of the trigeminal nerves, and/ or neuropathic weakness in the muscles of mastication.
In TNO, pain may dominate the clinical picture early on, but as the disorder underlying it progresses and neurons are destroyed, numbness and weakness usually appear.
A spectrum of pathophysiological processes may affect the trigeminal nerves, including traumatic, vascular, inflammatory, demyelinating, infectious, and neoplastic disorders. Thus, the finding of facial numbness increases the likelihood that a worrisome condition may be present and necessitates a comprehensive evaluation. (1)
Pain is very likely to be a feature when sensory loss is associated with nasopharyngeal carcinoma or metastasis (2), although pain may be seen among the entire spectrum of pathogenic mechanisms.
Purpose of the Review
Health care professionals who evaluate patients with craniofacial pain should be aware of the appropriate evaluation, diagnosis, and management of secondary disorders involving the trigeminal pathways.
The aim of the article is tot review the spectrum of etiologies underlying both painful and non-painful trigeminal neuropathies, with attention to particularly dangerous processes that may elude the clinician in the absence of a meticulous evaluation. Complications and management issues specific to patients with trigeminal neuropathy are discussed.
In the routine evaluation of patients with facial pain, the clinician will inevitably be confronted with secondary pathology of the trigeminal nerves and nuclei. The appearance of numbness, even when pain continues to be the most pressing complaint, necessitates clinical assessment of the integrity of all aspects of the trigeminal pathways, which may also include neurophysiologic, radiographic, and laboratory evaluation.
Trauma is thought to be the most common mechanism leading to TNO, and may be either accidental or iatrogenic. (3, 4, 5) The inferior alveolar and lingual nerves are particularly susceptible to injury in the context of oral surgery, especially if the lower third molar is involved. (6, 5, 7)
Other rarer etiologies of traumatic TNO include denture trauma at the mental foramen (3), anterior superior alveolar injury from repetitive trumpet playing (8), following laser in situ keratomileusis (9), and sialolithiasis leading to lingual nerve compression. (10)
Trigeminal neuropathy may be the presenting manifestation of malignancy, by several distinct mechanisms, including compression at intra- or extra-cranial portions of the nerve, peri-neural spread, or metastasis.
Vascular hemorrhage or ischemia of the brainstem may underlie an acute onset of facial numbness. Pontine hemorrhages may mimic TNO in isolation or in combination with other neurological deficits, and are most commonly sequelae of hypertension, or more rarely vascular malformation. (11, 12)
Sensory trigeminal neuropathy is a well accepted complication of autoimmune connective tissue and inflammatory disease. (13, 14-19) Undifferentiated and mixed connective tissue diseases are most commonly associated with TNO, followed by scleroderma. (15)
Infection is not thought of as a common mechanism for TNO, although worldwide leprosy continues to be an important etiology of cranial neuropathy, particularly of the facial and trigeminal nerves. (20, 21)
Kennedy’s disease, or spinal-bulbar muscular atrophy, is an X-linked degenerative sensorimotor neuronopathy, associated with signs of androgen insensitivity. Either jaw-drop or isolated jaw-closure weakness may be a presenting feature. (22)
Sensory loss is considered minimal in this disorder, although neurophysiological assessment has disclosed abnormal trigeminal reflexes consistent with a ganglionopathy. (23)
Trichloroethylene toxicity has been reported in the context of both general anesthesia and industrial exposure (degreasing solvent) to result in TNO progressing over hours to days. Other cranial nerves may be involved, and recovery may be incomplete. (1, 24)
Congenital skull base anomalies and/or inherited bone disease may also manifest with either symptomatic trigeminal neuralgia or TNO. Chiari malformation, cranial osteodysplasia, achondroplasia, and osteogenesis imperfecta have been reported in this regard, in association with stretching of the nerve roots, and/or deformity of the posterior fossa. (25, 26)
In the evaluation of a patient with a pure trigeminal sensory syndrome, in which no underlying process can be identified, a diagnosis of idiopathic trigeminal sensory neuropathy can be ascribed. (1)
Complications and management of trigeminal neuropathy
Pain: Chronic trigeminal pain is perhaps the most immediately troubling symptom to many patients. In TNO, the pain may involve any of the three divisions and may be either unilateral or bilateral.
Numbness: Intraoral numbness is a particular troubling complication of TNO because of the inherent difficulties it causes in eating, management of saliva, and the problems associated with trauma to denervated tongue and buccal mucosa.
Neurotrophic keratitis: Neurotrophic keratitis (NK) is a degenerative corneal disease that may rarely develop in the setting of trigeminal
deafferentiation from the cornea. (27)
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