Continuing Education Activity

Trigeminal neuropathy (TNO) refers to the dysfunction of sensory or motor functions involving cranial nerve V (trigeminal nerve). Trigeminal neuropathy commonly manifests with sensory symptoms such as numbness in the region innervated by the trigeminal nerve, sometimes associated with other paresthesias or pain. Motor symptoms are less common and can present as masticatory weakness. The etiology of trigeminal neuropathy is broad and poses a diagnostic challenge to physicians. Trigeminal neuropathy can sometimes be the first manifestation of a tumor or autoimmune disease. This article aims to educate about the identification and management of trigeminal neuropathy. This activity stresses the role and importance of multidisciplinary team collaboration to provide well-coordinated care for enhanced patient outcomes.

Objectives:

• Identify the clinical signs and symptoms of trigeminal neuropathy (TNO) in patients, including numbness, sensory disturbances, and motor weakness.

• Differentiate between trigeminal neuropathy (TNO) and trigeminal neuralgia based on the nature of pain (continuous vs. paroxysmal), associated sensory or motor deficits, and relevant medical history.

• Implement knowledge of trigeminal nerve anatomy by using evidence-based diagnostic protocols, including neuroimaging and laboratory tests, to identify the location and etiology of trigeminal neuropathy and establish a comprehensive care plan.

• Collaborate with multidisciplinary healthcare teams, including neurologists, radiologists, and pain specialists, to provide comprehensive care for patients with trigeminal neuropathy, addressing both the neurological and psychological aspects.

Introduction

Trigeminal neuropathy refers to dysfunction in sensory or motor functions involving cranial nerve V, the trigeminal nerve.[1] Trigeminal neuropathy (TNO) typically presents with numbness in the region innervated by the trigeminal nerve, sometimes associated with paresthesias, pain, or masticatory weakness. TNO can present from the involvement of the fifth cranial nerve (CN V) anywhere in its course, from the nuclei in the brain stem to its peripheral branches. It can be caused by known etiologies such as traumas, tumors, rheumatologic diseases, demyelinating, or idiopathic ones. Sometimes, TNO can be the initial manifestation of an underlying tumor or a relapse from a known neoplastic process.[2] Multiple sclerosis, glioma, and infarct are the most commonly reported abnormalities in the brain stem that cause trigeminal neuropathy. Neurovascular compression, schwannomas, and meningiomas are common cisternal causes.[3][4] Unilateral TNO could be secondary to focal lesions, while bilateral, symmetric presentations can be seen with connective tissue diseases or idiopathic etiology.[5] TNO can cause facial pain in the distribution of one or more trigeminal nerve branches. The pain in trigeminal neuropathy is usually continuous, described as burning or squeezing, and is often accompanied by allodynia and cold hyperalgesia. While the symptoms of TNO can be concerning, it is most important to rule out potentially harmful underlying conditions such as malignancy, vascular malformation, and autoimmune diseases. 

Trigeminal neuralgia should not be confused with trigeminal neuropathy.[6][7] Trigeminal neuralgia is a paroxysmal, electric shock-like pain that is abrupt in onset and termination, without sensory loss or motor weakness. Classic trigeminal neuralgia can be due to neurovascular compression of CN V. Secondary trigeminal neuralgia is caused by various conditions like multiple sclerosis, vascular malformation, or autoimmune disease.[6]

Anatomy of CN V

The trigeminal nerve is the largest cranial nerve and has both sensory and motor components with complex anatomy. The nerve course can be divided into four segments: brainstem, cisternal, Meckel's cave/cavernous sinus, and extracranial.[4]

1) Sensory and motor nuclei

The brainstem contains the 1 motor and 3 sensory nuclei of the trigeminal nerve. The sensory nuclei include the mesencephalic nucleus, principal sensory nucleus, and spinal nucleus.[8][9] Their functions are as follows: 

• Mesencephalic nucleus—in the midbrain. It receives and transmits proprioception from the orofacial region and is responsible for unconscious proprioception from muscles of mastication and other head and neck muscles. It also serves as an afferent limb of the jaw jerk reflex.
• Principle sensory nucleus—in the upper pons. It is responsible for conscious proprioception, fine touch, vibration, and two-point discrimination.[8]
• Spinal nucleus—lower pons to cervical cord up to the C2-C4 level. It is composed of the oralis, interpolaris, and caudalis subnuclei. It is responsible for crude touch, pain, and temperature sensations. It also receives afferent fibers from cranial nerves VII, IX, and X.[8]
• Motor nucleus —upper pons on the lateral surface of the pontine tegmentum. It supplies the small motor root, which joins V3 (the mandibular division of the trigeminal nerve), bypassing the trigeminal ganglion.

2) Nerve entry and intracranial anatomy

• The nerve root entry zone is the cisternal segment where the cranial nerve V enters the prepontine cistern. This area can be affected by vascular compression, infections, and neoplasms.
• The nerve then travels through the prepontine cistern to Meckel's cave by an opening called Porus trigeminal or dural foramen.
• Within the Meckel's cave (also called the trigeminal cave or Meckel cavern) lies the ganglion of the sensory branch, which is called the trigeminal, semilunar, or Gasserion ganglion. This ganglion consists of the nerve bodies of pseudounipolar neurons, which have one axon directed to the periphery (skin, tissue, or muscles) and one axon directed to the nuclei in the brainstem.
• The trigeminal nerve then divides into three subdivisions: ophthalmic (V1), maxillary (V2), and mandibular (V3) nerves.
• The ophthalmic (V1) and the maxillary (V2) divisions cross the cavernous sinus on its lateral wall, inferior to the abducens nerve. The ophthalmic nerve (V1) exits the skull via a superior orbital fissure. The maxillary (V2) nerve exits the skull via foramen rotundum. The mandibular (V3) nerve exits the skull via foramen ovale.
• The motor root passes under the ganglion in Meckel's cave. Fibers of the motor root are distributed to the V3 division of the trigeminal nerve.

3) Trigeminal nerve divisions after the trigeminal ganglion

• Ophthalmic (V1) is the smallest division and is a pure sensory nerve. It has 3 terminal branches (frontal, lacrimal, nasociliary). It supplies the eye (upper eyelid, conjunctiva, cornea), scalp, forehead, frontal sinus, ethmoid sinus, and dorsum of the nose. It also provides a parasympathetic supply to the lacrimal gland.
• The maxillary nerve (V2) has 14 terminal branches, supplying the lower eyelid and its conjunctiva, cheeks, maxillary sinus, superior palate, upper lip, upper molar, incisor, canine teeth (and the associated gingiva). It also provides a parasympathetic supply to the lacrimal gland and mucous glands.
• The mandibular nerve (V3) is the largest division and has 4 terminal branches: auriculotemporal nerve, buccal nerve, inferior alveolar nerve, and lingual nerve. It provides the only motor functions of CN V. 

4) Trigeminal nerve function

• Sensory supply includes most of the face from mid-cranium to the lower chin, including the eye and external ear, and the general sensation of anterior 2/3rds of the tongue. 
• Motor branches innervate four muscles of mastication (temporalis, master, medial pterygoid, lateral pterygoid). They also supply 4 other muscles—mylohyoid, anterior belly of digastric, tensor tympani, and tensor veli palatini muscles.
• CN V also innervates parts of the sympathetic nervous system via V1 and the parasympathetic system via V1, V2, and V3, including the submandibular, sublingual, and parotid glands. 

Etiology

The causes of trigeminal neuropathy range from benign to life-threatening causes. In addition to the causes of TNO listed below, cranial nerve V can also be a source of intracranial spread of infectious or neoplastic processes.

Etiology of Trigeminal Neuropathy Trauma: Accidental and iatrogenic injuries are the most common causes of TNO, causing up to 40% of cases. Dental procedures, particularly third molar extractions and the anesthesia related to dental procedures, commonly injure the inferior alveolar nerve and lingual nerve (branches of V3), resulting in sensory deficits in these areas.[10] Penetrating and blunt head trauma can also cause TNO, especially in the V2 region.[11]

Neoplastic: Neoplasm is an important cause of TNO that should be excluded. Mechanisms causing TNO include intracranial and extracranial nerve compression, perineural spread, and metastatic disease. A retrospective review found that numbness in the distribution of the mental branch of V3 (the anterior chin and lower lip area) is an especially poor prognostic indicator. This "numb chin" sign was the primary symptom of malignant disease in 28% of cases and the first symptom of recurrent disease in 38% of cases.[12] 

Common tumor locations resulting in TNO include the brainstem, prepontine cistern, cerebellar-pontine angle, trigeminal ganglion, and cavernous sinus. A rare but serious complication of malignancy is cavernous sinus syndrome. The cavernous sinus contains the third, fourth, and sixth cranial nerves, V1, V2, the carotid artery, and the sympathetic plexus. Cavernous sinus syndrome can present as ophthalmoplegia, ptosis, and TNO due to primary tumors, extension from local tumors (such as a pituitary malignancy), or metastatic disease.[13]

Perineural spread (neoplastic invasion along nerve pathways) is underrecognized as a conduit for malignancy transmission. This mode of transmission is especially common with head and neck cancers, and one of the first signs of perineural spread is pain and paresthesia, which can manifest as TNO.[14][15]

Some common malignancies causing metastatic disease presenting as TNO include lung cancer, breast cancer, head and neck cancers, and non-Hodgkin's lymphoma. Another metastatic cause of TNO is a leptomeningeal disease (also called leptomeningeal carcinomatosis or neoplastic meningitis), where tumor cells infiltrate the brain, spinal cord, and cerebrospinal fluid.[11][14][16]

Vascular: Vascular malformation, hemorrhage, or ischemia can cause a TNO presentation, and symptoms will depend on the location of the insult. Examples are: a lateral medullary infarction can cause ipsilateral loss of facial pain/temperature (but not touch/proprioception), dysarthria and contralateral hemiparesis; or a cavernous hemangioma in Meckel's cave can cause compression of V1, V2, and rarely V3.[17][18]

Autoimmune/inflammatory: The most common diseases in this category causing TNO are mixed connective tissue disorder, scleroderma, progressive systemic sclerosis, and Sjögren's syndrome. They are almost always purely sensory and may involve neuropathic pain. Manifestations can occur in all three divisions of CN V and can be unilateral or bilateral. Symptomatic patients with mixed connective tissue disorder often have high titers of anti-nuclear ribonucleoprotein RNA (anti-RNPn) antibodies.[2] Sjögren's syndrome often presents initially as isolated sensory neuropathy and is also associated with autonomic signs such as orthostatic hypotension and pupillary abnormalities.[19] Multiple sclerosis can also cause TNO, although it usually does not present as isolated cranial neuropathy. Neurosarcoidosis can also present as TNO and, radiographically, may mimic a mass lesion.[20]

Infections: Infectious causes are not often linked with cranial neuropathy but are still an important etiology to consider. In the developing world, leprosy is a significant cause of trigeminal and facial neuropathy, especially in the V2 distribution.[21]

Herpes simplex viruses are often implicated in Bell Palsy, a peripheral CN VII palsy; however, up to 25% of cases also display ipsilateral facial numbness, suggesting trigeminal sensory neuropathy.[22] The varicella-zoster virus is also thought to reside in the trigeminal nerve and can present as a painful, vesicular rash of shingles and rarely can present without a rash. It most commonly presents in the V1 distribution.[11][23] Neurosyphilis and Lyme disease (caused by the spirochete Borrelia burgdorferi)  have also been shown to cause TNO.[24][25]

Other: There are many case reports of other conditions which can rarely cause TNO. Some of these conditions include congenital malformations—such as skull base abnormalities, Arnold Chiari malformations, Moebius syndrome, and congenital trigeminal anesthesia; sickle cell anemia crises; amyloidosis; and toxic poisoning by trichloroethylene or stilbamidine.[2][11][26][27]

Idiopathic trigeminal sensory neuropathy: After extensive evaluation, if no cause can be found, TNO is labeled idiopathic. Although symptoms can last several years, about half of patients diagnosed with an idiopathic cause will recover without treatment. It is important to note that follow-up neurologic exams and imaging are required, as TNO can be the initial manifestation of underlying neoplastic or autoimmune diseases.[2]

Raeder paratrigeminal syndrome: This is an uncommon yet important syndrome to recognize and diagnose. The syndrome consists of a unilateral Horners syndrome with ptosis and miosis without facial sweating impairment, associated with unilateral headache or facial pain, with or without trigeminal sensory impairment. The third-order oculopupillary sympathetic fibers join the internal carotid artery to form a plexus. They travel with the trigeminal and oculomotor nerves in the cavernous sinus and the middle cranial fossa. Any lesion along the course of the internal carotid artery, especially in the middle cranial fossa, may produce the Raeder syndrome. Various causes may produce this syndrome, including internal carotid aneurysm or dissection, trauma, tumor, granulomatous inflammatory disorders, and cluster headache. It is important to image the internal carotid or middle cranial fossa to identify the cause.[28][29]

Epidemiology

The prevalence of trigeminal neuropathy can be challenging to identify. One study examining one etiology of TNO surveyed 535 oral and maxillofacial surgeons in California; it found that injuries caused to the inferior alveolar nerve and lingual nerve were 94.5% and 53%, respectively, as reported by the surgeons during their professional lifetimes.[2]

Pathophysiology

The pathophysiology of TNO is varied and depends on etiology. For example, iatrogenic trauma during dental procedures most commonly causes damage to the inferior alveolar nerve and the lingual nerve due to proximity to the molars. This manifests as an altered sensation in the lower lip, chin, lower teeth, gingiva, and tongue.[2][30] The inferior alveolar nerve can also be damaged by trauma from a dental implant and is also concerning for metastatic neoplastic disease in the absence of traumatic injury.[30][31]

When caused by a neoplastic process, TNO can sometimes be the initial complaint. Trigeminal nerve involvement can be due to the direct spread of tumors located in the nasopharynx, maxillary sinus, mandibular region, pontocerebellar angle, trigeminal ganglion, or tumors affecting other cranial nerves.[32][33][34][35]

TNO related to systemic inflammatory diseases such as Sjögren's syndrome, scleroderma, or other connective tissue disorders is associated with immunoglobulin deposits along the nerve, immunoglobulins and proteins in the cerebrospinal fluid, vasculitis, and other autoimmune processes. Connective tissue disorders should be strongly considered in differential if TNO has purely sensory involvement.[36][37][38]

In infectious cases like leprosy and syphilis and some inflammatory diseases like sarcoidosis, chronic granulomas directly impinge on the trigeminal nerve.[39][40]

History and Physical

Patients with TNO usually complain of one of the following cutaneous symptoms:

1. Hypoesthesia—partial loss of sensation in the distribution of the affected nerve.
2. Anesthesia—complete loss of sensation in the distribution of an affected nerve.
3. Hyperesthesia—aberrant discomfort (such as burning, itching, or rarely pain), which is perceived along with decreased or loss of sensation in the distribution of the affected nerve.[2]

Visual symptoms are often very prominent when V1 is involved due to its sensory innervation of the cornea, iris, ciliary body, and lacrimal gland. Corneal abrasions and vision loss are common visual symptoms. The corneal reflex should be tested, which involves CN V and VII.[11]

Motor manifestations may include masticator muscle spasms, weakness, or trismus. An abnormal (usually hyperreflexic) jaw reflex may also be present.[3]

A careful clinical exam should be done to evaluate other possible cranial nerve deficits, especially looking for deficits in cranial nerves VI, VII, and VIII. The involvement of multiple nerves could suggest a tumor in the pontocerebellar angle.[41] .

Painful TNO: Trigeminal neuropathic pain is different from trigeminal neuralgia. It is a continuous pain in the distribution of one or more divisions of the trigeminal nerve and can be associated with sensory changes within the trigeminal nerve distribution, allodynia, and cold hyperalgesia.[6] Trigeminal neuralgia, on the other hand, is a paroxysmal electric shock-like pain, abrupt in onset and termination, and without sensory loss or motor weakness.

There are three major groups of trigeminal neuropathic pain:[7]

1. Trigeminal neuropathic pain from herpes zoster infection
2. Trigeminal post-herpetic neuralgia (PHN)
3. Post-traumatic trigeminal neuropathic pain

Motor symptoms can include reduced strength in the muscles of mastication. The temporalis muscle should be examined for tone and the masseter muscle for strength. Weakness of the masseter muscle can result in difficulties with eating, drinking, and speaking.[11]

Evaluation

Often, clinical findings are inaccurate in localizing the lesion affecting the trigeminal nerve in its pathway. Further studies are needed to determine the etiology, including blood work, cerebrospinal fluid (CSF) evaluation, and radiological evaluation of the entire trigeminal nerve pathway. Blood work and CSF studies evaluate infectious causes, such as herpes, syphilis, or leprosy, and inflammatory etiologies, like multiple sclerosis, connective tissue disorders, Sjögren's syndrome, and sarcoidosis.[42] Studies for autoimmune or rheumatologic disorders are especially useful when other suggestive systemic signs are present. Some of these studies include serum immunoglobulin levels, complement levels, antinuclear antibody, anti-Ro (SS-A), anti-La (SS-B), anti-double-stranded DNA, and anti-RNPn antibodies. A salivary biopsy is sometimes performed if clinical suspicion for Sjögren's syndrome is high.

Complete radiological assessment is necessary to evaluate for possible paranasal sinuses, skull base, trigeminal ganglion, pontocerebellar angle, brainstem, or cortex lesions.[43] Radiological examinations include plain radiographs of the orofacial area, CT scan of the paranasal sinuses, maxillofacial area, and brain, and  MRI of the brain with and without gadolinium. High-resolution CT scan is thought to be 90% effective in diagnosing cerebellopontine angle tumors.[44] MRI with gadolinium is considered the best mode for evaluating the course of the trigeminal nerve, especially for the pontocerebellar angle, internal auditory canal area, and brainstem.[41][45] It is prudent to obtain T2-weighted images for the brain and T1-weighted axial and coronal high-resolution images (3mm thick sections) of the skull base with and without contrast for better evaluation. The MRI should be extended to the inferior mandibular area if the mandibular nerve is involved on the clinical exam. Fat-suppressed images can be obtained to evaluate for perineural tumor spread. MR angiogram and CT angiogram can also be obtained to evaluate for aneurysms or vascular malformations that could be compressing the trigeminal nerve. MR venogram and CT venogram should be considered for evaluation of the trigeminal nerve traversing through the cavernous sinus.[3]

Treatment / Management

The management of TNO varies based on the underlying cause of the symptoms. Pain can sometimes be the most pronounced symptom initially. A goal is at least a 30% reduction in pain for clinical significance.[46] Overall, treating neuropathic pain is challenging, necessitating a comprehensive, multi-pronged approach.

Neuropathic pain: The first treatment of choice includes tricyclic anti-depressants (TCAs), serotonin-norepinephrine reuptake inhibitors (SNRI), or gabapentinoids (gabapentin, pregabalin). [47] TCAs and SNRIs act primarily by blocking the reuptake of serotonin and noradrenaline. TCAs also affect various other channels, including sodium channels, which can lead to cardiotoxicity in overdose cases. TCAs also exhibit antihistamine and anticholinergic effects, which can result in drowsiness, dry mouth, or dizziness.[47] Gabapentinoids act by binding to and inhibiting the α2δ-1 subunit of voltage-gated calcium channels. While common side effects such as dizziness and drowsiness may occur, severe side effects are rare.

Second-line options include adjunctive use of topical lidocaine or capsaicin. Topical medications are easy to use and have fewer systemic side effects and interactions, but their effectiveness may limited if used intraorally due to saliva.[48] Opioids are usually a third-line choice. Even though there is some evidence supporting opioid efficacy in specific neuropathies like post-herpetic neuralgia, opioids are not the preferred choice due to associated risks of abuse and mortality.[48]

The selection of medications should be customized based on the patient’s individual profile, coexisting medical conditions, and the patient’s preferences. It is common to employ a combination of medications from various drug classes. Among TCAs, nortriptyline is the preferred choice as it has lower sedative properties and fewer anticholinergic side effects compared to amitriptyline. Among SNRIs, duloxetine has the highest level of evidence-based data for treating neuropathic pain. Limited data from small trials suggests that carbamazepine may be effective in managing other forms of chronic neuropathic pain.[49] The use of intravenous ketamine and lidocaine infusions for chronic pain has yielded mixed results.[50][51] Medications that are not recommended include muscle relaxants and benzodiazepines.[52][53]

Refractory pain: Botulinum toxin injections, neuroablation, cryotherapy, and neuromodulation are reserved for patients who do not respond to conventional treatments and have persistent or refractory symptoms.[54] Neuromodulation techniques have also been used, including transcutaneous nerve stimulation, pulsed radiofrequency, and spinal cord stimulation. These techniques have variable results.[11][55] 

Treatment of underlying cause: Addressing the root cause can be effective in reducing the duration and intensity of symptoms. For instance, steroid therapy can be employed to manage neuropathic pain associated with sarcoidosis; surgical excision may be considered for tumors affecting the trigeminal nerve; and antimicrobial medications are indicated with infectious causes. Acyclovir has been used with benefit in some patients with idiopathic TNO, suggesting an element of herpes virus reactivation. Steroids have also been prescribed for idiopathic TNO with variable results.[56][57]

Psychosocial factors: Patients experiencing chronic pain face an increased likelihood of developing depression, which in turn can exacerbate the underlying pain symptoms. Consequently, addressing concurrent depression is essential for effectively managing neuropathic pain. Cognitive behavioral therapy (CBT) may prove beneficial for certain patients struggling with persistent pain, aiding in enhancing their quality of life.[58]

Differential Diagnosis

The differential for TNO includes conditions that present with similar sensory or motor deficits or with pain in the trigeminal nerve distribution and includes the following: 

Trigeminal neuralgia: severe paroxysmal pain lasting from seconds to 2 minutes in the distribution of trigeminal nerve. This is an important distinction to make and most likely to confound the diagnosis of TNO.

Persistent idiopathic facial pain: daily recurring facial and/or oral pain without neurologic deficits, lasting over 2 hours a day for over 3 months.[59]

Central neuropathic pain: related to underlying central causes such as multiple sclerosis or post-stroke pain rather than CN V. 

Primary stabbing headache: transient, sharp jabbing pains that occur at variable locations within trigeminal and cervical dermatomes lasting for a few seconds. There are often multiple episodes in a day.[60]

First bite syndrome: paroxysmal facial pain induced by the first bite of a meal with subsequent lessening on further bites.[61]

Paroxysmal hemicrania: pain is most often in the ophthalmic trigeminal distribution, lasting minutes to less than 2 hours, and is associated with ipsilateral autonomic features such as lacrimation, redness of eyes, nasal stuffiness, ptosis, facial swelling, and flushing.[62] The neurological exam is non-focal. 

Short-lasting unilateral neuralgiform headache attacks: often associated with conjunctival injection and tearing (SUNCT) or cranial autonomic symptoms (SUNA). This is characterized by sudden, multiple bursts of severe pain in any of the three divisions of the trigeminal nerve lasting a few seconds to minutes.[62] The neurological exam is non-focal.  

Dental pain: dull, throbbing, continuous pain triggered by intra-oral manipulation such as brushing or chewing food.  

Prognosis

Overall prognosis depends on the underlying etiology of TNO. A tumor compressing the trigeminal nerve, such as a meningioma, may be removed and cured with surgery. A granulomatous lesion may respond to immunomodulating agents.

Managing neuropathic pain poses significant challenges. Recovery is uncommon if there is an underlying connective tissue disorder and is poor if it is related to malignancy.

Some patients with neuropathic pain may not respond well to drugs. Botulinum toxin injections, nerve ablation, and neuromodulation are typically reserved for patients who have not responded well to conventional treatments and have persistent or refractory symptoms, but results are often equivocal.

Complications

There are various reported complications of trigeminal neuropathy:

Neurotrophic keratitis can be a complication of TNO. Patients are at risk of developing corneal ulceration. Treatment is aimed at corneal protection and preventing vision loss.[63]

Trigeminal trophic syndrome is characterized by skin ulceration and dysesthesias related to damage in the trigeminal system. The most frequent causes are therapeutic trigeminal nerve ablation and ischemic medullary or pontine stroke; other causes include craniofacial surgery, trauma, and herpes zoster infection. Treatment is aimed at symptomatic management, promotion of skin healing, and prevention of skin infections.[64]

Numb chin syndrome is reduced or absent sensation in an area over the chin and lower lip in the distribution of the inferior alveolar or mental nerve. The most common causes are iatrogenic, particularly removal of the molars. Other possibilities include metastasis, drugs such as mefloquine, allopurinol, infections (Lyme disease, HSV, and syphilis), multiple sclerosis, giant cell arteritis, connective tissue disorders, sarcoidosis, and thalamic stroke. Numbness in this distribution can be a harbinger of more serious conditions.[12]

Deterrence and Patient Education

Patients require education on the signs and symptoms of trigeminal neuropathy. Patients should be made aware that underlying conditions are possible; therefore, thorough investigation and close follow-up are recommended. Primary care providers can diagnose TNO, but a referral to general neurology is warranted to help identify possible etiologies. Follow-up with neurology is recommended even if the initial neurologic exam does not show deficits to rule out underlying pathology such as autoimmune or neoplastic disease. Consultation with a neurosurgeon or neurovascular surgeon is required for patients with identifiable surgical etiologies to assess the necessity of surgical procedures.

Pearls and Other Issues

Trigeminal neuropathy typically presents with numbness in the region innervated by the trigeminal nerve, sometimes in association with other paresthesia, pain, or masticatory weakness.

It is important to differentiate trigeminal neuropathy from trigeminal neuralgia, which presents as brief and episodic pain without associated sensory or motor symptoms. Trigeminal neuralgia is usually perceived as an electric shock-like pain.

Unilateral trigeminal TNO could be secondary to focal lesions.

Bilateral, symmetric TNO can be seen with autoimmune and inflammatory diseases and with idiopathic etiology.

Chin numbness is often associated with neoplastic disease; without preceding trauma, it is a poor prognostic indicator.

Cavernous sinus syndrome can present as ophthalmoplegia, ptosis, and TNO in the V1/V2 distribution due to primary tumors, extension from local tumors (such as a pituitary malignancy), or metastatic disease. Lesions in this area can also cause ipsilateral Horner syndrome.

A lateral medullary infarction can cause ipsilateral loss of facial pain/temperature (but not touch/proprioception), dysarthria, and contralateral hemiparesis.

A cavernous hemangioma in Meckel's cave can cause compression of V1, V2, and rarely V3.

Sjögren's syndrome often presents initially as isolated sensory neuropathy and is also associated with autonomic signs such as orthostatic hypotension and pupillary abnormalities, as well as the classic signs of dry eyes, dry mouth, and joint pain.

Clinical findings are often inaccurate in localizing the lesion affecting the trigeminal nerve. Therefore, further studies are needed to determine the etiology, including blood work, CSF evaluation, and radiological evaluation of the entire trigeminal nerve pathway.

The first treatment of choice for TNO pain includes tricyclic anti-depressants (TCAs), serotonin-norepinephrine reuptake inhibitors (SNRI), or gabapentinoids (gabapentin, pregabalin).

Even if the initial work-up does not reveal a causative agent, neurologic follow-up is required because TNO can be an initial symptom of underlying neoplastic or autoimmune disease.

Enhancing Healthcare Team Outcomes

An extensive interprofessional team approach consisting of primary care physicians, emergency physicians, neurologists, neurosurgeons, dentists, and pharmacists is required to facilitate timely, accurate evaluation and treatment of trigeminal neuropathy. When a primary care physician or emergency room physician evaluates a patient with abnormal facial sensations and is concerned about TNO, a referral to a neurologist is highly recommended. All team members should collaborate and engage in open communication to optimize patient care and outcomes. When TNO is suspected, neuroimaging is warranted to evaluate possible etiologies. Pharmacists should offer education about prescribed medications and their adverse effects.