14.4 Trigeminal Neuralgia, Bell's Palsy and Giant Cell Arteritis

3. Neurological Conditions: Epilepsy, Stroke, and Cranial Neuropathies

Cranial Neuropathies: Trigeminal Neuralgia, Bell's Palsy, and Giant Cell Arteritis

                               Cranial Neuropathies
                                        │
      ┌─────────────────────────────────┼─────────────────────────────────┐
      ▼                                 ▼                                 ▼
Trigeminal Neuralgia (CN V)      Bell's Palsy (CN VII)       Giant Cell Arteritis (GCA)
• Unilateral, lancinating        • Acute idiopathic LMN      • Systemic vasculitis (>50 yrs)
  paroxysms (V2 / V3)              paralysis of whole face   • Temporal headache, scalp
• Triggered by light touch       • Forehead paralysed          tenderness
• Normal neuro exam              • Bell's phenomenon         • Pathognomonic Jaw Claudication
• Rx: Carbamazepine / MVD        • Rx: Prednisolone (72 hrs) • Visual loss emergency (AION)
                                 • Corneal eye protection    • Rx: High-dose Prednisolone

Trigeminal Neuralgia (Tic Douloureux)

• Clinical Presentation: Paroxysms of sudden, unilateral, lancinating, electric-shock-like, stabbing pain strictly localized along the anatomical distribution of one or more divisions of the trigeminal nerve. The maxillary (V2) and mandibular (V3) divisions are involved in $>95%$ of cases; the ophthalmic (V1) division is affected in $<5%$. Paroxysms last from a few seconds up to 2 minutes, followed by a refractory period during which further pain cannot be triggered.
• Trigger Zones: Pain is provoked by trivial non-noxious tactile stimuli applied to cutaneous or mucosal trigger zones: washing the face, shaving, tooth brushing, eating, talking, or a cold breeze.
• Diagnostic Distinction: In classical trigeminal neuralgia, the neurological sensory examination is completely normal. The presence of sensory loss (numbness, hypoaesthesia) indicates secondary trigeminal neuralgia (e.g., multiple sclerosis plaque or acoustic neuroma compressing the nerve root), requiring urgent brain MRI.
• Differentiation from Odontogenic Pain: Unlike acute pulpitis, trigeminal neuralgia pain is non-continuous, is not provoked by thermal liquids, lacks periapical radiographic pathology, and follows discrete refractory cycles.
• Management: Medical first-line therapy is Carbamazepine (100 mg twice daily, titrated up to 800–1200 mg daily; monitor full blood count for agranulocytosis and liver function). Surgical treatment: Microvascular Decompression (Jannetta procedure) via posterior fossa craniotomy to lift an aberrant arterial loop (most commonly the superior cerebellar artery) compressing the trigeminal root entry zone at the pons.

Bell's Palsy

Bell's palsy is an acute, isolated, idiopathic Lower Motor Neurone (LMN) paralysis of the facial nerve (CN VII):

• Clinical Signs: Rapid onset (peaks within 48 hours) of complete unilateral facial weakness:
  • Inability to raise the eyebrow or wrinkle the ipsilateral forehead (frontalis paralysis).
  • Inability to close the eye (orbicularis oculi paralysis); on attempted closure, the eyeball rolls upward and outward (Bell's phenomenon).
  • Drooping of the corner of the mouth, loss of the nasolabial fold, drooling of saliva, and flattening of the cheek (buccinator/orbicularis oris paralysis).
  • Hyperacusis (loss of stapedius muscle dampening) and loss of taste on the anterior two-thirds of the tongue (chorda tympani involvement).
• UMN vs LMN Facial Nerve Palsy: In an Upper Motor Neurone lesion (e.g., Stroke), the muscles of the upper face (forehead and eye closure) are spared because the dorsal portion of the facial motor nucleus in the pons receives bilateral corticonuclear innervation from both cerebral hemispheres. In an LMN lesion (Bell's palsy), the final common motor pathway is severed, causing complete paralysis of the entire ipsilateral face, including the forehead.
• UK Treatment Guidelines (NICE): Prescribe early high-dose oral corticosteroids: Prednisolone 50 to 60 mg daily for 10 days, initiated within 72 hours of symptom onset to reduce perineural oedema within the narrow osseous facial canal.
• Corneal Protection: The primary complication is exposure keratitis, corneal ulceration, and permanent blindness due to the inability to blink or close the eye. The dentist/doctor must prescribe lubricating eye drops (artificial tears) by day, ophthalmic lubricating ointment at night, and instruct the patient to tape the eyelid closed or wear an eye patch while sleeping.

Giant Cell Arteritis (Temporal Arteritis)

Giant cell arteritis (GCA) is a systemic granulomatous panarteritis of medium- and large-sized arteries, preferentially targeting extracranial branches of the carotid arteries (superficial temporal, ophthalmic, and facial arteries):

• Demographics: Occurs exclusively in patients over 50 years of age (median age 75); strong association with polymyalgia rheumatica (stiffness in shoulder and pelvic girdles).
• Pathognomonic Triad:
  1. Severe, new-onset unilateral temporal or occipital headache.
  2. Scalp tenderness: Severe pain elicited by simple tactile contact, such as combing hair or resting the head on a pillow.
  3. Jaw Claudication: Occurs in ~50% of patients. Severe fatigue, aching, or cramping pain in the masseter and temporalis muscles provoked specifically by mastication or continuous talking, which rapidly resolves upon resting the jaw. It is caused by reversible ischaemia in the branches of the maxillary artery supplying the masticatory apparatus.
• The Catastrophic Hazard — Irreversible Blindness: Occlusion of the posterior ciliary arteries (branches of the ophthalmic artery) produces Anterior Ischaemic Optic Neuropathy (AION), resulting in sudden, painless, permanent, irreversible blindness in the affected eye, which can spread to the contralateral eye within hours to days.
• Investigations: Profoundly elevated inflammatory markers: Erythrocyte Sedimentation Rate (ESR) typically $> 50-100\text{ mm/hr}$ and elevated C-Reactive Protein (CRP). Definitive diagnosis: Temporal Artery Biopsy (TAB) demonstrating transmural granulomatous infiltrate with multinucleated giant cells and fragmentation of the internal elastic lamina.
• Emergency Dental Action: Giant cell arteritis is a medical ophthalmic emergency. If a dental patient presents with new temporal headache and jaw claudication, the dentist must immediately refer the patient to the emergency eye hospital or acute rheumatology service on the same day. High-dose systemic corticosteroids (oral Prednisolone 60 mg daily, or IV methylprednisolone) MUST be commenced immediately without waiting for biopsy results to preserve vision.

4. Clinical Traps, Diagnostic Pitfalls, and Worked Scenarios

[!CAUTION] Clinical Trap: Misdiagnosing Jaw Claudication as Temporomandibular Disorder (TMD): A 74-year-old female presents with bilateral pain in her masticatory muscles when chewing hard foods. The practitioner palpates tender masseter muscles and diagnoses myofascial pain dysfunction syndrome (TMD), fitting an acrylic occlusal splint. Two weeks later, the patient wakes up completely blind in her right eye. A detailed history would have revealed severe scalp tenderness when brushing her hair and a continuous right temporal headache. In any patient over 50 presenting with "jaw pain when chewing", giant cell arteritis must be actively excluded before diagnosing TMD.

[!WARNING] Clinical Trap: Dental Extractions in Undetected Severe Liver Cirrhosis: Performing routine dental extractions on a patient with chronic alcoholic cirrhosis without a recent clotting screen and full blood count is hazardous. Severe deficiency of hepatic clotting factors (II, VII, IX, X) combined with hypersplenism-induced thrombocytopenia and impaired fibrinogen synthesis can result in intractable, life-threatening post-extraction haemorrhage. In suspected liver impairment, always obtain a current INR, APTT, and platelet count, and have local haemostatic agents readily available.

Worked Clinical SBA Scenario

Scenario: A 76-year-old female presents to your dental surgery complaining of severe, cramp-like pain in both cheeks and temples that develops after approximately two minutes of chewing solid food, forcing her to pause eating until the discomfort subsides. She also notes a persistent right-sided throbbing headache over the past three weeks and states that brushing her hair has become intensely painful. Palpation reveals a prominent, tender, non-pulsatile cord-like swelling over the right superficial temporal artery. There is no joint clicking or TMJ tenderness.

Question: What is the most likely diagnosis, what catastrophic complication is imminent, and what is the immediate management required of the dental practitioner?

Analysis and Clinical Governance: The clinical presentation of jaw claudication provoked by chewing solid food, combined with severe scalp tenderness when brushing hair and a unilateral temporal headache in a patient over 50 years of age, is classic for Giant Cell Arteritis (Temporal Arteritis). The non-pulsatile, tender temporal artery reflects transmural granulomatous panarteritis. The most catastrophic risk is irreversible, permanent visual loss due to ischaemic optic neuropathy from posterior ciliary arterial occlusion. The dentist must recognize this as an acute medical emergency and arrange immediate same-day referral to an emergency ophthalmology department or acute medical team, ensuring high-dose oral corticosteroid therapy (Prednisolone 60 mg daily) is initiated immediately to safeguard the patient's vision.