What is the most likely diagnosis for a 30-year-old female with acute facial pain on teeth brushing, unresponsive to analgesics (pain medications), and internuclear ophthalmoplegia, with abnormal Magnetic Resonance Imaging (MRI) findings?

Multiple Sclerosis/Demyelinating Syndrome

The most likely diagnosis is multiple sclerosis (MS) or another demyelinating syndrome (option c), as the combination of trigeminal neuralgia-like facial pain triggered by teeth brushing, internuclear ophthalmoplegia (INO), and abnormal MRI findings in a 30-year-old woman creates a classic presentation for MS. 1, 2

Why This Diagnosis is Most Likely

Internuclear Ophthalmoplegia as the Key Localizing Sign

• INO is caused by a lesion in the medial longitudinal fasciculus (MLF) in the brainstem, and MS is one of the two most common causes (along with stroke), accounting for 34% of all INO cases in large series 2, 3
• In younger patients (age 20-40), MS becomes the predominant cause of INO, as stroke is less likely in this age group 1, 3
• Bilateral INO is particularly suggestive of MS (occurring in 73% of MS-related INO cases versus only 13% of stroke-related cases), though the question doesn't specify laterality 3
• The abnormal MRI finding strongly supports a demyelinating process, as MRI showing demyelination plaques is a key diagnostic criterion for MS 4, 1

Facial Pain Pattern Consistent with MS-Related Trigeminal Neuralgia

• Trigeminal neuralgia is a well-recognized oral manifestation of MS, presenting as paroxysmal sharp pain triggered by light touch activities like brushing teeth 5, 4
• The pain being unresponsive to analgesics is characteristic of trigeminal neuralgia, which requires anticonvulsants (carbamazepine or oxcarbazepine) rather than standard pain medications 5
• MS patients commonly present with trigeminal neuralgia, paresthesia, or orofacial pain as part of their symptom complex 4
• In rare cases, trigeminal neuralgia is symptomatic of MS rather than the classic neurovascular compression etiology 5

Demographic and Clinical Context

• MS typically presents in young adults with mean age of onset 20-30 years, making this 30-year-old patient's age ideal for MS presentation 1
• MS more commonly affects women with a female-to-male ratio of nearly 3:1 1
• MS commonly presents with brainstem syndromes such as INO developing over several days, along with other neurological manifestations 1

Why Other Options Are Less Likely

Eagle's Syndrome (Option a)

• Eagle's syndrome involves elongated styloid process causing pharyngeal pain, typically with dysphagia and odynophagia, not associated with INO or abnormal brain MRI 5

Migraine (Option b)

• While migraine can cause facial pain, it does not cause INO or the specific MRI abnormalities seen in demyelinating disease 5
• Migraine pain typically responds to analgesics and triptans, unlike this patient's refractory pain 5

Trigeminal Neuralgia Alone (Option d)

• While the facial pain pattern fits trigeminal neuralgia, isolated trigeminal neuralgia does not explain the INO 5
• MRI is indicated in trigeminal neuralgia to exclude MS, tumors, or neurovascular compression, suggesting that when MRI is abnormal with concurrent INO, the underlying diagnosis is likely MS 5, 6

TMJ Dysfunction (Option e)

• TMJ disorders cause continuous or intermittent pain in the jaw joint and muscles of mastication, not the sharp, electric shock-like pain triggered by light touch that characterizes trigeminal neuralgia 5, 7
• TMJ dysfunction does not cause INO or abnormal brain MRI findings 5, 7

Diagnostic Confirmation

• Diagnosis of MS is made using the 2017 McDonald Criteria, which combines clinical signs/symptoms, MRI T2 lesions, and cerebrospinal fluid-specific oligoclonal bands 1
• The presence of MRI lesions at the brainstem level affecting the medial pontine tegmentum would explain both the INO and support MS diagnosis 8
• MRI is the method of choice for diagnostic imaging of MLF lesions in patients with INO 2

Critical Management Implications

• Treatment of acute MS relapses includes high doses of corticosteroids, while long-term management requires disease-modifying therapies 4, 1
• The facial pain component should be treated with anticonvulsants (carbamazepine or oxcarbazepine as first-line) rather than standard analgesics 5
• Nine classes of disease-modifying therapies are available for relapsing-remitting MS, which can reduce annual relapse rates by 29-68% 1