What is the differential diagnosis and treatment approach for a patient presenting with symptoms of Short-lasting Unilateral Neuralgiform headache with Autonomic symptoms (SUNA) versus Trigeminal Neuralgia?

SUNA vs Trigeminal Neuralgia: Differential Diagnosis and Treatment

Key Distinguishing Feature

The critical distinction is the presence of autonomic symptoms: SUNA/SUNCT present with prominent autonomic features (tearing, conjunctival injection, rhinorrhea, nasal blockage, facial redness, ear fullness) alongside pain, while classical trigeminal neuralgia does not have autonomic features. 1

Differential Diagnostic Algorithm

Step 1: Assess Attack Frequency and Refractory Period

Trigeminal Neuralgia:

• Paroxysmal attacks lasting seconds to minutes with mandatory refractory periods between attacks where pain cannot be triggered 1, 2
• Pain-free intervals are obligatory between episodes 3

SUNA/SUNCT:

• Rapid attacks lasting seconds to several minutes with up to 200 attacks daily and NO refractory period between attacks 1, 2
• Attacks can occur in rapid succession without pain-free intervals 1

Step 2: Identify Autonomic Features

This is the most critical differentiating factor. 1

SUNA/SUNCT autonomic symptoms include:

• Conjunctival injection (red eye) 1
• Tearing/lacrimation 1
• Rhinorrhea 1
• Nasal blockage 1
• Facial redness 1
• Ear fullness 1

Trigeminal neuralgia:

• Does NOT typically cause visible inflammation, swelling, or autonomic features in its classical form 1
• Primarily manifests as a pure pain syndrome 1

Common pitfall: Recent evidence shows that 12% of patients diagnosed with trigeminal neuralgia may actually have autonomic symptoms that were not adequately assessed, suggesting SUNA/SUNCT may be underdiagnosed 4. Always specifically ask about and examine for tearing, eye redness, and nasal symptoms.

Step 3: Characterize Pain Quality and Distribution

Both conditions share:

• Sharp, shooting, electric shock-like quality 1, 2
• Unilateral presentation 2
• Trigger sensitivity (light touch, washing face, eating, brushing teeth) 3, 5

SUNA/SUNCT distribution:

• Mainly affects first and second trigeminal divisions (V1/V2) 1

Trigeminal neuralgia distribution:

• Most commonly affects V2 (maxillary) and V3 (mandibular) branches 2

Step 4: Evaluate for Red Flags Requiring Urgent MRI

Obtain MRI immediately if:

• Sensory deficits in trigeminal distribution (suggests tumor, MS, or structural lesion) 1, 2, 3
• Continuous pain from onset (not typical paroxysmal pattern) 1, 3
• Bilateral symptoms (highly atypical for either condition) 3
• Motor weakness in muscles of mastication (suggests secondary cause) 2

MRI protocol: Use 3D heavily T2-weighted sequences combined with MRA to identify neurovascular compression (83-100% congruence with surgical findings) and include pituitary fossa views if SUNCT/SUNA is suspected 1, 2

Treatment Approach

Trigeminal Neuralgia Treatment

First-line therapy:

• Carbamazepine is the gold standard 1, 2, 6
• Starting dose: 100 mg twice daily (200 mg/day) 6
• Increase by 200 mg/day at weekly intervals using 3-4 times daily dosing 6
• Maintenance: 400-800 mg daily, maximum 1200 mg/day 6
• Alternative: Oxcarbazepine is equally effective with fewer side effects 1, 2

Second-line options when carbamazepine fails or is not tolerated:

• Lamotrigine 2
• Baclofen 2
• Gabapentin combined with ropivacaine 2
• Pregabalin 2

Surgical intervention:

• Obtain neurosurgical consultation early when medications become ineffective or intolerable 2
• Microvascular decompression (MVD) is preferred for patients with documented neurovascular compression on MRI without significant comorbidities 2
• MVD efficacy: 70% pain-free at 10 years, with 2-4% hearing loss risk and 0.4% mortality 2

SUNA/SUNCT Treatment

The efficacy of conventional treatments is disappointing and challenging for SUNA/SUNCT. 5

First-line preventive therapy:

• Lamotrigine is effective in approximately two-thirds of patients with SUNA/SUNCT 5
• This is the primary difference from trigeminal neuralgia, where carbamazepine is first-line 5

Acute exacerbation management:

• Intravenous lidocaine is essential for management of acute exacerbation of intractable pain 5

Secondary preventive options:

• Topiramate 5
• Oxcarbazepine 5
• Gabapentin 5
• Botulinum toxin in selective cases 5

Surgical approaches for refractory cases:

• Neurovascular decompression (commonly observed in SUNA/SUNCT) 5
• Deep brain stimulation has shown efficacy in recent case series for refractory SUNCT/SUNA 7

Critical Clinical Pearls

Why this distinction matters clinically:

• Carbamazepine (first-line for TN) has disappointing efficacy in SUNA/SUNCT 5
• Lamotrigine (first-line for SUNA/SUNCT) is only second-line for TN 2, 5
• Misdiagnosis leads to treatment failure and unnecessary medication trials 4

The most common diagnostic error: Failing to specifically assess for autonomic symptoms in patients presenting with trigeminal distribution pain, leading to misdiagnosis of SUNA/SUNCT as trigeminal neuralgia 4. Always examine the eye for injection and tearing during or immediately after an attack, and specifically ask about nasal symptoms.