SUNA Syndrome

SUNA syndrome is short lasting unilateral neuralgiform headache attacks with cranial autonomic symptoms. It is a subtype of the same spectrum as SUNCT, in which only one or neither of conjunctival injection and tearing is present, with another cranial autonomic feature.

It is very rare, with an estimated prevalence of about 1 in 100,000. It starts at a mean age of about 50 years, with a slight male predominance.

Pattern of attacks. Attacks last 1 to 600 seconds, occur at least once daily for more than half the time, and are often triggered by touch, chewing or washing. Single stabs, groups and saw tooth patterns occur.

Secondary causes. Posterior fossa tumours, pituitary lesions, trigeminal neurovascular compression and brainstem lesions can cause identical attacks, so imaging is needed.

Pathophysiology.

The mechanisms are shared with SUNCT: activation of the trigeminal autonomic reflex with hypothalamic involvement.

Cutaneous triggers suggest trigeminal root sensitisation.

• Brief stabbing or shooting pain of the orbital, supraorbital or temporal region lasting 1 to 600 seconds, often 1 to 100 or more each day.
• At least one ipsilateral cranial autonomic feature (nasal congestion, rhinorrhoea, eyelid oedema, forehead sweating, ptosis or miosis), with conjunctival injection and tearing either absent or only one present.
• Cutaneous triggers in the trigeminal area and neck movement triggers.
• Absent response to indomethacin.

Red flags.

• Neurological deficit, sensory loss or visual symptoms.
• Abnormal pituitary function or MRI.
• Onset in a young person or rapid progression.

• ICHD-3 criteria: at least 20 attacks of moderate to severe unilateral pain lasting 1 to 600 seconds, with at least one cranial autonomic symptom, not meeting criteria for SUNCT.
• MRI of the brain with contrast and attention to the pituitary, posterior fossa and trigeminal nerve; MR angiography for neurovascular compression.
• Pituitary hormone testing when relevant; exclude trigeminal neuralgia and dental or sinus disease.
• Headache diary of attack frequency and duration.

Differential diagnosis. SUNCT, trigeminal neuralgia, paroxysmal hemicrania, cluster headache, hemicrania continua and secondary headache.

• Preventive drugs are required because attacks are too brief for acute treatment.
• Lamotrigine, first line: 25 mg orally once daily for 2 weeks, then 50 mg daily for 2 weeks, then increases of 50 mg every 1 to 2 weeks to a usual 100 to 200 mg daily in 2 divided doses. Maximum 400 mg daily. Monitor for rash, hypersensitivity and Stevens-Johnson syndrome (stop at the first rash). Reduce dose in moderate to severe hepatic impairment; reduce the titration rate with valproate; levels fall with oestrogen containing contraception and in pregnancy.
• Topiramate 25 mg orally at night, increased by 25 mg weekly to a usual 100 to 200 mg daily in 2 divided doses. Maximum 400 mg daily. Review at 3 months and stop if there is no benefit. Monitor bicarbonate, mood, weight, kidney stones and visual symptoms. Halve the dose when creatinine clearance is under 70 mL/min; contraindicated in pregnancy and effective contraception is needed.
• Gabapentin 300 mg orally at night on day 1, 300 mg twice daily on day 2, then 300 mg three times daily on day 3, increased by 300 mg every 3 to 7 days to 900 to 2400 mg daily in 3 divided doses. Maximum 3600 mg daily. Review at 4 to 8 weeks and stop if there is no meaningful benefit. Monitor sedation, dizziness, peripheral oedema, mood and misuse. Adjust for renal function: creatinine clearance 50 to 79 mL/min, 600 to 1800 mg daily; 30 to 49 mL/min, 300 to 900 mg daily; 15 to 29 mL/min, 150 to 600 mg daily; under 15 mL/min, 150 to 300 mg daily. Avoid in pregnancy unless benefit outweighs risk.
• Greater occipital nerve block, neuromodulation or other specialist treatments for refractory attacks.
• Treat identified secondary causes; neurosurgical review for neurovascular compression.

Monitoring. Review at 4 to 6 weeks and every 3 months; track attack frequency; review rash and drug effects.

Referral and escalation. Headache specialist for all patients; neurosurgery for secondary causes.

Special groups. Pregnancy: avoid topiramate and plan with specialists. Older adults: slower titration and lower gabapentin doses.