Short-lasting unilateral neuralgiform headache attacks with conjunctival injection and tearing (SUNCT syndrome) is a rare and debilitating primary headache disorder. It belongs to the group of conditions called Trigeminal Autonomic Cephalalgias (TACs), characterized by pain in the distribution of the trigeminal nerve accompanied by distinct involuntary symptoms. Understanding SUNCT requires grasping the severity of its presentation and the challenges involved in its diagnosis and management.
Prevalence and Epidemiological Data
SUNCT syndrome is the rarest of the Trigeminal Autonomic Cephalalgias (TACs), a group that includes the more common cluster headache. Epidemiological studies often group SUNCT with the related condition, SUNA (Short-lasting unilateral neuralgiform headache attacks with cranial autonomic symptoms), to gather sufficient data. The combined prevalence of these two disorders is estimated to be approximately 6.6 cases per 100,000 individuals.
The estimated annual incidence, or the number of new cases diagnosed each year, is very low, around 1.2 per 100,000 people. This suggests that SUNCT affects a very small fraction of the population, contributing to its obscurity in medical practice. Obtaining exact, standalone prevalence statistics for SUNCT alone is challenging due to the difficulties of studying such an uncommon disease.
The disorder typically presents later in life compared to other headache types, with the mean age of onset around 50 years (ranging from 35 to 65 years). There is a slight male predominance, with studies suggesting a male-to-female ratio of about 1.5 to 1. The small number of cases, coupled with misdiagnosis, suggests the true prevalence may be slightly higher than current estimates.
Defining Characteristics of SUNCT Attacks
The defining feature of SUNCT syndrome is the intensity and brevity of its attacks, which are centered on one side of the head and face. The pain is described as severe, often having a stabbing, burning, or electrical shock quality. This pain is typically localized to the eye, orbit, or temporal region, corresponding to the ophthalmic division of the trigeminal nerve.
The duration of individual pain episodes is remarkably short, lasting from five seconds up to a maximum of about four minutes (240 seconds). Attacks occur with extreme frequency, ranging from three to as many as 200 per day, with many patients averaging 60 episodes daily. This pattern of high frequency and short duration is unique among primary headache disorders.
The acronym SUNCT specifies the two mandatory cranial autonomic symptoms that occur on the same side as the pain: conjunctival injection (redness of the eye) and lacrimation (excessive tearing). Other accompanying symptoms include nasal congestion, a runny nose (rhinorrhea), and swelling of the eyelid (edema). These involuntary symptoms are triggered by the activation of the parasympathetic nervous system, which is linked to the trigeminal nerve pain pathway.
Diagnostic Criteria and Misidentification
Diagnosis of SUNCT syndrome is a clinical process, relying on a patient’s detailed description of symptoms and adherence to specific criteria established by the International Headache Society (ICHD-3). Formal diagnosis requires at least 20 attacks that meet the criteria for short-lasting unilateral pain accompanied by both ipsilateral conjunctival injection and lacrimation. The process also includes ruling out secondary causes, such as a structural lesion in the brain or pituitary gland, which can mimic SUNCT symptoms.
The rarity of SUNCT frequently leads to misidentification, causing delays in effective treatment. It is often mistaken for other TACs, most notably cluster headache, which also features unilateral pain and autonomic symptoms. A key difference is the attack duration: cluster headaches last significantly longer (from 15 minutes to three hours), compared to the seconds-long attacks of SUNCT.
Another common misdiagnosis is paroxysmal hemicrania (PH), which also features short, frequent attacks. The distinguishing factor is that PH is universally responsive to the anti-inflammatory drug indomethacin, while SUNCT is not. Given the precise treatment response required for each TAC, a specialized neurological consultation is necessary to correctly differentiate SUNCT from these other conditions.
Management and Treatment Approaches
Treatment of SUNCT syndrome focuses on prevention, as the attacks are often too brief for acute (“on-demand”) pain medications to be effective. The first-line prophylactic medication is typically the anticonvulsant Lamotrigine, which reduces the frequency and severity of attacks. Other preventative options include Topiramate and Gabapentin, which may be tried if Lamotrigine is ineffective or poorly tolerated.
These preventative medications work by stabilizing nerve pathways, particularly those involving sodium channels, which are implicated in the pain mechanism. For patients experiencing severe, sustained attacks, a short course of intravenous Lidocaine may be administered in a hospital setting to temporarily break the cycle of pain. This treatment can provide a profound, though temporary, improvement in a majority of patients.
In cases where pharmacological treatments fail to provide adequate relief, non-pharmacological or interventional procedures may be considered. Options include nerve blocks, although these have a lower success rate compared to oral medications. Surgical procedures, such as microvascular decompression, are reserved for the most refractory cases where a specific structural cause is identified, offering a last resort for managing this challenging disorder.