SUNCT Syndrome: Short-acting Unilateral Neuralgiform headache with Conjunctival injection and Tearing
The trigeminal autonomic cephalgias (TACs) are primary headaches characterized by short episodes of unilateral pain in the trigeminal distribution accompanied by ipsilateral autonomic symptoms.  The TACs include cluster headaches, paroxysmal hemicrania, hemicrania continua, and short-lasting unilateral neuralgiform headache attacks. Of all the TACs, short-lasting unilateral neuralgiform headache attacks are the shortest in duration and the highest in frequency and can be further classified into SUNA (Short-lasting unilateral neuralgiform headache attacks with cranial autonomic symptoms) and SUNCT syndromes. Short-lasting unilateral neuralgiform with conjunctival injection and tearing (SUNCT) is the least common of the TACs.
SUNCT was first reported in 1978 and fully characterized in 1989. In 2004, SUNCT was added to the International Classification of Headache Disorders, along with SUNA. Together, they were both classified as subtypes of short lasting unilateral neuralgiform headache attacks in 2013.
SUNCT is an uncommon headache syndrome but the estimated prevalence is 6.6 per 100,000 and an annual incidence is 1.2 per 100,000. This estimate may be under-representative of the true incidence.
The majority of SUNCT patients age of onset between 35 and 65 years, with a mean age of 48 years. However, cases as young as 10-years-old and as old as 77-years-old have been described. SUNCT may have a male predominance.
The autonomic features of SUNCT are thought to result from activation of trigeminal autonomic reflex (TAR). The reflex is a physiologic pathway that connects the trigeminal nerve and facial cranial nerve sympathetic flow in the brainstem. Input from the trigeminal nerve to the parasympathetic fibers of the superior salivatory nucleus (SSN) may be a part of the mechanisms of SUNCT. The SSN innervates the nasal, lacrimal, submandibular, and sublingual glands, and palate, thus leading to the typical trigeminal autonomic symptoms of conjunctival injection, rhinorrhea, miosis, ptosis, lacrimation, and facial sweating in SUNCT.
Functional MRI have shown ipsilateral activation of hypothalamic gray matter during episodes of SUNCT.    The hypothalamus is connected to the pain modulating system as well as the SSN, perhaps regulating both the pain and autonomic features of SUNCT. This has been further supported by few case reports of patients who achieved significant improvement following a deep brain stimulator (DBS) placement in the ipsilateral hypothalamus.
SUNCT may also have a vascular component.   Increased ictal intraocular pressure and corneal indentation pulse amplitudes suggest increased intraocular blood flow.   In addition recordings of abnormal phlebograms involving the superior ophthalmic vein and cavernous sinus on the side of the headache had been reported.
SUNCT is characterized by brief attacks of severe unilateral pain in the ocular/periocular region. Some cases have shown the pain to radiate to other regions of the head (temple, nose, cheek, and palate) but mainly are localized to the V1 ophthalmic division of the trigeminal nerve. The pain usually described as burning, stabbing, or electric with moderate to severe intensity. The presence of both conjunctival injection and lacrimation are diagnostic criteria of SUNCT, which become evident as the pain begins and disappears as the pain ends. Rhinorrhea and nasal congestion occur in two-thirds of cases. Subclinical increases in forehead sweating as well as intraocular pressure and corneal temperature have been described. Some patients have presented with ‘pseudoptosis’ due to vascular edema in the eyelids. Furthermore, two patients have been documented to have ipsilateral ptosis, miosis, and anhidrosis.
Patients can have mix of spontaneous or triggered attacks or an entirely spontaneous attack. Tactile stimulation of the forehead and orbit or usage of muscles of facial expression or mastication can trigger an attack. The duration of these attacks ranges from 1 to 600 seconds with a mean of 61 seconds. They can occur at any time of the day with no nocturnal tendency but have been found to predominate during daytime. Some cases have also seen a bimodal nature. SUNCT attacks can occur from 3 to 100 times a day with a mean of 28 episodes in a clustering pattern. The attacks can present differently among patients. For instance, a plateau profile describes a prolonged phase of sustained severe pain, lasting a few seconds, while a saw-tooth profile is a period of sustained pain with fluctuations in intensity but does not completely resolve in the course of the attack. Patients can experience attacks on a daily basis for several weeks and then have an attack-free period lasting for weeks to months before the next cluster. Between symptomatic periods, most patients usually have no additional symptoms but may experience a low-grade background pain or discomfort in the symptomatic area.
The diagnosis of SUNCT depends heavily on assessment of clinical features and differentiation of symptoms from other TACs.
- Lack of response to oxygen and indomethacin lowers cluster headaches, paroxysmal hemicrania, and hemicrania continua as a differential.
- Cluster headaches have a longer duration of symptoms compared to SUNCT.
- Trigeminal neuralgia present for shorter time intervals and are not accompanied by prominent ipsilateral autonomic features.
Imaging of the posterior and pituitary fossae may be necessary to rule out secondary SUNCT like presentations. The diagnosis of SUNCT, according to International Classification of Headache Disorders (IHS) 3rd edition (ICHD-3), requires all the following :
- A. At least 20 attacks fulfilling criteria B through D.
- B. Attacks of unilateral orbital, suborbital, or temporal stabbing or pulsating pain lasting 1-600 seconds.
- C. Pain is accompanied by ipsilateral conjunctival injection and lacrimation
- D. Attacks occur with a frequency of at least one a day
- E. Not better accounted for by another ICHD-3 Diagnosis
Although there is no single proven effective cure for SUNCT, symptoms can be treated with carbamazepine, oxcarbazepine, topiramate and gabapentin. Lamotrigine has also been used in SUNCT and there have been cases of response to intravenous lidocaine.
Surgical interventions such as percutaneous trigeminal ganglion compression, microvascular decompression of the trigeminal root (Jannetta procedure), and deep brain stimulation have shown success with complete remission. However, they should only be considered in cases refractory to pharmacological therapy. 
The natural history of SUNCT is recurrent attacks that have variable response to treatment.
Clinicians should be aware of SUNCT. Patients with SUNCT may present to ophthalmology because of the predilection for the trigeminal distribution and the presence of conjunctival redness and tearing. Referral to a neurologist for evaluation and treatment is recommended for SUNCT.
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