BackgroundShort-lasting unilateral neuralgiform headache attacks with conjunctival injection and tearing (SUNCT) and short-lasting unilateral neuralgiform headache attacks with cranial autonomic symptoms (SUNA) are two rare headache syndromes classified broadly as Trigeminal Autonomic Cephalalgias (TACs).MethodsHere, 65 SUNCT (37 males) and 37 SUNA (18 males) patients were studied to describe their clinical manifestations and responses to treatment.ResultsPain was almost always unilateral and side-locked. There were three types of attack: Single stabs, stab groups, and a saw-tooth pattern, with some patients experiencing a mixture of two types. As to cranial autonomic symptoms, SUNA patients mainly had lacrimation (41%) and ptosis (40%). Most cases of the two syndromes had attack triggers, and the most common triggers were touching, chewing, or eating for SUNCT, and chewing/eating and touching for SUNA. More than half of each group had a personal or family history of migraine that resulted in more likely photophobia, phonophobia and persistent pain between attacks. For short-term prevention, both syndromes were highly responsive to intravenous lidocaine by infusion; for long-term prevention, lamotrigine and topiramate were effective for SUNCT, and lamotrigine and gabapentin were efficacious in preventing SUNA attacks. A randomized placebo-controlled cross-over trial of topiramate in SUNCT using an N-of-1 design demonstrated it to be an effective treatment in line with clinical experience.ConclusionsSUNCT and SUNA are rare primary headache disorders that are distinct and very often tractable to medical therapy.

Introduction: Abuse of nitrous oxide (N 2 O) has an unusually high lifetime prevalence in developed countries and represents a serious concern worldwide. Myeloneuropathy following the inhalant abuse is commonly attributed to the disturbance of vitamin B12 metabolism, with severe motor deficits are often noted. The present study aims to elucidate its underlying pathophysiology. Methods: Eighteen patients with N 2 O abuse or vitamin B12 deficiency were recruited. Comprehensive central and peripheral neuro-diagnostic tests were performed, including whole spine MRI, and thermal quantitative sensory testing (QST). Specifically, paired motor and sensory nerve excitability tests were performed in order to obtain a complete picture of the sensorimotor axonal damage. Results: The mean duration of N 2 O exposure for the N 2 O abuse patients was 17.13 ± 7.23 months. MRI revealed T2 hyperintensity in 87.5% of the N 2 O abuse patients and 50% of the vitamin B12 deficiency patients. In N 2 O abuse patients, the motor nerve excitability test showed decreased in peak response (7.08 ± 0.87 mV, P = 0.05), increased latency (7.09 ± 0.28 ms, P < 0.01), increased superexcitability (−32.95 ± 1.74%, P < 0.05), and decreased accommodation to depolarizing current [TEd (40–60 ms) 56.53 ± 0.70%, P < 0.05]; the sensory test showed only decreased peak response (30.54 ± 5.98 μV, P < 0.05). Meanwhile, motor test in vitamin B12 deficiency patients showed only decreased accommodation to depolarizing current [TEd (40–60 ms) 55.72 ± 1.60%, P < 0.01]; the sensory test showed decreased peak response (25.86 ± 3.44 μV, P < 0.05) increased superexcitability (−28.58 ± 3.71%, P < 0.001), increased subexcitability (8.31 ± 1.64%, P < 0.05), and decreased accommodation to depolarizing current [TEd (peak) 67.31 ± 3.35%, P < 0.001]. Conclusion: Compared to vitamin B12 deficiency, N 2 O abuse patients showed prominent motor superexcitability changes and less prominent sensory superexcitability changes, hinting a unique pathological process different from that of vitamin B12 deficiency. N 2 O abuse might cause axonal dysfunction not only by blocking methionine metabolism but also by toxicity affecting the paranodal region.