Refractory periods in SUNCT

Sir,

The refractory period in patients with SUNCT is studied by Pareja JA and group, and we deeply appreciate their contribution in today’s understanding of SUNCT. SUNCT has a resemblance with first division trigeminal neuralgia, but SUNCT can be distinguished by the presence of marked autonomic symptoms like conjunctival injection and tearing. However, we do not have clear understanding of the underlying pathophysiological divide between trigeminal neuralgia and SUNCT. Trigeminal autonomic reflex with central disinhibition of variable extent is believed to bring autonomic symptoms in an otherwise trigeminal neuralgia-like illness. So, the trigeminal neuralgia, SUNA and SUNCT may actually be a continuum [1]. It may still be worthwhile to differentiate trigeminal neuralgia from SUNCT, as the presence or absence of autonomic symptoms may actually point towards the underlying pathophysiology. However, trigeminal neuralgia (ophthalmic division) with florid autonomic features irrespective of refractory period as in our cases represents a spectrum of SUNCT [2]. Over a period of time, these patients may show variable attack severity and fluctuating duration of refractory period. Therefore, we referred to Cohn et al. [3] in our paper, not mistakenly though, as they recommended the application of absent refractory period to diagnostic criteria of SUNCT. We believe that refractory period may be present/relative in milder disease and may become absent with severe disease (saw tooth pattern or very frequent spontaneous attacks) [4, 5]. Once, refractory period is studied in a large cohort of SUNCT patients in respect to attack severity, disease chronicity, primary versus secondary disease or natural course versus on-medication course, it would be more authentic to apply absent refractory period to the diagnostic criteria of SUNCT.