The enigma of the interconnection of trigeminal pain and cranial autonomic symptoms.

Abstract

In this issue of Cephalalgia, two papers by Dr Benoliel and colleagues highlight the clinical profile of patients with trigeminal neuralgia (TN) and make two main observations: The electric-like stabbing pain attacks can be distinguished in a shorter and longer version (1) and longer attacks are a negative prognostic factor for treatment (2). This is remarkable for two reasons: It allows us to perhaps stratify patients before starting medical treatment, and secondly, because the authors also focused on other clinical signs including the phenomenon of cranial autonomic symptoms, it touches on the issue of the differentiation between TN of the ophthalmic division and short-lasting trigeminalautonomic headaches, namely short-lasting unilateral neuralgiform headache with conjunctival injection and tearing (SUNCT) and short-lasting unilateral neuralgiform headache attacks with cranial autonomic symptoms (SUNA) (3–5). In the first manuscript (1), the authors investigated 81 patients with the diagnosis of TN following the International Headache Society’s published classification (6) and focused on clinical features such as autonomic signs, persistent background pain, attack duration and reports of pain-related awakening. They found that quite a substantial subgroup had rather long attacks, and when dividing the cohort into groups with short attacks ( 2 minutes, n1⁄4 61) and long attacks (>2 minutes, n1⁄4 20), the short (duration) attack group fit most of the criteria for classical trigeminal neuralgia (CTN) while the long attack group did not. The authors’ use of the International Classification of Headache Disorders (ICHD) illustrates a fundamental complexity reminiscent of the entire diagnostic system: In the absence of biological markers, phenotype drives diagnosis; thus the diagnostic categories used may be called into question absent other markers. Moreover, as the authors mention in the Methods, atypical symptomatology was permitted to facilitate the study. A substantial confounding issue then becomes whether this was a study of TN or of a mixture of syndromes. A further substantial concern regarding cranial autonomic symptoms is the issue of whether it is their presence or prominence that is important. While both groups did not differ in pain severity, quality and location, the frequency of persistent background pain was significantly higher in the long (70%) compared to the short attack group (39%). The presence of persistence may be no more than a by-product of attack length, i.e. with longer attacks central sensitizing or neuropathic mechanisms may be more likely to be activated. Notably, there were no significant differences in the frequency of autonomic signs between both cohorts (2). Building on these findings, the authors then enrolled 81 patients prospectively and stratified them regarding attack duration. All patients were treated using standardized pharmacotherapeutic protocols and a treatment outcome, with a 50% reduction was considered significant. Clinical improvement was significantly more frequent in the short (74%) than in the long attack group (50%). Additionally, in the short attack group, patients with a longer disease duration and the presence of autonomic signs had a significantly poorer treatment response than patients with a shorter disease duration and no autonomic signs (2). Should these findings be replicated, they are certainly highly interesting for clinicians seeking a way to at least in part predict whether a medical treatment may be useful and how high or low the threshold for neuromodulatory treatments, such as thermocoagulation, should be in a particular patient. It also sheds light on the disease as such and allows us to perhaps clinically distinguish these patients better. Are patients