Patterns of pain-free response in 497 cases of classic trigeminal neuralgia treated with Gamma Knife surgery and followed up for least 1 year
Authors: Tuleasca Constantin , Carron Romain , Resseguier Noémie , Donnet Anne , Roussel Philippe , Gaudart Jean , Levivier Marc , Régis Jean 
Published: November 2018

Object
The goal of this study was to establish whether clear patterns of initial pain freedom could be identified when treating patients with classic trigeminal neuralgia (TN) by using Gamma Knife surgery (GKS). The authors compared hypesthesia and pain recurrence rates to see if statistically significant differences could be found.

Methods
Between July 1992 and November 2010, 737 patients presenting with TN underwent GKS and prospective evaluation at Timone University Hospital in Marseille, France. In this study the authors analyzed the cases of 497 of these patients, who participated in follow-up longer than 1 year, did not have megadolichobasilar artery– or multiple sclerosis–related TN, and underwent GKS only once; in other words, the focus was on cases of classic TN with a single radiosurgical treatment. Radiosurgery was performed with a Leksell Gamma Knife (model B, C, or Perfexion) using both MR and CT imaging targeting. A single 4-mm isocenter was positioned in the cisternal portion of the trigeminal nerve at a median distance of 7.8 mm (range 4.5–14 mm) anterior to the emergence of the nerve. A median maximum dose of 85 Gy (range 70–90 Gy) was delivered. Using empirical methods and assisted by a chart with clear cut-off periods of pain free distribution, the authors were able to divide patients who experienced freedom from pain into 3 separate groups: patients who became pain free within the first 48 hours post-GKS; those who became pain free between 48 hours and 30 days post-GKS; and those who became pain free more than 30 days after GKS.

Results
The median age in the 497 patients was 68.3 years (range 28.1–93.2 years). The median follow-up period was 43.75 months (range 12–174.41 months). Four hundred fifty-four patients (91.34%) were initially pain free within a median time of 10 days (range 1–459 days) after GKS. One hundred sixty-nine patients (37.2%) became pain free within the first 48 hours (Group PF≤ 48 hours), 194 patients (42.8%) between posttreatment Day 3 and Day 30 (Group PF(>48 hours, ≤ 30 days)), and 91 patients (20%) after 30 days post-GKS (Group PF>30 days). Differences in postoperative hypesthesia were found: in Group PF≤ 48 hours 18 patients (13.7%) developed postoperative hypesthesia, compared with 30 patients (19%) in Group PF(>48 hours, ≤ 30 days) and 22 patients (30.6%) in Group PF>30 days (p = 0.014). One hundred fifty-seven patients (34.4%) who initially became free from pain experienced a recurrence of pain with a median delay of 24 months (range 0.62–150.06 months). There were no statistically significant differences between the patient groups with respect to pain recurrence: 66 patients (39%) in Group PF≤ 48 hours experienced pain recurrence, compared with 71 patients (36.6%) in Group PF(>48 hours, ≤ 30 days) and 27 patients (29.7%) in Group PF>30 days (p = 0.515).

Conclusions
A substantial number of patients (169 cases, 37.2%) became pain free within the first 48 hours. The rate of hypesthesia was higher in patients who became pain free more than 30 days after GKS, with a statistically significant difference between patient groups (p = 0.014).