A multivariable prediction model for recovery patterns and time course of symptoms improvement in hemifacial spasm following microvascular decompression

Abstract

Background: Microvascular decompression (MVD) success rates exceed 90% in hemifacial spasm (HFS). However, postoperative recovery patterns and durations are variable.

Objective: We aim to study factors that might influence the postoperative patterns and duration needed until final recovery.

Method: Only patients following de-novo MVD with a minimum follow-up of 6 months were included. Overall trend of recovery was modeled. Patients were grouped according to recognizable clinical recovery patterns. Uni- and multivariable analyses were used to identify the factors affecting allocation to the identified patterns and time needed to final recovery.

Results: A total of 323 (92.6%) patients had > 90% symptom improvement, and 269 (77.1%) patients had complete resolution at the last follow-up. The overall trend of recovery showed steep remission within the first 6 months, followed by relapse peaking around 8 months with a second remission ~ 16 months. Five main recovery patterns were identified. Pattern analysis showed that evident proximal indentation of the facial nerve at root exit zone (REZ), males and facial palsy are associated with earlier recovery at multivariable and univariable levels. anterior inferior cerebellar artery (AICA), AICA/vertebral artery compressions and shorter disease durations are related to immediate resolution of the symptoms only on the univariable level. Time analysis showed that proximal indentation (vs. distal indentation), males and facial palsy witnessed significantly earlier recoveries.

Conclusion: Our main finding is that in contrast to peripheral indentation, proximal indentation of the facial nerve at REZ is associated with earlier recovery. Postoperative facial palsy and AICA compressions are associated with earlier recoveries. We recommend a minimum of 1 year before evaluating the final outcome of MVD for HFS.

Keywords: Delayed recovery; Hemifacial spasm; Microvascular decompression; Time course of recovery.

Fig. 1

Illustration of different arterial compressions at the root exit zone (REZ) causing proximal indentation/grooving at the brainstem (*) or distal indentation/grooving (arrowhead) just before starting the cisternal part. Facial nerve myelinated fibers shown from proximal to distal with transitional zone between central and peripheral myelin

Fig. 2

Endoscopic inspection with a 45° endoscope showing grooving/indentation of the facial nerve. A: proximal grooving at the brainstem (arrows). B: distal grooving where the nerve leaves the brainstem (arrows)

Fig. 3

Overall trend of postoperative symptoms resolution following MVD in HFS in our patients. Initial symptom severity in all patients was 100%. Follow-up beyond 8 years is not depicted on this graph

Fig. 4

Illustration sketch of the different patterns of symptoms resolution following MVD in HFS. The five groups: Group 1: immediate full resolution, Group 2: gradual full resolution, Group 3: eventual resolution, Group 4: initial full resolution with relapse(s) without final resolution and Group 5: improvement without full resolution and pie chart showing percentage distribution of each group in our patients

Fig. 5

Kaplan–Meier curves illustrate time to final resolution of the spasms following MVD for all patients and after stratification according to individual significant variables with comparison of the strata using the log rank test. A: for all patients without comparing any factors, B: sex (males and females), C: facial palsy yes/no, D: presence/absence of indentation/grooving of the nerve and its location and E: Forrest plot for independent factors affecting time to final recovery showing significance of sex, disease duration and location of the facial nerve grooving