Degree of praxis of command for facial muscles in healthy individuals to develop a new clinical scale for facial motor function in peripheral facial paresis

Abstract

Clinical scales evaluating facial motor function in peripheral facial paresis (PFP) have poor precision and evaluate only few muscle groups, making the assessment of the disorder and of potential therapeutic interventions difficult. It is likely that healthy subjects do not share the same degree of praxis for all facial movements. The main objective was to assess the degree of praxis for command to each muscle group innervated by the facial nerve (VII) in a healthy subject population, to select those to include in a new PFP clinical motor scale. Reliabilities of the praxis rating performance were also evaluated. This monocentric prospective study included video recordings of adult healthy subjects performing 23 bilateral facial movements, on both oral command and mime of the investigator. Primary endpoint was the degree of praxis rated ordinally with a 3-point scale (0 = total apraxia; 0.5 = partial praxis; 1 = perfect praxis). Each video was assessed twice by each rater four days apart. Intra- and inter-rater reliabilities were evaluated via kappa coefficients. Facial muscles were selected through a threshold of perfect praxis set at 80% of the total praxis in the sample, also taking into account reliability findings and clinical relevance. Facial video recordings of 50 healthy subjects (13 M; 37.1 ± 14.6 yo) were rated on two occasions by 3 PMR specialists (experience in PFP: 24.6 ± 31.0 months). Eleven muscle groups were characterized by a praxis greater than the 80% threshold; 4 muscle groups were between 70 and 80% and 8 below 70%. Intra- and inter-rater agreements were very strong (kappa coefficients > 0.60) for 10 and 14 muscle groups, respectively. Healthy individuals do not have the same degree of praxis on all facial muscle groups. Ten muscle groups were selected to be included in a new PFP clinical motor scale.