Quantitative assessment of facial muscle impairment in patients with hemispheric stroke

Facial weakness is frequently observed in patients with hemispheric stroke. Most reports refer to qualitative assessment. The aim was to quantify the upper and lower facial muscle function in patients with hemispheric stroke. Three different facial expressions (forced smile, posed smile and maximum eyebrow lift) and facial rest position were mapped using a 3D video system. Twenty-seven patients with hemispheric stroke (PG) and 22 controls (CG) were recruited. Facial asymmetry was expressed as absolute side differences between four corresponding distances. In PG, a longer distance was found from inner canthus to oral commissure (dist1) on the impaired side in all investigated poses (PG non-affected-affected side: range of all poses 1·18 ± 4·45 to 1·80 ± 2·37 mm; CG right-left side: range -0·69 ± 1·55 to -0·43 ± 1·39 mm, Mann-Whitney tests: 0·0002 < P < 0·0423). In addition, the ratio of the impaired to the non-affected side was different in PG for dist1 in rest and eyebrow lift (Wilcoxon tests: 0·0011 < P < 0·0288). CG showed asymmetries in rest and forced smile (Wilcoxon tests: P = 0·0392 and P = 0·0424). Furthermore, dist1 in PG showed higher variances than in CG (F-tests: 0·0001 < P < 0·0445) except for the relative dist1 at rest (F-test: P = 0·0533). The distance between inner eyebrow corner and inner canthus showed no side difference in both groups during eyebrow lift (n.s.); nevertheless, two patients showed distinct asymmetries. The employed 3D video system proved sensitive in assessing facial muscle function. The results confirm and quantify that the lower facial muscles are more affected by hemispheric stroke than the upper ones and show that the measured distances were more variable in post-stroke patients than in control subjects.