Lip-length and snout indices: methods for quantitative assessment of peri-oral facial muscle strength.

Two simple bedside methods for the assessment of perioral muscle function are described. Using a marking gauge, the width of the mouth can be measured easily and accurately. Lip-length (LL) and snout (S) indices are expressions of the degree to which the width of the mouth can be lengthened or shortened. Facial muscle weakness as present in patients with various neuromuscular diseases results in low values for both indices. LL- and S-indices are measured by 3 observers in 19 healthy volunteers. Interobserver variation is negligible for the LL-index and large for the S-index. Intraobserver variation is moderate for both indices but slightly smaller for the LL- than for the S-index. The LL-index is suited for the assessment of changes in peri-oral musculature in longitudinal investigations.