Painful Grimace Threshold
This is the level of painful stimulation at which a person will make a painful grimace expression with their facial muscles. (The author found it to be reduced in some fibromyalgia patients, for example when they were pressed on their right epicondylar tender points. The epicondyles are known to be among the most sensitive and specific tender points for testing fibromyalgia. (Tastekin N, Uzunca K, Sut N, Birtane M, Mercimek OB. Discriminative value of tender points in fibromyalgia syndrome. Pain Med 2010;11:466–71.) There are no known published studies using painful grimace thresholds. The whole subject of facial expression of pain is somewhat under-researched. In principle it could be studied with any painful tactile stimulus that can be applied safely in a graded manner. This is possible with a device called the Woodpecker which has a rubber tip that can be applied to a trapezius, olecranon and many other tender points. Further study would be needed to determine if the same could be said for heat pain, cold pain, electrical stimulation pain or laser pain.