Pain threshold in humans. A study with the pressure algometer.

Pain perception threshold (PPT) in the head was assessed with a pressure algometer in 40 control individuals (24 females and 16 males). Threshold was assessed at 11 symmetrical points on each side. The average threshold for each side was calculated, and differences between two sides were evaluated with an asymmetry index. Subjects were studied in relation to age and sex, and any difference in the symmetrical perception of pain on the head was registered. The deltoid muscle was chosen as a reference point, since it is rarely a site of trigger points. The reproducibility of the method was satisfactory. A significantly positive correlation was found between PPT value of the head and the deltoid muscle. There was no tendency to rise or fall in PPT during the same "session", which consisted of 3 separate complete measurements. The mean of mean values showed that there was little asymmetry as for the thresholds pertaining to the head in the total material. Age and sex apparently played little role as for the outcome of the test. The assessment of PPT in the head might be a useful tool in the study of lateralization of pain in unilateral headache syndromes.