THE REPRODUCIBILITY OF CEPHALIC PAIN PRESSURE THRESHOLDS IN CONTROL SUBJECTS AND HEADACHE PATIENTS

Pain pressure thresholds (PPT) were measured at 13 cephalic points bil aterally in 30 headache patients (la with tension-type headache, 10 wi th migraine and 10 with cervicogenic headache) and 10 central subjects on three different days, During the sessions, the subjects reported t heir pain intensity on the right and left sides of the head on a visua l analogue scale (VAS). The variability between daps was estimated as a coefficient of repeatability (CR=2 standard deviations of intraindiv idual differences). The mean CR across all 13 locations was larger in headache patients (2.0 kg/cm(2)) than in controls (1.68 kg/cm(2)). Var iability (CR) was larger in headache patients as compared to control s ubjects for II of the 13 paints (p=0.02). Reliability tvas better in c ontrols (intraclass correlation coefficients (ICC) ranging from 0.55 t o 0.85) than in headache patients (ICC ranging from 0.43 to 0.78). A m oderate negative association between PPT and pain intensity was demons trated. The intraindividual PM difference (PPT on the most painful occ asions-PPT on the least painful occasions) was negative at 12 of 13 ce phalic points (p=0.003, across-location mean difference: -0.20 kg/cm(2 )). The PPT differed significantly from one day to the next, A part of this variation tvas presumably related to the circumstances around th e procedure; thresholds were lower then the subjects came directly to algometry without any:preceding medical examination at all 13 points ( p=0.0002). These results have implications fe; the planning of future algometer studies. The sample size that is required in studies of head ache patients is greater than that in studies of healthy subjects, esp ecially when patients suffer from pain during the PPT session. Particu lar attention should be paid to circumstances (e.g. preceding medical investigations) around the algometry procedure in order to reduce vari ability.