The role of excess subcutaneous fat in pain and sensory sensitivity in obesity

Background Previous studies suggest pain sensitivity may be decreased in obesity, but it is unknown whether this is a global or a site-specific phenomenon related to the amount of excess fat. Methods Design: a cross-sectional study comparing obese and non-obese participants on body sites with much and little excess subcutaneous fat in obesity. Hot and cold sensory detection thresholds, pain thresholds, pain tolerance and subjective ratings for a cold (0 degrees C) and hot (48 degrees C) stimulus were assessed using a 16x16mm thermode (Medoc, Israel) on the forehead and abdomen. Pressure pain thresholds were measured on the hand. Cold water immersion tolerance duration and subjective ratings were assessed on the hand. Two indices of central pain processing, i.e., temporal summation and heterotopic noxious stimulation, were assessed. Results A total of 20 obese participants [10M/10F, BMI mean (SD)=41.5kg/m(2) (9.4kg/m(2))] and 20 age- and gender-matched non-obese controls [10M/10F, BMI mean (SD)=23.5kg/m(2) (2.9kg/m(2))] were studied. Compared with non-obese, obese participants had higher thresholds and lower subjective ratings, indexing decreased sensitivity, for painful and non-painful thermal stimuli on the abdomen, an area with much excess subcutaneous fat. Decreases in abdominal sensitivity correlated with measures of adiposity (i.e., waist-to-hip ratio and subcutaneous fat thickness). On areas with little excess subcutaneous fat (forehead and hand), obese and non-obese groups did not differ in measures of thermal or pressure sensitivity, nor for indices of central pain processing. Conclusion Obese participants are less sensitive than non-obese individuals, but only on areas with excess subcutaneous fat.