MODULATION OF PRESSURE PAIN THRESHOLDS DURING AND FOLLOWING ISOMETRICCONTRACTION IN PATIENTS WITH FIBROMYALGIA AND IN HEALTHY CONTROLS

This study aimed at evaluating the influence of submaximal isometric c ontraction on pressure pain thresholds (PPTs) in 14 fibromyalgia (FM) patients and 14 healthy volunteers, before and after skin hypoesthesia . PPTs were determined with pressure algometry over m. quadriceps femo ris before, during and following an isometric contraction. Maximum vol untary contraction (MVC) was assessed using a computerized dynamometer . A contraction of 22% MVC on average was held until exhaustion (max. 5 min) and PPTs were assessed every 30 sec. A local anesthetic cream a nd a control cream were applied following a double-blind design and PP Ts were reassessed. In healthy volunteers PPTs increased during contra ction (P < 0.001), then decreased after the end of contraction (P < 0. 001) but remained above precontraction values during the 5 min of post -contraction assessments (P < 0.001). In FM patients PPTs decreased in the middle of the contraction period (P < 0.05) and remained below pr econtraction levels during the rest of the contraction period (P < 0.0 5) and during the 5 min of post-contraction assessment (immediately po st-contraction NS; 2.5 min post-contraction P < 0.01; 5 min post-contr action P < 0.05). The normalized PPTs were significantly lower in pati ents than in controls during contraction (start P < 0.01; middle P < 0 .001; end P < 0.001) and at all times during post-contraction assessme nts (P < 0.001). Anesthetic cream raised PPTs at rest in controls (P < 0.01) but not in FM patients, and did not influence contraction or po st-contraction PPTs in either group. Therefore, the increased pressure pain sensibility in FM patients is more pronounced deep to the skin. The observed decrease of PPTs during isometric contraction in FM patie nts could be due to sensitization of mechanonociceptors caused by musc le ischemia and/or dysfunction in pain modulation during muscle contra ction.