Prem Bajaj

Osteoarthritis and its association with muscle hyperalgesia: an experimental controlled study.

&NA; Hypertonic saline effectively excites muscle nociceptors. Muscle hyperalgesia was assessed in osteoarthritis (OA) by intramuscular infusion of 0.5 ml hypertonic saline (6%) into the tibialis anterior muscle in humans. Patients (n=14) with OA in the lower extremities were compared with an equal number of age‐ and sex‐matched healthy controls. Ten of the 14 OA patients had pain in the knee joint as the most common presenting complaint. Visual analogue scale (VAS) pain intensity and assessment of pain areas were recorded before infusion and immediately, 2, 5, 10 and 20 min after infusion, and then every 10 min, until the pain vanished. The mean pain offset time in OA patients (11.3±7.9 min) was larger as compared with the control subjects (6.04±2.1 min) (P=0.025). OA patients had increased pain intensity VAS after the infusion in the right leg compared with controls (P<0.05). Referred and radiating pain areas at 2 min post‐infusion increased in OA patients and not in controls as compared with the local pain areas (P<0.05). It is concluded that muscle hyperalgesia and extended pain areas might be due to central sensitization caused by painful osteoarthritis.

Endometriosis Is Associated With Central Sensitization: A Psychophysical Controlled Study

Endometriosis is a pain syndrome representing a major cause of pelvic pain in women of reproductive age. The aim of this study was to test the hypothesis that persistent nociceptive input from endometriotic tissues leads to central sensitization manifested by somatic hyperalgesia and increased referred pain areas to experimental saline-induced muscle pain in patients with endometriosis, compared to healthy control subjects. Ten women with laparoscopically confirmed endometriosis and 10 healthy, age-matched women participated in the study. Hypertonic saline (0.5 mL, 5.8%) was injected intramuscularly, in random succession, into 1 site of menstrual pain referral (the multifidus muscle at the low back) and into 1 non-pain control site (first dorsal interosseous muscle [FDI] of the hand). The post-saline pain intensity and pain areas at the FDI were significantly greater in patients with endometriosis than in control subjects (P <.05) but were not different between the groups for the back. An absence of enhancement of post-saline pain responses at the back in the endometriosis group suggests that saline-induced pain at the back appears to activate segmental inhibitory systems in patients with endometriosis. Manifestation of central sensitization in women with endometriosis is demonstrated by increased muscle nociceptor input in the form of increased post-saline pain intensity, pain areas at the FDI, and hypersensitivity to pressure stimulation. These findings provide new insights into the complex pain mechanisms associated with endometriosis.

A comparison of modality-specific somatosensory changes during menstruation in dysmenorrheic and nondysmenorrheic women.

ObjectiveThe objective was to evaluate somatosensory thresholds to a multimodality stimulation regimen applied both within and outside areas of referred menstrual pain in dysmenorrheic women, over four phases of confirmed ovulatory cycles, and to compare them with thresholds in nondysmenorrheic women during menstruation. DesignTwenty dysmenorrheic women with menstrual pain scoring 5.45 ± 0.39 cm (mean ± standard error of mean) on a visual analog scale (10 cm) participated. Fifteen nondysmenorrheic women with a menstrual pain score of 0.4 ± 0.2 cm participated as controls. Ovulation was confirmed by an enzyme-multiplied immunoassay technique. Menstrual pain was described with the McGill Pain Questionnaire. Areas within menstrual pain referral were two abdominal sites and the midline of the low back, and the arm and thigh were the control areas. The pressure pain threshold (PPT) and pinch pain threshold were determined by a hand-held electronic pressure algometer, the heat pain threshold (HPT) by a contact thermode, and the tactile threshold with von Frey hairs. ResultsIn dysmenorrheic women the McGill Pain Questionnaire showed a larger sensory and affective component of pain than the evaluative and miscellaneous groups. The HPT and PPT were lower in the menstrual phase than in the ovulatory, luteal, and premenstrual phases, both within and outside areas of referred menstrual pain (p <0.01), with a more pronounced decrease at the referral pain areas. The pinch pain threshold was lower in the menstrual phase than in the ovulatory phase (p <0.02), and the tactile threshold did not differ significantly across the menstrual phases or within any site. Dysmenorrheic women had a lower HPT at the control sites and a lower PPT at the abdomen, back, and control sites, than in those of nondysmenorrheic women in the menstrual phase. ConclusionsThe results show reduced somatosensory pain thresholds during menstruation to heat and pressure stimulation, both within and outside areas of referred menstrual pain in dysmenorrheic women. Dysmenorrheic women showed a lower HPT at the control sites and a lower PPT at all the sites than those for nondysmenorrheic women in the menstrual phase. The altered somatosensory thresholds may be dependent on a spinal mechanism of central hyperexcitability, induced by recurrent moderate to severe menstrual pain.

Sensory changes during the ovulatory phase of the menstrual cycle in healthy women

This study compared the pain sensitivity in healthy women at the abdomen and lower back (presumed referral areas of menstrual pain), thigh and arm (control areas), in the menstrual, ovulatory, luteal and premenstrual phases of confirmed ovulatory cycles, with that of males. The pressure pain threshold (PPT) and pinch pain threshold (PiPT) was determined by an electronic pressure algometer, heat pain threshold (HPT) by a contact thermode and tactile threshold (TT) with von Frey hairs. The abdominal PPT was significantly lower in females in all menstrual phases as compared to the control sites ( p<0.0007). The abdominal and lower back HPT was significantly lower in females in all menstrual phases compared with control areas, and to the sites in males ( p<0.002). The TT was significantly reduced in females compared with males ( p< 0.013). There was no difference in the PiPT between females and males. In males, the HPT, PPT and TT were not different within any site. During the ovulatory phase, the HPT was significantly reduced at the abdomen and the PPT at the back compared with the menstrual, luteal and premenstrual phases (p<0.0002). There were no within‐menstrual phase variations in the PiPT and TT at any site, or for the HPT and PPT at the control areas. The reduced thresholds in menstruating women may be due to the presence of latent uterine algogenic stimuli, and the increased levels of oestrogen and leuteinizing hormone at ovulation may enhance nociception by acting both at the peripheral and central level, resulting in the hypersensitivity changes at the abdomen and lower back areas. Copyright 2001 European Federation of Chapters of the International Association for the Study of Pain Copyright 2001 European Federation of Chapters of the International As̋Ér the Study of Pain

Trigger Points in Patients with Lower Limb Osteoarthritis

Objectives: Studies have shown that osteoarthritis [OA] is associated with hyperalgesia and weakness in muscles resulting in muscle strain, poor positioning, and inappropriate muscle use. Hyperalgesia and indirect injuries resulting from forces generated within the musculoskeletal structures during activity may result in the formation of trigger points [TrPs]. The purpose of this study was to compare the occurrence of TrPs in healthy controls and patients with OA of the lower limbs. Methods: Both lower limbs of fourteen OA patients and an equal number of age and sex matched healthy controls were palpated for the presence of TrPs by examining the local twitch reaction, taut bands, nodules, and the pattern of pain radiation and pain referral. Results: Significantly greater numbers of latent TrPs in muscles acting on the hip joint were present in the OA patients with OA secondary to trauma [N = 9], as compared to the controls with out any history of trauma [N = 9] [P < 0.05]. In creased TrPs were found in muscles acting on the knee joint in knee OA as compared to hip OA [P = 0.016]. The total number of TrPs in OA patients correlated with the radiological scores of OA [Spearmans R = 0.57, P = 0.04]. The pain evoked by pressure to the TrPs in OA patients was associated with a significantly larger radiation and referral as compared to the control subjects [P < 0.05]. Conclusion: The large number of TrPs in secondary [traumatic] OA patients may be due to hyperalgesia resulting from the chronic nociceptive inputs from the sensitized joint nociceptors and central sensitization. The treatment or elimination of TrPs may play an important role in pain relief of chronic OA of lower limbs.

Muscle hyperalgesia in postexercise muscle soreness assessed by single and repetitive ultrasound stimuli

Abstract This study hypothesized the presence of muscle hyperalgesia and central hyper-excitability in postexercise muscle soreness (PEMS). PEMS was induced by standardized eccentric exercise of the first dorsal interosseous (FDI) muscle of the right hand using a newly designed hand exerciser. The left-hand FDI served as a control. Concentric maximum voluntary contraction, pressure pain threshold (PPT), pain threshold to a single ultrasonic stimulus (US1), and pain summation threshold to a 2 Hz train of five ultrasonic stimuli (US5) were used to assess the FDI. Measurements were performed at intervals up to 48 hours after exercise. The PPT in the test hand was minimum after 24 hours. US1 was not significantly different in the test and control hands at any time before or after the exercise, whereas US5 was significantly lower than control after 24 hours (P =.03). Facilitation of the temporal summation pain threshold, calculated as a ratio between US1 and US5, was maximum at 24 hours compared with the control hand (P =.005). This indicates that temporal summation was facilitated as a component of the muscle hyperalgesia and the ultrasonic stimuli can be used as a noninvasive method to determine central mechanisms of muscle hyperalgeisa.

Facilitation and inhibition of withdrawal reflexes following repetitive stimulation: electro- and psychophysiological evidence for activation of noxious inhibitory controls in humans

A systematic evaluation of nociceptive withdrawal reflexes and pain rating was undertaken in order to explore the mechanisms underlying temporal summation of repetitive electrocutaneous stimulation in healthy individuals (n=12; age=27.5 ± 1.5 years). Five‐second subreflex threshold (RT) electrocutaneous stimulation at different frequencies (single stimulus, 5, 10, and 20 Hz) and intensities (0.6RT and 0.8RT) was applied on the dorsum of the foot, and the withdrawal reflex from the ipsilateral biceps femoris muscle was measured. The subjects scored the pain intensity on a visual analogue scale (0–100 mm) for the beginning, the middle and the end phase of the 5 s series of stimulation, and the respective averaged reflex size was calculated. The reflex size increased at stimulus frequencies 10 Hz × 0.8RT and 20 Hz × 0.8RT as compared with 5 Hz × 0.8RT (SNK, P<0.05), and by an increase in current intensity from 0.6RT to 0.8RT (SNK, P<0.05). Pain intensity increased with the increase in the current intensity from 0.6RT to 0.8RT (SNK, P<0.05). Profound activation of inhibition following electrocutaneous pain stimuli was demonstrated by reduction in pain intensity and reflex size during the last second as compared with the first second at 0.6RT current intensity (SNK, P<0.05). The pain intensity peaked between 5 and 10 Hz (P<0.05) and was reduced at 20 Hz for current intensities at 0.8RT (P<0.05). This study provides evidence for both frequency dependent central integration of the repetitive electrocutaneous stimuli and activation of a pain inhibitory system by psychophysical and electrophysiological means, demonstrating the delicate balance between neuronal facilitation and inhibition in the human pain system.

Prophylactic tolperisone for post‐exercise muscle soreness causes reduced isometric force—adouble‐blind randomized crossover control study

The role of tolperisone hydrochloride, a centrally acting muscle relaxant in relieving painful muscle spasm is recently being discussed. The present study hypothesizes that the prophylactic use of tolperisone hydrochloride may effectively relieve post‐exercise muscle soreness, based on the spasm theory of exercise pain. Twenty male volunteers, aged 25.2±0.82 years (mean±SEM) participated in 10 sessions in which they received oral treatment with placebo or the centrally acting muscle relaxant tolperisone hydrochloride (150 mg) three times daily for 8 days, in randomized crossover double‐blind design. Time course assessments were made for pressure pain threshold, Likerts pain score (0–5), pain areas, range of abduction, isometric force, and electromyography (EMG) root mean square (RMS) during maximum voluntary isometric force on day 1 and 6, immediately after an eccentric exercise of first dorsal interosseous muscle, and 24 and 48 h after the exercise. Treatment with placebo or tolperisone hydrochloride was initiated immediately after the assessments on the first day baseline assessments. On the sixth day baseline investigations were repeated and then the subjects performed six bouts of standardized intense eccentric exercise of first dorsal interosseous muscle for provocation of post‐exercise muscle soreness (PEMS). Perceived intensity of warmth, tiredness, soreness and pain during the exercise bouts were recorded on a 10 cm visual analogue pain scale. VAS scores and pressure pain thresholds did not differ between tolperisone and placebo treatment. All VAS scores increased during the exercise bouts 2, 3, 4, 5 and 6 as compared to bout 1. Increased pain scores and pain areas were reported immediately after, 24 and 48 h after exercise. Pressure pain thresholds were reduced at 24 and 48 h after the exercise in the exercised hand. Range of abduction of the index finger was reduced immediately after the exercise and was still reduced at 24 h as compared to the non‐exercised hand. The EMG RMS amplitude was also reduced immediately after the exercise, but was increased at 24 and 48 h. Isometric force was reduced immediately after the exercise as compared to days 1, 6, and the 24 and 48 h post‐exercise assessments with a greater reduction following the tolperisone hydrochloride treatment and the reduction was more in tolperisone group as compared to the placebo group. The results suggest, that the prophylactic intake of tolperisone hydrochloride provides no relief to pain in course of post‐exercise muscle soreness but results in reduction in isometric force.