Discordant Relationship Between Evaluation of Facial Expression and Subjective Pain Rating Due to the Low Pain Magnitude.

INTRODUCTION: Facial expression to pain is an important pain indicator; however, facial movements look unresponsive when perceiving mild pain. The present study investigates whether pain magnitude modulates the relationship between subjective pain rating and an observer's evaluation of facial expression. METHODS: Twelve healthy volunteers were recruited to obtain 108 samples for pain rating with Visual Analogue Scale (VAS). Subjects underwent three different mechanical painful stimuli (monofilament forces of 100 g, 300 g, and 600 g) over three sessions and their facial expressions were videotaped throughout all sessions. Three observers independently evaluated facial expression of the subjects with a four-point categorical scale (no pain, mild pain, moderate pain, and severe pain). The correlations between subjective pain ratings and the evaluation of facial expression were analyzed in dichotomous group which was low pain ratings (VAS<30), or high pain rating (VAS≥30). RESULTS: Subjective pain ratings was significantly correlated with the evaluation of facial expression in high pain ratings, however no correlation was found between them in mild pain ratings. In mild pain ratings, most of the subjects (78%) were rated as no pain by observers, despite the fact that subjects reported pain. CONCLUSION: The results suggest that the evaluation of facial expression of pain was difficult for the observer to detect pain severity when the subjects feel mild pain.

Relationship between biological factors and catastrophizing and clinical outcomes for female patients with knee osteoarthritis.

AIM: To investigate the correlations between clinical outcomes and biopsychological variables in female patients with knee osteoarthritis (OA). METHODS: Seventy-seven patients with symptomatic knee OA were enrolled in this study. We investigated the age, body mass index (BMI), pain catastrophizing scale (PCS) and radiographic severity of bilateral knees using a Kellgren-Lawrence (K-L) grading system of the subjects. Subsequently, a multiple linear regression was conducted to determine which variables best correlated with main outcomes of knee OA, which were pain severity, moving capacity by measuring timed-up-and-go test and Japanese Knee Osteoarthritis Measure (JKOM). RESULTS: We found that the significant contributor to pain severity was PCS (ß = 0.555) and BMI (ß = 0.239), to moving capacity was K-L grade (ß = 0.520) and to PCS (ß = 0.313), and to a JKOM score was PCS (ß = 0.485) and K-L grade (ß = 0.421), respectively. CONCLUSION: The results suggest that pain catastrophizing as well as biological factors were associated with clinical outcomes in female patients with knee OA, irrespective of radiographic severity.

Unilateral hindpaw inflammation induces bilateral activation of the locus coeruleus and the nucleus subcoeruleus in the rat.

Several lines of evidence have shown that unilateral hindpaw inflammation produces activation of the locus coeruleus (LC) and the nucleus subcoeruleus (SC), resulting in descending modulation of nociceptive processing in the dorsal horn. However, it is unclear if the LC/SC is activated unilaterally or bilaterally following the development of unilateral hindpaw inflammation. The present study was designed to clarify this question. For the induction of unilateral hindpaw inflammation, lambda carrageenan (2.0mg in 0.15ml saline) was injected subcutaneously into the plantar surface of the left hindpaw. Four hours after carrageenan injection, in the LC/SC both ipsilateral and contralateral to the inflamed paw, the number of Fos-positive cells increased significantly in carrageenan-injected rats when compared to vehicle (saline)-injected and untreated control rats. The Fos expression in the LC/SC was equivalent bilaterally in the carrageenan-injected rats, as well as in vehicle-injected and untreated control rats. For nociceptive testing, the paw withdrawal latency, which measures cutaneous hyperalgesia in response to thermal stimuli, was determined in rats receiving a unilateral lesion of the LC/SC either ipsilateral or contralateral to the inflamed paw. Two and a half hours after the induction of inflammation, in both groups of rats with unilateral lesion, paw withdrawal latencies decreased significantly in the LC/SC-lesioned rats. However, there was no significant difference in paw withdrawal latencies between the LC/SC-lesioned rats and sham-operated rats, indicating that unilateral activation of the LC/SC is sufficient for modulating nociceptive processing in the dorsal horn. These results suggest that unilateral hindpaw inflammation induces bilateral activation of the LC/SC.