Mechanical sensation and pain thresholds in patients with chronic arthropathies.

This study measured mechanical sensation and pain thresholds in the cutaneous field overlying the knee joints of rheumatoid arthritis (RA; N = 27) and osteoarthritis (OA; N = 28) patients, compared with age- and weight-matched normal control subjects (Norm; N = 27) by using graded von Frey monofilaments. A visual analog scale (VASpain), cutaneous joint temperature and circumference were measured for subjective ongoing pain and inflammation. Compared to Norm, RA and OA groups had (1) significantly higher VASpain scores, joint circumferences and (RA only) surface temperatures, (2) significantly increased average thresholds for innocuous mechanical sensation (0.014 +/- 0.003 vs 0.077 +/- 0.035 and 0.123 +/- 0.043 g, respectively) indicative of hypoesthesia and (3) significantly decreased pain thresholds, indicative of mechanical allodynia (446.683 +/- 0 vs 285.910 +/- 40.012 and 322.681 +/- 34.521 g for Norm vs RA and OA, respectively). Intrapatient joint temperature, circumference, and pain threshold were significantly correlated in RA. The highest scores in average mechanical sensation mapped to the same grid region as the lowest scores in average pain thresholds in RA and OA patients. The simultaneous hypoesthesia and allodynia, with paradoxical decrease in sensation and increased pain thresholds may reflect peripheral and central alterations in neuronal responsiveness to mechanical stimulation and suggests activation of a descending inhibitory system.