Measurement of pain threshold in patients with rheumatoid arthritis, osteoarthritis, ankylosing spondylitis, and healthy controls.

Pain threshold was measured using a pressure algometer in 126 subjects, of whom 54 were females and 72 males. These subjects included 18 males and 18 females with rheumatoid arthritis, 18 males and 18 females with osteoarthritis, 18 males with ankylosing spondylitis, and 18 male and 18 female healthy control volunteers. Six points were studied on each side of the body: 2 cm above the eyebrow on the forehead, lateral aspect of the arm at the insertion of the deltoid muscle, midpoint of the ulna, hypothenar eminence in the palm, midpoint of the quadriceps muscle, and midpoint of the antero-medial aspect of the tibia. None of these points corresponded to the "trigger" points in fibromyalgia. The pain threshold was statistically significantly higher in patients with ankylosing spondylitis than in patients with osteoarthritis, and these in turn were statistically higher than in the normal subjects. Patients with rheumatoid arthritis had significantly lower pain thresholds than the normal subjects. No laterality in pain threshold was identified, but females had in general a lower pain threshold.