Experimental Arthritis

The ability to determine the severity of joint disease by gross physical examination is a useful clinical feature, because a numerical score is reflective of the degree of inflammation. The standard method reported in the literature assigns numerical values to digits and paws of each of the four limbs, with 0 = no signs, 1 = swelling or redness in one digit, 2 = swelling or redness in two or more digits, and 3 = swelling or redness in the entire paw. The scores from each of the four limbs are then added to obtain an arthritic score. Observations in T cell receptor transgenic mice, which develop an acute onset of collagen-induced joint disease,40 suggested that when an entire paw was red or swollen, it was painful to the mouse. On the other hand, mice showed no apparent discomfort when joint disease was restricted to individual digits. Therefore, the discrepancy in correlation between arthritic score and distress became evident when comparing disease severity. For example, if a single digit on each of three limbs was affected, the mouse showed very little discomfort but had an arthritic score of 3. A mouse with an entire paw affected but on only one limb still had an arthritic score of 3 but was in obvious distress. Therefore, the scoring method was altered by multiplying each individual limb score by itself, thereby magnifying the scores associated with entire paw involvement, and then adding these multiplication grading scores from each limb to obtain a modified arthritic score.

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