Serum lactic dehydrogenase as a marker of joint damage in rheumatoid arthritis.

SIR, There are important differences between the study of Ishigami et al and our report' which may explain the apparently discordant findings. Ishigami's study included 58 patients treated with gold over a 12 month period. Although we are not told, one assumes that the gold preparation and the dose schedule used were similar in both studies. In Ishigami's study gold therapy was 'considered successful in controlling or reducing disease activity by both clinical and laboratory criteria'. The only data offered in support of this claim, however, are changes in erythrocyte sedimentation rate (ESR) (Westergren?) and peripheral blood haemoglobin levels. If the pretherapy ESR values in the two studies are compared (mean (SD): 48 (27) Ishigami et al; 59 (25) Hanly and Bresnihan) it would appear that the latter group of patients had more active disease. Furthermore, the six month post-therapy ESR in our study (mean (SD): 24 (11)) compared with the 12 month post-therapy value in the study of Ishigami et al (mean (SD): 32 (21)) indicates a greater reduction in disease activity in the former group. This may be important as, in our study, the greatest fall in peripheral blood lymphocytes occurred with the initial and most marked reduction in disease activity. Therefore, such a change may not be apparent in patients whose pretherapy disease activity is less marked and who have a less dramatic reduction in disease activity with gold therapy. As Ishigami's study is a retrospective review, presumably detailed assessments of articular disease activity were not available on all patients. Such data are essential to allow accurate measurement of the response to therapy. Some patients clearly had a fall in lymphocyte counts while receiving gold therapy and one wonders if these patients also had the greatest reduction in disease activity. We have seen our initial findings reproduced in additional patients currently entered in a prospective study of gold therapy in rheumatoid arthritis (unpublished observations, Rooney and Bresnihan). Total circulating lymphocyte counts, however, may be too insensitive to detect changes in all such patients. As Ishigami et al point out the absence of a fall in the total lymphocyte count does not preclude changes in lymphocyte subpopulations and lymphocyte function, as recently reported by Hassan et al.)