Polymyalgia rheumatica. Assessment of disease activity using erythrocyte sedimentation rate and plasma viscosity.

Comparison of clinically assessed activity of disease with 112 paired readings of the erythrocyte sedimentation rate (ESR) and the plasma viscosity (PV) in 23 patients with polymyalgia rheumatica (PMR) showed the following. (1) A correlation between ESR and PV in both sexes, reaching the significance obtained in a comparison group of patients with rheumatoid arthritis (RA) (109 paired readings), with no significant difference between the PMR and RA groups on analysis of variance of the regression slopes. (2) A degree of scatter of readings around the regression lines so that they could not be used for prediction of ESR from the PV or vice versa. (3) varkappa(2) analysis of normal and abnormal values of ESR and PV which showed a highly significant correlation. However 10 readings were abnormally high for ESR in the presence of a normal PV. 5 of these 10 observations were associated with clinical features of disease activity. 20 readings were abnormally high for PV in spite of a normal ESR with only one instance of clinical activity. These data indicate that it is not possible to provide exact guidelines for a ;safe' level of ESR or PV applicable to the individual patient, and measurement of both these indices of disease activity is recommended.