Plasma viscosity in giant cell arteritis as a predictor of disease activity.

Thirty one patients with giant cell arteritis (GCA) receiving standardised prednisolone treatment were followed up for one year with analyses of plasma viscosity, erythrocyte sedimentation rate (ESR), C reactive protein (CRP), and fibrinogen concentration. On the day of diagnosis all patients had an increased plasma viscosity and ESR, whereas the concentration of CRP was normal in three patients and fibrinogen concentration and haptoglobin values were normal in one patient. IgG levels were increased in two patients. Plasma viscosity correlated significantly with the ESR, IgG level, and fibrinogen concentration. Laboratory variables in subgroups of patients with GCA proved by biopsy were not different from the whole group of patients with GCA. The follow up showed that CRP normalised faster than the ESR, plasma viscosity, and fibrinogen concentration. Plasma viscosity and the ESR paralleled clinical findings more closely and predicted flare ups better than the other variables. Plasma viscosity had advantages over the ESR for predicting flare ups and in the clinical monitoring of treatment with glucocorticoids.