How does previous corticosteroid treatment affect the biopsy findings in giant cell (temporal) arteritis?

Objective: To determine the effect of previous corticosteroid treatment on the results of temporal artery biopsy. Design: Consecutive case series. Setting: Tertiary care center. Patients: A consecutive cohort of 535 patients who had temporal artery biopsies at Mayo Clinic, Rochester, Minnesota, between 1 January 1988 and 31 December 1991. Measurements and Results: The dose and duration of corticosteroid treatment received before temporal artery biopsy and detailed clinical and laboratory data were obtained from the patients' medical records. All temporal artery biopsy slides were re- evaluated by a pathologist blinded to clinical data, previous corticosteroid treatment information, and the original pathologic diagnosis. Biopsy specimens were classified as negative for arteritis, positive for typical temporal arteritis, or positive for atypical temporal arteritis. Biopsy results were positive for 31% of patients (89 of 286) who did not receive corticosteroids before biopsy and for 35% of those (86 of 249) who did receive corticosteroids before biopsy (P = 0.4; 95% confidence interval for the difference, -4.7% to 11.5%). Patients who received corticosteroids before biopsy tended to have clinical features more suggestive of arteritis. A multiple logistic regression analysis model, controlling for these differences in clinical and laboratory features, showed that the biopsy positivity rate was unrelated to previous corticosteroid treatment. Conclusions: Although these results do not prove that histologic features are unaffected by corticosteroids, they show that, in this large, consecutive sample, the positivity rates of temporal artery biopsy were similar in untreated and corticosteroid-treated patients. Temporal artery biopsy may show arteritis even after more than 14 days of corticosteroid therapy in the presence of clinical indications of active disease.