Countless vascular and immunologic disorders are linked to aberrant Rho-associated protein kinase (ROCK) activity. Previously, researchers found that patients with clinical giant cell arteritis (GCA) have higher ROCK activity in histopathologically negative temporal artery biopsies (TABs) than patients without GCA. The objective of the present study was to confirm the earlier findings and assess ROCK activity in a larger cohort of GCA patients who had negative biopsies.

Subjects were divided into 2 groups based on clinical data collected 6 months after TAB: those with biopsy-negative GCA and controls without GCA. Two pathologists who were blind to the clinical diagnosis stained paraffin-embedded TABs for phosphorylated ezrin/radixin/moesin (pERM), a surrogate for ROCK activity, and assessed the staining intensity in 3 different locations of the vasculature.

About 43 controls and 36 patients with biopsy-negative GCA were examined. In patients without GCA, the mean (SD) pERM intensity score was 3.9 (1.4), as opposed to 5.0 (1.4) in subjects with GCA (P=0.002). Participants with GCA were substantially more likely than non-GCA subjects to have a high pERM intensity score using the specified cut-off of 4 (odds ratio 3.67, 95% CI 1.19-11.36; P=0.02). A high pERM intensity score had an 86% sensitivity for identifying GCA in histologically negative TABs (95% CI 70-95).

In the cohort, those with biopsy-negative GCA scored considerably higher on the pERM intensity scale than those without GCA. In addition to improving TAB’s sensitivity, pERM staining has diagnostic value in that it can assist in identifying the clinically significant subset of biopsy-negative GCA.