Background/Purpose: Temporal artery biopsy (TAB) showing transmural inflammation is considered the gold standard for the diagnosis of giant cell arteritis (GCA). In some cases, inflammation is confined to the periadventitial small vessels and/or to the adventitia. The aim of the present study was to compare treatment and long-term outcomes of patients with transmural inflammation with those of patients with periadventitial and/or adventitial inflammation in a single center cohort of patients with biopsy-positive GCA with long term follow-up.

Methods: All TABs performed for suspected GCA between 1986 and 2013 were reviewed by a single pathologist. Based on the localization of the inflammation, inflamed TABs were classified into 2 categories: transmural inflammation (TMI), with external elastic lamina disruption and extension of the inflammation to the media; periadventitial and/or adventitial inflammation (PA/AI), with inflammation limited to small periadventitial vessels devoid of muscular coat and/or to the adventitia without extension to the media. All medical records of these patients were retrospectively reviewed from the date of TAB to 31 December 2018 or death. Only patients with a follow-up duration of at least 18 months after GCA diagnosis were included.

Results: In the study period, 274 TMI and 80 PA/AI were identified. Baseline clinical manifestations and laboratory findings of the two study cohorts have been already reported (1). Large vessel involvement was found in 6/22 (27%) patients with PA/AI and 32/81 (40%) patients with TMI, p=0.292. 118 patients with TMI and 35 with PA/AI had a follow-up duration longer than 18 months and were included for the outcomes analysis. Median (IQR) follow-up duration was 79.5 months (52, 114) for patients with TMI and 67 months (34, 124) for those with PA/AI, p=0.125. Compared to patients with TMI, those with PA/AI received a significant lower initial prednisone dose (mean (SD) 35.8 mg (22.0) vs 46.8 (15.0), p< 0.0001), reached sooner a prednisone dose < 10 mg/day (median 20 weeks vs 26, p=0.004) and < 5 mg/day (median 32 weeks vs 44, p=0.005), had a lower cumulative prednisone dose at 1 year (mean (SD) 5.8 gr (3.8) vs 7.2 (2.3), p=0.005) and at the end of the follow-up period (mean (SD) 10.0 gr (9.0) vs 12.9 (9.6), p=0.015), and showed a trend for an earlier first relapse (median 52 weeks vs 63, p=0.052). There were no differences in the frequencies of relapse (43% of patients with TMI vs 46% of those with PA/AI, p=0.794) and long term remission (53% of patients with TMI vs 49% of those with PA/AI, p=0.616), time to first GC discontinuation (median 72 weeks in patients with TMI vs 62 weeks in those with PA/AI, p=0.080) and treatment duration (median 33.5 months in patients with TMI vs 26 months in those with PA/AI, p=0.159).

Conclusion: Our study demonstrates for the first time that patients with GCA with isolated periadventitial and/or adventitial inflammation and those with the classic transmural pattern have similar frequency of large vessel involvement and similar disease course. These data confirm that TAB showing inflammation confined to the periadventitial small vessels and/or the adventitia could be considered part of the histopathologic spectrum of GCA.
1. Am J Surg Pathol. 2014;38:1360-70

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/comparison-between-transmural-and-isolated-periadventitial-and-or-adventitial-inflammation-at-temporal-artery-biopsy-a-single-center-cohort-of-biopsy-positive-gca-with-long-term-follow-up/