Distinct Histological Patterns of GCA Described

Researchers have distinguished 4 histological patterns in patients with giant-cell arteritis (GCA), an inflammatory blood vessel disease that most often affects medium and large arteries in the scalp and head. The findings were published in the the journal Medicine.

Approximately 50% of patients with GCA have overlapping symptoms of polymyalgia rheumatica (PMR), and an estimated 5-15% of patients with PMR are diagnosed with GCA.² Patients with GCA tend to have the same demographics as patients with PMR: it only affects adults, who are typically older than 50 years, and it more commonly affects women compared with men and whites compared with non-whites.

According to the authors of the current study, previous research shows that “temporal arteries from GCA patients may exhibit a variable extent of inflammatory involvement, ranging from slight adventitial infiltrates to fully developed granulomatous lesions distributed along the entire vessel wall.” A variety of terms have been used to describe histological patterns of inflammation in GCA, and findings regarding the relationship between these patterns and clinical features have been mixed.

In addition to clarifying this relationship, the researchers sought to “describe and validate the main histological patterns found in GCA-involved temporal arteries, [and] to examine additional histological features, including the coexistence of different patterns in the same artery that assist in delineating a model of infiltration across the artery wall.”

The researchers recorded clinical and laboratory variables and performed histological examination of temporal artery biopsies (TAB) from 285 patients (200 female and 85 male) who fulfilled GCA classification criteria according to the American College of Rheumatology.

They identified 4 distinct histological inflammatory patterns: (1) adventitial pattern (n = 16 biopsies), in which inflammatory infiltrates were limited to the adventitia; (2) adventitial invasive pattern, characterized by adventitial involvement with some degree of invasion of the muscular layer (n = 21 biopsies); (3) concentric bilayer pattern, characterized by infiltration of the adventitia and intima with media layer preservation (n = 52 biopsies); and (4) panarteritic pattern, with distribution of inflammatory infiltrates through the 3 arterial layers (n = 196 biopsies).

Additionally, the researchers also observed coexisting patterns in 43% of TAB, and found a strong correlation between extensive artery inflammation and severe intimal hyperplasia.

While no statistically significant correlation between histological patterns and clinical or laboratory findings was observed, patients with a panarteric pattern more frequently had temporal artery abnormalities, jaw claudication, and scalp tenderness than patients with other patterns.

The authors noted that these findings further show that “glucorticoid therapy at full doses, at least during the first month, do not seem to influence the morphology and extent of the inflammatory infiltrates.” However, biopsies from patients treated with high doses for more than 1 month were not included in the study, so it is unknown whether such treatment would affect morphology. 

Clinical Summary and Applicability

Based on the 4 patterns observed in giant cell arteritis, researchers propose a dynamic model of the sequential invasion of the artery, likely reflecting steps in the progression of inflammation.The validation and description of these patterns “may be useful to standardize stratification of histological severity for immunopathology biomarker studies or correlation with imaging,” they concluded.

References

1. Hernández-Rodríguez J, Murgia G, Villar I, et al. Description and Validation of Histological Patterns and Proposal of a Dynamic Model of Inflammatory Infiltration in Giant-cell Arteritis. Medicine (Baltimore). 2016; 95(8):e2368.

2. Docken W on behalf of the American College of Rheumatology Committee on Communications and Marketing –Giant Cell Arteritis. Last updated online August 2013.  Accessed March 22, 2016. Source Code.