Giant Cell Arteritis and Takayasu Arteritis: Are They Similar or Different?

Vasculitis is a group of heterogeneous conditions characterised by inflammation of blood vessels. Based on the predominant size of the affected vessel, vasculitis is classified into small, medium, and large vessel vasculitis (LVV). Giant cell arteritis (GCA) and Takayasu's arteritis (TAK) are the two major types of LVV. GCA was thought to affect only the external carotid artery and its branches, whereas, TAK was thought to affect the aorta and its major branches. Advances in imaging techniques have led to a better understanding of these conditions. It has become increasingly clear that GCA can involve the aorta and its branches. GCA and TAK have overlapping features like propensity to affect the aorta and its branches, similar histopathology, and similar clinical features. However, there are differences in age, geographic location, genetics, and predominant vascular territory involvement. There are subtle differences in clinical features. Are these conditions different ends of the same spectrum or different conditions with similar features? This review compares and contrasts these two conditions based on epidemiology, genetics, pathology, predominant vascular territory involvement, and any differential response to treatment. Based on current evidence, GCA and TAK seem to be distinct conditions and not different ends of the same spectrum.