Polymyalgia rheumatica and giant cell arteritis: lumping versus splitting

The International Classification of Diseases considers polymyalgia rheumatica (PMR) and giant cell arteritis (GCA) as distinct disease entities.PMR is characterised by inflammation of musculoskeletal structures (tendons, ligaments, joint capsules) whereas GCA is a vasculitis of large and medium sized blood vessels.Incidence patterns are similar, and they are often co-diagnosed, either concurrently or at different times(1).Shared pathophysiological mechanisms have been proposed but the causes remain unclear.Vascular imaging studies suggest that some patients with PMR have imaging features of GCA(2).This apparent blurring of disease boundaries has potential implications for patient care in diseases where treatment guidelines appear to provide little flexibility for the individual.GCA is