• polymyalgia rheumatica
• autoinflammatory disease
• autoimmunity.

Polymyalgia rheumatica (PMR) is an elderly onset syndrome characterised by aching and stiffness in the shoulders and the pelvic girdle associated to increased levels of acute phase reactants and rapid response to glucocorticoids.1 Although the cause of PMR remains unknown, most of the evidence suggest a multifactorial aetiology inducing an immunomediated pathogenesis.1 2

According to the ‘immunological continuum model’ proposed by McGonagle in 2006, all immune-mediated diseases can be conceptualised as predominantly autoinflammatory, predominantly autoimmune or mixed, on the basis of the relative contributions of innate and adaptive immune responses.3 Autoinflammatory diseases (AIDs) are characterised by tissue inflammation mainly due to aberrant activation of innate immune system without autoantibodies production and autoreactive T lymphocyte activation. In contrast, autoimmune diseases (ADs) are typically depicted by an abnormal activation of the adaptive immune system.4 However, the emerging understanding of the close linkage between innate and adaptive immunity led to consider the rare monogenic AIDs and ADs as the two opposite ends into a continuum of immune-mediated disorders, where middle entities are recognised (figure 1).3

In the view of this background, we tried to envisage the most suitable place for PMR into the spectrum of the autoinflammatory/autoimmune disorders by reviewing and interpreting current evidence.

Clear indication for a prevalent autoinflammatory background of PMR is related to the disease onset and course. Actually, starting of symptoms is generally over a few days or overnight in PMR,1 as well as in inflammatory periodic-recurring occurrence of AIDs,5 but in contrast to classic polygenic ADs where a subacute onset is frequently recorded (figure 2A).6 Further, after low-dose glucocorticoid therapy initiation, patients with PMR experience a rapid improvement of symptoms, generally within 24–72 hours, and more than 40% of them achieve …