Polymyalgia rheumatica vs late-onset rheumatoid arthritis.

Polymyalgia rheumatica (PMR) is a well-defined acute musculoskeletal inflammation of ageing people and characterized by clinical symptoms that may create some difficulties in the differential diagnosis with late (elderly) onset RA (LO-RA or EO-RA, respectively) as well as with LO-RA with PMR-like onset (LO-RA/PMR) [1]. PMR as an inflammatory condition of multifactorial aetiology is generally characterized at least at the beginning by aching and stiffness in the shoulder and in the pelvic girdles. It occurs in people over the age of 50–60 yrs, and it usually responds rapidly to low doses of glucocorticoids and has a favourable prognosis. Genetic causes and polymorphisms of additional genes involved in the initiation and regulation of inflammatory reaction have been considered to be possible susceptibility factors for PMR [2]. In particular, TNF, and IL-1 receptor antagonist (IL-1Ra) gene polymorphisms are predisposing factors and may be implicated in the pathogenesis of PMR [3]. On the other hand, increased production of IL-6 is a characteristic finding in patients with PMR, and glucocorticoids rapidly reduce serum levels of IL-6 [4]. The suppression of the hypothalamic–pituitary–adrenal (HPA) axis as consequence of chronic stress and/or the endocrinosenescence could contribute to the pathogenesis of PMR [5]. Recently, a reduced production of adrenal hormones, like cortisol (CO) and DHEAS, has been shown in untreated PMR patients with active disease, as well as an increased 17-hydroxyprogesterone (PRG) production following adrenocorticotrophic hormone (ACTH) testing [6]. The occurrence of peripheral arthritis, particularly in both hands, may create some difficulties in the differential diagnosis between PMR and LO-RA. Symmetrical peripheral involvement, RF seropositivity, development of joint erosions and extraarticular manifestations differentiate adult RA from PMR. Anticitrullinated peptide (CCP) antibodies may also be useful in the differential diagnosis between PMR and LO-RA. However, several patients with seronegative LO-RA show a relatively mild symmetric synovitis, characterized by a rapid and complete response to glucocorticoid and a non-erosive course. Symptoms and signs of both PMR and LO-RA might alternate during the follow-up of the patients [7]. These patients show a clinical condition different from classic RA, which more closely resembles PMR, moreover at the beginning of the disease. On the other hand, a prospective study on clinical features of PMR and LO-RA with PMR-like onset showed that 20% of PMR patients developed overt RA during the follow-up period [8].