Polymyalgia rheumatica (PMR) is an inflammatory rheumatic disease characterised by pain and stiffness of neck, shoulder- and hipgirdle, typically with elevated acute phase reactants (APR). However, patients may present with normal APR. Our aim was to explore whether normal APR were due to 1) 'caught early in the disease', 2) misdiagnosis, or 3) a distinct subset of PMR with different clinical presentation and prognosis.
This was a retrospective cohort study on patients with clinical PMR diagnosis visiting the rheumatologists of the Sint Maartenskliniek from April 2008 to September 2017.
Of 454 patients, 62 patients had normal, and 392 elevated APR. Normal APR patients had longer symptom duration before diagnosis (13 vs. 10 weeks; p=0.02), however, during follow-up 31% developed elevated APR. In elevated APR patients with previous APR data available while already symptomatic, 58% had earlier normal APR. Fewer normal APR patients had peripheral arthritis (2% vs. 9%;p=0.04), and anaemia (17% vs. 43%; p=0.001). More often they had a previous PMR diagnosis (16% vs. 8%; p=0.057) and a shorter median time to glucocorticoid-free remission (552 vs. 693 days; n=36 vs. 160; p=0.02). Route of GC administration differed between groups (p=0.026). Fewer patients received methotrexate; 3 vs. 12%; p=0.046). No difference in alternative diagnosis was observed.
PMR patients with long-term normal APR seem to be a milder subset of PMR in clinical presentation and prognosis. Additionally, our data also suggest there is a subgroup with normal APR who are caught early in the disease. Misdiagnosis does not appear to play a role.