Polymyalgia rheumatica preceding small-vessel vasculitis: changed spots or misdiagnosis?

Systemic small-vessel vasculitis (SVV) is increasing in incidence and age of diagnosis. Presenting features may mimic those of polymyalgia rheumatica (PMR), a common disease of the elderly.

To test the hypotheses that SVV is frequently misdiagnosed as PMR in elderly patients, that this results in a delay in diagnosis and appropriate treatment, and that the natural history and clinical features are different.

Retrospective case-control study.

Cases of glomerulonephritis due to SVV at a single centre over a 12-year period were analysed, comparing those treated previously for PMR (PMR(+)) to the remainder of the cohort (PMR(-)).

Of 86 patients with complete follow-up, 13% had been treated previously for PMR. PMR(+) patients had a longer duration of symptoms prior to SVV diagnosis (396 vs. 107 days, p = 0.001) and were less likely to be dialysis-dependent at diagnosis (36% vs. 68%, p < 0.05). Despite the delay in diagnosis, there was a trend towards lower serum creatinine (392 vs. 591 micro M), lower relapse rate (0.04 versus 0.15 episodes/patient-year) and lower incidence of death/end-stage renal failure (27% vs. 53%) in the PMR(+) group.

SVV is frequently misdiagnosed as PMR, especially in those patients with indolent disease, although this did not appear to adversely affect outcome. We recommend that all patients suspected of suffering from PMR undergo careful urinalysis to look for haematuria or proteinuria, and that a low threshold for ANCA testing is maintained.