Distal symptoms and signs can be identified in up to one-half of patients with PMR—carpal tunnel syndromes, distal arthralgias, and a modest peripheral arthritis, most common at metacarpophalangeal and wrist joints, as briskly responsive to low-dose CS as are the proximal symptoms, and never erosive. A positive anti-CCP antibody will flag a diagnosis of rheumatoid disease in a patient with a polymyalgic presentation and distal findings. But polyarthritis of abrupt onset in older adults is not uncommonly seronegative, and clinical and serologic attempts to differentiate PMR at presentation from something that is better construed as rheumatoid disease have not been particularly successful. Practically speaking, it may take three to six months of attentive follow-up to sort things out; if peripheral arthritis recurs with efforts to get the dose of prednisone below 10 mg per day in a patient initially thought to have PMR, the diagnosis—and therefore treatment—must be reassessed. A reliable biomarker for PMR—or set of such markers—would obviously be a boon.
Considering GCA
What PMR, a musculoskeletal problem with a special predilection for the synovium of the proximal joints and bursae, has to do with GCA, a systemic granulomatous arteritis, is a mystery. Their epidemiologic relationship has already been touched on. A striking feature of GCA is the heightened prevalence in Scandinavians, and its decidedly uncommon occurrence in African-Americans—a genetic clue that remains to be deciphered.8 Data for such prevalence in PMR are not available, but clinical experience suggests that both PMR and GCA are much more common in Northern Europeans than African-Americans and Latinos. That said, all ethnic and racial groups can be affected—indeed, my patient whose GCA went undiagnosed was of African origin, by way of Barbados and, before that, the slave trade from West Africa.
The Diagnosis of GCA
The diagnostic stakes in GCA are of course much higher than in PMR, because of the potential consequences of a missed diagnosis—loss of vision—and the potential toxicities of the treatment that ensues—customarily, high-dose CS. I remain of the opinion that GCA is not a clinical diagnosis, and that every effort should be made to premise this diagnosis on histopathological—or additional—footing. The traditional means of securing histopathological evidence is the humble temporal artery biopsy, which is minimally invasive, simple, and benign. However, the performance of the temporal artery biopsy as a diagnostic test is beset with, as my granddaughter puts it, issues. What length? One side? Both sides? Simultaneous? Sequential? My eminence-based take is that, in the appropriate clinical context, a unilateral, shorter segment biopsy has a high negative predictive value for the diagnosis of GCA—but it is unlikely that the merits and deficiencies of the temporal artery biopsy are amenable to definitive resolution.
