CYTIDINE DEAMINASE MAY BE A USEFUL MARKER IN DIFFERENTIATING ELDERLY ONSET RHEUMATOID-ARTHRITIS FROM POLYMYALGIA-RHEUMATICA GIANT-CELL ARTERITIS

Objective. PMR/GCA is a relatively common inflammatory disease in the elderly population. Clinical differentiation from a polymyalgic onset of RA in the elderly can be difficult. We have examined in a prelimina ry study the hypothesis that serum cytidine deaminase (CD) may be valu able in the differential diagnosis of these disorders. Methods. CD was assayed by a spectrophotometric method in 20 patients with active PMR /GCA, both before and after treatment with prednisolone, and was compa red with serum CD levels in 20 patients with active RA. Results. CD le vels were within the normal range (< 10 units/ml) in 36 of the 40 samp les from patients with PMR/GCA. The mean CD in pre-treatment samples w as 8.64 units/ml (SD 7.09), and after treatment 7.20 units/ml (SD 3.53 ). The mean serum CD in the RA patients was 21.33 units/ml (SD 8.94), significantly higher than in PMR/GCA (p < 0.0001). Conclusion. Serum C D levels were significantly different when proven PMR was compared wit h established longstanding RA. Therefore, serum CD could be a useful d iagnostic marker for differentiating PMR/GCA from active RA in older p atients.