Phosphorus-31 magnetic resonance spectroscopy of experimentally induced arthritis in rats.

Phosphorus-31 magnetic resonance spectroscopy (MRS) of the hind paws of rats was performed at 1.5 Tesla before and during the course of an experimentally-induced inflammatory arthritis. Arthritis was induced by daily subcutaneous administration of 6-sulfanilamidoindazole, an antibacterial sulfa known to produce an acute, self-limited arthritis and periarthritis in the hind paws of rats. Phosphorus-31 spectra obtained after the development of clinical arthritis showed a significant (p less than 0.01) increase in the intensity of a group of resonances occurring downfield from phosphocreatine as compared to spectra obtained before treatment. In all rats, this increase correlated well with histological evidence of inflammation as well as with the degree of inflammation judged clinically (r = 0.89, p less than 0.001), and was present before roentgenographic evidence of bony involvement. The use of 31P MRS may permit evaluation of the severity of an inflammatory arthritis with greater accuracy than the bony changes definable by plain roentgenograms.