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22-01-2012 | Immunology | Article

PET imaging predicts clinical arthritis development


Free abstract

MedWire News: Positron emission tomography (PET) can reveal subclinical arthritis in patients with arthralgia, say researchers who believe the imaging technique could allow early treatment intervention.

All patients found to have macrophages using the technique developed clinical arthritis within 14 months of the study, say Conny van der Laken (VU University Medical Center, Amsterdam, the Netherlands) and co-authors.

Macrophages are known to infiltrate synovial tissue in the early stages of rheumatoid arthritis. The team used 11C-(R)-PK11195 (1-[2-chlorophenyl]-N-methyl-N-[1-methylpropyl]-3-isoquinoline carboxamide) PET imaging to examine for the peripheral benzodiazepine receptor, a mitochondrial membrane protein upregulated in macrophages, in the wrists and hands.

Wrist and hand PET was performed in 29 arthralgia patients with anti-citrullinated protein antibodies (ACPAs) but without clinical evidence of arthritis. The PET images were examined by two clinicians, and the patients were followed-up for 2 years for the development of arthritis.

Overall, the two observers had 97% agreement at the patient level, and 99% agreement at the joint level for the presence of macrophages.

Four patients had between one and five PET-positive joints at baseline, increasing to nine patients after 2 years.

All four patients with PET-positive joints at baseline had developed clinical arthritis in the hand or wrist identified by PET by the end of follow-up. Of the five patients with initially negative PET results, two developed hand arthritis and three developed arthritis at sites that were not scanned.

Of note, half of the patients with baseline positive PET scans had an ACPA level above 2500 AU per ml; in comparison none of the 17 patients with negative PET results had an ACPA level above 1000 AU per ml. The median ACPA level for patients with positive and negative PET results were 1180 and 120 AU per ml.

Further investigation should examine the additive value of PET and ACPA level in predicting clinical arthritis, van der Laken et al comment.

"The present study showed good association between macrophage activity on 11C-(R)-PK11195 PET scans of the hands and wrists and subsequent development of arthritis in this region," the team concludes.

Noting there was no clear relationship between PET results and arthritis on the level of individual joints, they comment: "This could be due to waxing and waning of arthritis activity in various joints, which is often observed clinically in developing RA.

"A repeat PET scan over time may add additional predictive power at the joint level."

By Lynda Williams

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