Prof Nicola Dalbeth
Dual-energy CT can help in the diagnosis and management of gout and shows promise as a prognostic and educational tool, according to Professor Nicola Dalbeth, a rheumatologist at the University of Auckland.
Speaking at EULAR 2018 in Amsterdam, Prof Dalbeth said dual-energy CT could be useful in situations where it is difficult to obtain a sample of aspirated synovial fluid for urate and microscopic examination of the affected joint for crystals. This might occur if it is not possible to insert a needle into the affected joint to retrieve a sample, if the patient is anticoagulated or there is surrounding infection, or when analysis of the aspirated synovial fluid returns a negative result despite a high suspicion of gout.
“Dual-energy CT is a really useful tool then to identify urate crystals and virtually all of those patients who have urate crystal deposition in that situation will also have microscopically proven disease on subsequent testing,” Professor Dalbeth said in an exclusive interview with the limbic.
“It’s really in those situations where there is diagnostic uncertainty. I don’t think dual-energy CT is something we need to do for every patient with gout, but I think it is a really useful tool when we just don’t know or it’s an unusual clinical situation.”
The technique is also useful to assess inaccessible sites, for example to visualise deposits and tophi on the spine, and Professor Dalbeth predicts it will be used in this way more frequently in future.
Another potential use for the dual energy CT is in monitoring the treatment response, she believes. Where a patient has been on urate-lowering therapy for many years, is not experiencing flares and doesn’t have tophi, dual-energy CT may be used to assess whether it is feasible to reduce the dosage of anti-gout medication or stop it completely.
“Scanning patients in that situation to actually demonstrate complete resolution of crystal deposits might provide us with some more kind of therapeutic certainty about that,” she suggests.
“We don’t have good prospective studies to show that that is an appropriate tool, but I think that’s where we’re heading.”
Dual-energy CT may also be of benefit in future as an indicator of likely disease prognosis. Around one in four patients with very high serum urate concentrations will show urate crystal deposition when scanned, notes Professor Dalbeth.
“It may be that those people are more likely to develop disease or are more likely to develop joint damage or flares in future. We really need those prospective studies to determine whether this is a prognostic indicator for people with asymptomatic hyperurcaemia.”
The images of urate crystals produced by dual-energy CT also provide a very powerful educational tool for both physicians and patients.
“I have learnt an enormous amount about the disease by seeing these images,” she says.
Gout has a tendency to be seen as an acute flaring disease, but “when you actually see the scans of people who aren’t flaring and there is crystal deposition I think it really helps us as clinicians and also patients to understand that this is a chronic disease of crystal deposition and actually provide a cognitive rationale for urate lowering therapy long-term,” Professor Dalbeth concludes.