Dual-energy CT (DECT) may not have a role to play in the diagnosis of calcium pyrophosphate deposi- tion disease (CPPD), according tostudy findings to be presented during the“Pathological calcification in rheumaticdiseases” Basic and Translational Sciencesession on 5 June.
Dr. Valentin S. Schäfer,associate professor of internal medicine and head ofrheumatology and clinicalimmunology at UniversityHospital Bonn (Germany)will present data showingthat, while DECT had reasonable specificity to ruleout a diagnosis of CPPD(81.8% vs. 100% for gout),it had a sensitivity of only37.5%. The sensitivity ofDECT in detecting gout wasalso lower than that seen inprevious studies, at 59.1%.
Distinguishing between gout and CPPDin the clinic can be challenging, Dr. Schäferobserved in an interview. Both are crystal-induced arthritides and they cause similar,often overlapping symptoms.
“In both diseases, crystal depositioncauses the arthritis. In gout, you haveuric acid deposits that cause the arthritis,[and] similarly, in CPPD, calcium pyrophosphate crystals also cause the arthritis by activation of the immune system,”he explained.
“Both diseases occur very suddenly,with short onset. Patients wake up in themorning and they have a very severe, verypainful, very swollen joint. Most of thetime it’s one or only two joints that areaffected, especially in CPPD,” Dr. Schäferadded.
Clinical suspicion, ultrasound, and x-raysplay an important role in distinguishingbetween the two crystal arthropathies,but the gold standard for confirming a diagnosis of CPPD and gout is arthrocentesiswith subsequent polarisation microscopyto detect calcium pyrophosphate or monosodium urate crystals. “If you see thesecrystals on microscopy, you know 100%that it’s this disease,” he said.
As DECT has been shown to be of
potential use in the diagnosis of gout,
Dr. Schäfer and colleagues wondered if
it could also be a noninvasive means for
detecting CPPD. To investigate, they re-
cruited 30 patients – 22 with suspected
gout and 8 with suspected CPPD – who
underwent DECT and arthrocentesis with
subsequent polarisation microscopy. Re-
sults were also compared with ultrasound,
and suspected clinical diag-
What might seem like a
relatively small number of
CPPD patients is actually
quite large for a tertiary
referral centre, Dr. Schäfer
noted. “CPPD is not a rare
disease, but it’s seldom
seen at a university hospital
[general practitioners] take
care of it, and they give the
patients prednisolone and
ibuprofen, and they don’t come to the uni-
Interestingly, ultrasound was found
to be better than DECT for detecting
both gout and CPPD.
“Ultrasound, which is a noninvasive, immediately available imagingmodality in most European rheumatology clinics, had the highestsensitivity,” Dr. Schäfer said. Thesensitivity in detecting gout was90.9%, and with a “not bad” 75%specificity, “we can immediatelydiagnose the patient with a highsensitivity and also rule out goutwith a relatively high specificity.”Results for CPPD were similar, withan 87.5% sensitivity and a 90.1%specificity.
The suspected clinical diagnosisalso had high sensitivities for detecting both gout (81.8%) and CPPD (75%).
None of the 15 laboratory parametersanalysed, however, including uric acid andthyroid-stimulating hormone, could be associated with either gout or CPPD.
The sensitivity of DECT in the detection
of gout was lower than the 90% seen in
previous studies, Dr. Schäfer observed.
This may be because of the inclusion
of patients with shorter durations of
to form to any significantly detectable
degree in the joints. It could also be be-
cause of how previous studies compared
DECT with the suspected clinical diagno-
sis rather than arthrocentesis as in this
The bottom line is that “DECT is not areally helpful tool for CPPD. Looking at[DECT’s] sensitivity of below 40%, arthrocentesis in CPPD patients plays still quitean important role,” he said. The nextsteps are to perform some subanalysesand include data on more patients withCPPD, and then of course to publish thesedata.
The study had no outside source offunding. The authors declared having norelevant disclosures.
Dual-energy CT does not aid CPPD diagnosis
Gout tophus formation (curved arrows)shown on 80-kV DECT (A) with colour-coded overlay (B) showing monosodiumurate crystals in green and calcium in blue,as well as articular and juxta-articularosseous erosions (straight arrows).
DECT image (A) shows typical findings of CPPDalong the medial and lateral menisci (arrow) withcolour-coded overlay (B) showing calcium intissues where it’s not usually found (e.g., hyalinecartilage).