The gold standard for establishing the diagnosis of gouty arthritis is the detection of monosodium urate (MSU) crystals in synovial fluid or periarticular tophi. The European League Against Rheumatism recommendations from 2006 state that ‘for typical presentations of gout a clinical diagnosis alone is reasonably accurate but not definitive without crystal confirmation’.1 In addition, various imaging methods can help to non-invasively support the diagnosis of gout. Joint ultrasonography can detect MSU deposits at cartilaginous surfaces (‘double contour sign’) as well as periarticular tophus formation.2 3

Dual energy CT (DECT) is an imaging method that uses x-ray beams of two different energies to differentiate MSU deposits from connective tissues and from calcium containing structures by their absorption properties.4 Choi et al have demonstrated that in tophaceous gout, DECT reliably detects clinically overt tophi and subclinical urate deposition sites in these patients.5

Here, we investigate the utility of DECT in patients with the diagnosis of acute gout but without any clinical signs of tophus formation. Over a period of 6 months, DECT examination of the most prominently involved joint regions was performed in 14 consecutive patients with acute gouty arthritis. The diagnosis in these patients was based on microscopic detection of MSU crystals or a recently published clinical score.6 Informed consent was obtained from all patients included in this study, which was reviewed by our institutional review board and considered a diagnostic procedure for patient benefit.

DECT scans were performed with a second-generation 128-slice dual source CT system (Definition Flash; Siemens Healthcare, Forchheim, Germany). The obtained data sets were analysed using a three-dimensional material decomposition algorithm allowing colour coded visualisation and differentiation of MSU (green) from calcium (purple or grey). The total volume of MSU deposits was determined automatically. Radiation exposure of DECT amounts to 0.1–0.2 mSv per examined region. The principle of simultaneous acquisition of two image series using x-ray sources with different energies is mainly used to detect arterial calcifications and is therefore available in many academic clinical institutions. With only minor software adaptations, DECT can be applied to detect and quantify MSU deposits in periarticular tissues.

The clinical data and DECT findings are summarised in table 1. Eleven of 14 patients with acute gout had periarticular or peritendinous MSU deposits detected by DECT (figure 1A–D). The total volumes of MSU deposits for various anatomical regions examined are given. In four patients, the current attack represented the first manifestation of their disease.

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Figure 1

Dual energy CT images of urate deposits in patients with acute gout symptoms. (A) Multiple urate deposits next to the tibiotalar, fibulotalar and subtalar articulations and at the metacarpophalangeal (MCP) 1 and interphalangeal 1 joints (patient 7). The faint green colouring below the calcaneus is an artefact caused by hyperkeratosis and dirt within the thick corneal layer of the heel pad. (B) Linear urate deposits at the patellar and tibial insertion sites of the patellar ligament (patient 10). (C) Linear urate deposits at the calcaneal insertion site of the Achilles tendon and proximal along the tendon (patient 3). (D) Dotted deposits around MCP 3 joint (patient 13).

These data show that MSU deposition may start early in the disease process and can be visualised by DECT. Thus, DECT may be a helpful imaging method for tophus assessment and follow-up in clinical trials as well as during urate lowering therapy in patients with the established diagnosis of chronic gout.7,–,9 It could also be a valuable diagnostic tool in patients with ‘unclassified’ acute or relapsing arthritides.