|LETTER TO EDITOR
|Year : 2017 | Volume
| Issue : 4 | Page : 199-200
Dual-energy computed tomographic visualization of urate crystals in a case of familial gout in Western India
Sonal Saran1, Pushpinder Singh Khera2
1 Department of Radiology, Subharti Medical College, Meerut, Uttar Pradesh; Department of Radiology, AIIMS, Jodhpur, Rajasthan, India
2 Department of Radiology, AIIMS, Jodhpur, Rajasthan, India
|Date of Web Publication||16-Oct-2017|
Subharti Medical College, Meerut, Uttar Pradesh
Source of Support: None, Conflict of Interest: None
|How to cite this article:|
Saran S, Khera PS. Dual-energy computed tomographic visualization of urate crystals in a case of familial gout in Western India. Ann Afr Med 2017;16:199-200
Gout is a type of inflammatory arthritis mostly affecting men older than 40 years of age and precipitated by the crystallization and deposition of uric acid within the joints, tendons, and soft tissues. This usually occurs in hyperuricemia.
The mainstay for the diagnosis of gout is demonstration of negatively birefringent, needle-shaped monosodium urate crystals by polarized microscopy in tissue or synovial fluid. Many clinicians do not advice synovial fluid analysis, and treatment is often started with an assumed clinical diagnosis. Dual-energy computed tomography (DECT) can demonstrate uric acid crystals and replace polarized microscopy in many patients.
A 5-year-old girl presented to the orthopedic clinic with the complaints of pain in the right first metatarsophalangeal (MTP) joint for 2 days. The pain was severe in intensity. On clinical examination, there was mild swelling, warmth, erythema, and tenderness in the above joint. Serum uric acid, C-reactive protein, and erythrocyte sedimentation rate were normal (3.9 mg/dL, 0.82 mg/L, and 3 mm in the 1 h, respectively). Serum urea and creatinine were also normal. There was no pain in the small joints of hands and other small joints of feet. Her 45-year-old father was a known case of gout for 20 years and had chronic tophaceous gout.
DECT of both the feet of the father and daughter were performed on Siemens 256 slice Somatom Definition Flash™ computed tomography (CT) scanner with the feature of dual-energy X-ray tube. The reconstructed low- (80 kV) and high-energy (140 kV) images were analyzed by a commercially available software tool (Gout, Syngo CT Workplace; Siemens Healthcare). The software employs a material decomposition algorithm to identify uric acid and calcium voxels according to their material-specific dual-energy behavior [Figure 1]a and [Figure 2].
|Figure 1: (a) Dual-energy computed tomography with three-dimensional reconstruction of the bilateral feet of the daughter showing small green color mapping areas (arrows) in the bilateral first metatarsophalangeal joints, right fifth metatarsophalangeal joint, and left fourth and fifth metatarsophalangeal joints suggestive of urate crystals. Approximate volume: 0.19 cm3. (b) Ultrasound examination of the right first metatarsophalangeal joint showing normal joint space with no evidence of any effusion, synovitis, and urate crystals|
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|Figure 2: Dual-energy computed tomography with three-dimensional reconstruction of the bilateral feet of the father showing large green color mapping areas involving multiple joints, tendons, and soft tissue suggestive of urate crystals forming tophi. Approximate volume: 13.46 cm3|
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An ultrasound examination of the MTP joints of the daughter was also performed with the high-frequency probe [Figure 1]b.
As there was no synovial effusion to aspirate, polarized microscopic analysis of the synovial fluid was not possible. The patient was prescribed anti-inflammatory drugs and asked to report if pain recurs. To the best of our knowledge, this is the youngest reported case of gout in literature with normal renal function.
Relative absorption of X-rays at two energy levels (ideally at 80 and 140 kVp) by the material in question is the fundamental principle behind DECT. Atomic weight and electron density determine the differential attenuation of the material examined.
Several studies have compared the diagnostic accuracy of DECT for the evaluation of gouty arthritis. Ogdie et al. performed a meta-analysis of 11 studies and found a pooled sensitivity and specificity of 0.87 and 0.84, respectively, as compared to polarized microscopy. Bongartz et al. performed a study on forty patients with active gout and 41 individuals with other types of joint disease and found that DECT has sensitivity and specificity of 0.90 and 0.83, respectively. The presence of tophaceous gout was an exclusion criterion in their study, and so the study data were more representative of the early course of the disease.
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[Figure 1], [Figure 2]