The trouble with uric acid crystals, is you know they are there, but you cannot see them.
Also known as gout crystals, these deposits of solid uric acid are too small to see, but devastating in their effects. It’s worrying to know there are millions of tiny particles floating round your body, that remain hidden.
Now, strictly speaking, they don’t always remain hidden, as large deposits form tophi, that can break through the skin. But for our own peace of mind, and to help our doctors diagnosis and treatment, it really is a good idea to see what is happening in our joints.
Traditionally, the only way to test for the presence of uric acid crystals, is to analyze fluid from the joints. Recently, there is hope that DECT might eventually replace this invasive procedure, but the huge expense of suitable scanning equipment puts this beyond the reach of most gout patients.
Advances in other medical imaging techniques lead to frequent reviews in professional journals. The most recent of these concludes:
The diagnosis of gout is usually based on clinical presentation and laboratory findings. Imaging plays a role in the assessment and grading of articular damage related to chronic, long-standing disease, which is characterized by granulomatous synovitis, tophi, and erosions. Multimodality imaging of chronic tophaceous gout may be useful in clinical practice for a variety of purposes, including assessment of disease-related anatomical changes and monitoring of articular and soft-tissue lesions over time, especially in response to urate-lowering therapy. Radiography remains the primary imaging technique. Ultrasonography may detect monosodium urate crystals on cartilage, is helpful to assess small joint effusion, to guide to joint aspiration, and to evaluate the volume of tophi. Computed tomography is considered to be more sensitive than plain radiography in the detection and evaluation of cortical bone erosions associated with tophi. MRI represents the only imaging modality which provides visualization of bone marrow oedema associated with erosions and may be useful to characterize and distinguish tophi from other soft tissue nodules.
Unfortunately the full report is in Italian, and impossible for me to understand. However, an earlier review shows similar findings, and so we can see how different technologies play their part in allowing us to see uric acid crystals (or not).
Uric acid crystals will not show on x-rays. However, they do show joint damage where gout has eaten into the bone. Unfortunately, this is too late to prevent that damage.
The relatively low cost, and high availability, of ultrasound makes it the most reliable tool for measuring gout progression. It will detect deposits at quite an early stage, though it will not determine if these are uric acid crystals from gout or other deposits such as pseudogout. If there is doubt, the ultrasound can also help in positioning the rheumatologist’s needle for joint fluid analysis.
Computed Tomography will detect uric acid crystals at very low volumes. It also shows clearly when these deposits start growing into bone – a much earlier recognition of bone damage compared to x-ray. Though this early detection of deposits allows urate lowering treatment to start before gout causes permanent damage, the scarcity of suitable equipment limits this to the lucky few.
MRI, though not cheap, is more widely available. It will detect bone erosion earlier then x-ray, and it will detect deposits, though not what they are. The 2009 study concludes that MRI might be most useful in assessing joint problems associated with gout, whilst the later report notes that it is the only technique to show bone marrow swelling [edema].
- [Multimodality imaging of chronic tophaceous gout].
- Paparo F, Sconfienza LM, Muda A, Denegri A, Piccazzo R, Aleo E, Cimmino MA.
- Reumatismo. 2010 Oct-Dec;62(4):286-91.
- Imaging of gout: findings and utility.
- Perez-Ruiz F, Dalbeth N, Urresola A, de Miguel E, Schlesinger N.
- Arthritis Res Ther. 2009;11(3):232. Epub 2009 Jun 17. Uric Acid Crystals: X-ray, Ultrasound, MRI, & CT
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