**5. Infection**

102 12 Chapters on Nuclear Medicine

The immunoscintigraphy has proven to be more sensitive than clinical examination for identifying synovitis and have a high positive predictive value for the onset of RA in patients with nonspecific arthropathy, and its usefulness for monitoring and assessing treatment response (Colamussi et al., 2004; as cited in De Bois et al., 1995a, 1995b, 1996). It can also be used to detect infection, although the preferred technique in these cases is labelled leukocyte scintigraphy, in which two tracers are often used: 99mTc-HMPAO or 111In-oxine (De Gersem & Jamar, 2010). Labelled leukocyte scintigraphy is also useful in assessing therapeutic response in RA patients and it has been correlated with other indices of activity in this disease (Collamussi et al., 2004; as cited in Al-Janabi et al., 1988). However, immunoscintigraphy seems to be more accurate than labelled leukocyte scintigraphy for the identification of synovitis in RA (Collamussi et al., 2004; as cited in Liberatore et al., 1992). Other molecules and receptors (e.g. 64Cu-labelled anti-GPI, 68Ga-labelled annexin V or 123I-antileukoproteinase) are being identified as therapeutic targets and used to develop new radiopharmaceuticals which accumulate in areas of inflammation where they can be located and quantified. Their study and description will allow improving the understanding of the complex pathophysiology of RA and detecting changes in very early stages of this disease and will give us the possibility of a pre-therapy scintigraphic approach with radiolabelled monoclonal antibodies that will let us evaluate the presence of target molecules in the inflammatory lesion, thus helping in the selection of the most efficient therapy and predicting therapy response (Glaudemans et al., 2010; Malviya et al., 2010). But currently, these techniques are not used in clinical practice and remain like a research tool inside selected laboratories. Bioluminescence and fluorescence reflectance imaging are other approaches that allow imaging, and potentially the delivery of therapeutic agents at a

Sacroiliac joint involvement is a common finding in the spondyloarthropathies (SpA) group and it is an important parameter included in the diagnostic criteria. Conventional radiology is essential in the evaluation of the sacroiliac joints, but it does not detect early abnormalities and, therefore, the use of other complementary techniques currently available, such as CT,

Until only a few years ago, bone scintigraphy was the gold standard technique for early diagnosis of inflammatory processes at this joint. The assessment of sacroilitis by scintigraphy is based on the quantification of radiotracer uptake in the sacrum and sacroiliac joints. This technique can help to differentiate between degenerative and inflammatory disorders in patients with nonespecific radiological changes. Both conventional bone scintigraphy and SPECT mode are sensitive techniques for early detection of SpA in patients with low back pain and who still do not have typical radiological changes, because the uptake of radiopharmaceutical at sacroiliac joints is produced before structural damage happens. However, in the sclerotic phase of evolved SpA, scintigraphy frequently does not detect any abnormalities. MRI, more sensitive in detecting early changes and more specific, has shifted to the bone scan. In this regard, a published review (Schneider, 2006; Song et al., 2008) realized with the aim to assess the diagnostic value of scintigraphy for detecting sacroilitis in patients with established and/or probable ankylosing spondylitis, has proven limited value of scintigraphy both in the early detection of sacroilitis and in patients with established ankylosing spondylitis. In patients with SpA and gastrointestinal symptoms but

MRI, US, and bone scintigraphy, is necessary to avoid delaying the diagnosis.

molecular level (McQueen & Ostergaard, 2007).

**4. Sacroilitis** 

In the setting of infection four entities can be established: osteomyelitis, septic arthritis, soft tissues infections and joint replacement infection.
