[Evaluation of a quantitative diagnostic sacroiliac bone scan index in cases of chronic low back pain in young male adults].

Quantitative bone scan of the sacroiliac joints has long been an established diagnostic method in cases of chronic low back pain (LBP), though its value has been questioned due to the significant overlap of the numerical values between patients with inflammatory sacroiliitis and healthy controls. In an effort to solve this dissent, 133 young male adults aged 18-36 years were studied. We thus aimed to have a relatively homogenous population sample that would include the age that many sacroiliac diseases appear. Thirty-two of our patients had chronic, inflammatory disease of non-infectious origin, as tested by clinicolaboratory procedures (Group A), 29 had mechanical (non-inflammatory type) LBP (Group B), and 72 had been scintiscanned for reasons irrelevant to spine disease (Group C). The members of each group were also classified in three subgroups (a, b and c) according to age. The protocol of planar static multispot bone scan was applied to all three Groups. Three regions of interest (ROI), two on the sacroiliac joints plus one over the L4 vertebra were drawn and finally a non-dimensional numerical parameter called "lambda" was extracted by the equation lambda=total counts/total pixels of the "hottest" of the two sacroiliac joints area divided by the counts/pixels corresponding to the L4 values (lambda=SI/L4). The statistical analysis showed negative correlation of lambda with age in all three groups (P~0.04 for Group A, P~0.012 for Group B and P~0.05 for Group C). When all Groups were examined regardless of age, lambda appeared significantly different (P<0.0005) between Groups A and C, as well as between Groups A and B (P~0.002) but there was no difference between Groups B and C (P~0.12). When the members of each group were analyzed according to age, the paired difference of lambda stirred with remarkable vagueness along the whole spectrum of statistical significance. Conclusively, lambda seems to decrease with ageing at ages ranging from 18 to 36 years (P</=0.05), regardless of the presence of LBP. Additionally, the clinical utility of this parameter seems to be confined to distinguishing patients with LBP due to inflammation from normal people (P<0.0005). This parameter (lambda) may not be used to distinguish patients with LBP of the mechanical type. Using two ROI from the sacroiliac joints instead of one and comparing this to the ROI of the O4 vertebra and also by using a homogenous population one may come to more valid statistics supporting the use of this quantitative factor (lambda), which we describe. To our knowledge, there is no other study of the SI to O4 uptake ratio in young male adults with chronic low back pain mentioned in the literature. A larger population sample would be necessary to accurately standardize the normal value range of lambda. Finally, due to the broad range of normal values of the abovementioned parameter, it is suggested that every nuclear medicine department uses its own normal values of lambda, according to the above methodology.