Purpose: Even though [(123)I]FP-CIT SPECT provides high accuracy in detecting nigrostriatal cell loss in neurodegenerative parkinsonian syndromes (PS), some patients with an inconclusive diagnosis remain. We investigated whether the diagnostic accuracy in patients with clinically uncertain PS with previously inconclusive findings can be improved by the use of iterative reconstruction algorithms and an improved semiquantitative evaluation which additionally implemented a correction algorithm for patient age and gamma camera dependency (EARL-BRASS; Hermes Medical Solutions, Sweden).
Methods: We identified 101 patients with inconclusive findings who underwent an [(123)I]FP-CIT SPECT between 2003 and 2010 as part of the diagnostic process of suspected PS at the University of Munich, and re-evaluated these scans using iterative reconstruction algorithms and the new corrected EARL-BRASS. Clinical follow-up was obtained in 62 out of the 101 patients and constituted the gold standard for the re-evaluation to assess the possible improvement in diagnostic accuracy.
Results: Clinical follow-up confirmed the diagnosis of PS in 11 of the 62 patients. In patients in whom both visual and semiquantitative analysis showed concordant findings (48 patients), a high negative predictive value (93 %), positive predictive value (100 %) and accuracy (94 %) were found, and thus a correct diagnosis was obtained in 45 of the 48 patients. Among the 14 patients with discordant findings, the additional semiquantitative analysis correctly identified all five of nine patients patients without PS by nonpathological semiquantitative findings in visually pathological or inconclusive scans. In contrast, four of the remaining five patients with decreased semiquantitative values but visually normal scans did not show a PS during follow-up.
Conclusion: The age-corrected and camera-corrected mode of evaluation using EARL-BRASS provided a notable improvement in the diagnostic accuracy of [(123)I]FP-CIT SPECT in PS patients with previously inconclusive findings. The gain in accuracy might be achieved by better discrimination between physiological low striatal [(123)I]FP-CIT binding due to age-related loss of the dopamine transporter or pathological loss of binding.
Keywords: Diagnostic accuracy; EARL-BRASS; Parkinsonian syndromes; [123I]FP-CIT SPECT.