Introduction: The D(2) receptor is the most widely expressed dopaminergic receptor in the central nervous system, and it is present at the pre- and postsynaptic dopaminergic regions. It is mainly located in the neostriatum as well as in the globus pallidus, substantia nigra, cerebral cortex, thalamus, etc. The objective of this study was to analyze qualitatively and quantitatively the distribution pattern of the postsynaptic dopamine receptors through SPECT with iodobenzamide (IBZM) in patients with parkinsonism and to determine the benefit of this imaging technique in the differential diagnosis of the parkinsonian syndromes.
Materials: A total of 26 patients with clinical and imaging (Iodine-123 fluoropropyl-carbomethoxy-3 beta-(4-iodophenyltropane) [FP-CIT]) diagnostics of parkinsonism, to all of which a study of postsynaptic D(2) receptors with IBZM was made, were retrospectively reviewed. Of total, 12 patients were male (42.85%). The average age was 73 years old (range, 64-83 years). The patients were imaged using SPECT 2 hours after administration of I-123 Iolopride (IBZM) and their images were evaluated qualitatively and quantitatively. To measure the relative density of the D(2) receptors, the studies were registered to a common space in which the structures to be analyzed were delimited over a RM template. Caudate/frontal (C/FI) and putamen/frontal (P/FI) activity indexes were obtained.
Results: Of total, 10 patients presented normal IBZM uptake (C/FI of 1.23 + or - 0.13; P/FI of 1.53 + or - 0.11). The 16 studies listed as abnormal were divided into 2 degrees: (I) appearance of thalamic activity with preserved striatal uptake and (II) thalamus and frontal increased uptake with decrease of striatal activity. In the patients with abnormal patterns, the region that showed a greater reduction of uptake was the putamen (P/FI of 1.1 + or - 0.07 for degree 1, P < 0.05 and P/FI of 1.25 + or - 0.19 for degree 2, P < 0.001). For the differential diagnosis of Parkinson disease in relation to the atypical parkinsonisms, the sensitivity was 68.4% (confidence interval, 51.9-87.6) and the specificity was 57.1% (confidence interval, 20.2-88.2). The patients with Parkinson disease with longer evolution times showed a decrease of D(2) activity (3/7).
Conclusion: The appearance of thalamic activity may be an early indicator of a decrease of D(2) striatal receptors in atypical parkinsonisms and in patients with long-term Parkinson disease.