Is altropane SPECT more sensitive to fluoroDOPA PET for detecting early Parkinson's disease?

Positron emission tomography (PET) cameras are expensive and scarce, and the tests are non-reimbursable. A less costly and more available test such as a single photon emission computed tomography (SPECT) may be helpful in the diagnosis of early or atypical Parkinson's disease (PD) if its sensitivity is comparable to a PET scan. Altropane is an iodinated form of the N-allyl analog of WIN 35,428 which acts as a dopamine transport inhibitor. When radiolabeled with the gamma emitting isotope [123I], altropane serves as a SPECT ligand with high affinity and selectivity for the dopamine transporter. It is a good marker for dopamine neurons and is useful in detecting PD.

We describe 2 patients with typical, early PD and their [123I]-altropane SPECT and [18F]-6-flouroDOPA PET scan results which were performed within a three-month interval. PET studies were performed using a PC-4096 scanner (Scanditronix AB, Sweden) with 15 axial slices and resolution of 6 mm FWHM. The SPECT acquisitions were performed on a MultiSPECT gamma camera (Siemens, Hoffman Estates, IL) equipped with fan-beam collimators with an intrinsic resolution of 4.6 FWHM (for Case 1) and a DSI Ceraspect camera with an annular crystal, with resolution of approximately 6.4 mm FWHM (for Case 2).

Both patients, aged 54 and 38 years, had a one-year history of intermittent right hand tremor with right arm rigidity and hypokinesia and bradykinesia on fine finger movements. A significant and sustained improvement of their parkinsonian symptoms was noted using a dopamine agonist. SPECT and PET scans showed non-diagnostic fluoroDOPA PET scans with clear unilateral striatal reduction of tracer uptake contralateral to their parkinsonian side on altropane SPECT scans.

Altropane SPECT may be an accessible and sensitive imaging modality for detecting early PD. Further and more controlled studies are needed to define its potential role in detecting presymptomatic, early and atypical PD cases.