The role of radiotracer imaging in Parkinson disease

To the Editor:

Ravina et al.¹ performed a review of functional imaging as a marker of disease activity and progression and as a diagnostic tool in Parkinson disease (PD). Diagnostic sensitivity and specificity were incorrectly attributed to beta-CIT SPECT. They referred to work with the FP-CIT ligand.^2,3 This compounds a similar error in another recent review.⁴ FP-CIT is licensed in Europe (DaTSCAN, GE Healthcare) for patients with clinically uncertain Parkinsonian syndromes to aid the differential diagnosis of PD and tremor disorders, and has already been applied to several of the very valid questions raised in the article.

We agree that “most diagnostic studies have been small, single center studies of patients with probable Parkinson disease” but this statement omits the larger dual and multi-center studies with FP-CIT. One hundred and eighty-nine diagnostically uncertain Parkinsonian patients^2,5 have been specifically selected for study with FP-CIT. Our prospective study of 62 early and diagnostically uncertain cases reported with initial 3 months' follow-up² is ongoing. A further multi-center project shows increased congruence of the clinicians' diagnosis to the baseline FP-CIT SPECT image at 18 months, in 180 patients (European FP-CIT study group, unpublished observations).

In accordance with other neuroimaging studies when baseline FP-CIT …