To scan or not to scan

The Food and Drug Administration (FDA) recently approved [¹²³I]ioflupane ([¹²³I]-fluoropropyl βCIT), a dopamine transporter (DAT) radioligand, for SPECT to “assist in the evaluation of adult patients with suspected parkinsonian syndromes (PS).”¹ This permits physicians to prescribe [¹²³I]ioflupane SPECT scans as part of clinical practice. Advertisements encourage clinicians to order this and patients to request such scans. The key questions for neurologists are as follows: Do [¹²³I]ioflupane SPECT scans provide useful data beyond clinical evaluation? Does this information improve patient care?

SPECT measurement of the striatal uptake of [¹²³I]ioflupane reflects the integrity of terminal fields of nigrostriatal neurons. People with Parkinson disease (PD) have reduced striatal uptake.^2,3 In fact, such scans may be more sensitive than the clinical examination to detect nigrostriatal defects.⁴ However, loss of striatal DAT occurs in most degenerative PS, including multisystem atrophy (MSA), progressive supranuclear palsy (PSP), and corticobasal disease (CBD).⁵ Thus, in individual cases, reduced striatal uptake of [¹²³I]ioflupane does not distinguish these different conditions. Most clinical studies focused on whether these scans reliably discriminate PS from disorders that clinically resemble PS but without striatal DAT deficiency.

Multiple studies report that DAT SPECT can distinguish PS from essential tremor (ET). ET is chosen as the comparator disorder for many studies since it has normal striatal DAT. The first published study compared DAT SPECT with initial and 6-month follow-up examinations by a movement disorders expert.⁶ The goal was to determine whether SPECT predicts the follow-up clinical diagnosis. The subjects had either PS …