Marked Decreased Tracer Binding in ¹²³I-FP-CIT SPECT Scans From Lisdexafetamine Dismesylate Interaction: A Case Report

Objectives The objective of this case study is to raise awareness of potential I-123-FP-CIT SPECT interference by lisdexafetamine dimesylate, a prodrug of d-amphetamine. Methods A 69-year-old man with Rapid Eye Movement sleep behavior disorder and mild cognitive impairment had been treated with lisdexafetamine dimesylate for attention-deficit/hyperactivity disorder. The patient had annual or biennial I-123-FP-CIT SPECT evaluations after their baseline visit at 69 years old. Nigrostriatal dopamine transporter uptake was semiquantitatively evaluated with (123I)-FP-CIT SPECT using DaTQUANT 2.0 software. Lisdexafetamine dimesylate was discontinued 3 months before the sixth-year visit (76 years old) by his primary care provider. Results The patient had 4 I-123-FP-CIT SPECT scans with lisdexafetamine dimesylate and 2 scans after the discontinuation of lisdexafetamine dimesylate. The DaTQUANT z-scores of the putamen declined from -1.36 at the baseline visit to -3.02 at the fifth-year visit. After the discontinuation of lisdexafetamine dimesylate, DaTQUANT z-scores of the putamen increased to -0.63 at the sixth-year visit and remained in the normal range of -0.71 at the seventh-year visit. Conclusions This case suggests that lisdexafetamine dimesylate may have a strong interference with (123I)-FP-CIT SPECT, decreasing the tracer binding to the dopamine transporter and presenting false positive results.