The role of ¹²³I-FP-CIT-SPECT in the differential diagnosis of Parkinson and tremor syndromes: a critical assessment of 125 cases

¹²³I-FP-CIT-SPECT is useful in the differential diagnosis of Parkinson’s disease (PD) and tremor syndromes. Recently, there have been reports on normal nigrostriatal uptake of radio ligands in PD patients, referred to as scans without evidence of dopaminergic deficit (SWEDDs). Furthermore, a dopaminergic deficit has been described in some cases of different tremor types. We sought to clarify the occurrence of SWEDDs in PD and a possible association of various tremor types with PD. We performed a retrospective case analysis of 125 patients with diagnostically uncertain Parkinsonian or non-Parkinsonian tremor syndromes with clinical assessments and ¹²³I-FP-CIT-SPECT. A total of 36/40 (90%) patients with the predominant clinical feature of a postural and/or kinetic tremor showed normal DAT SPECT; 73/85 (86%) with predominant clinical symptoms of PD showed abnormal DAT SPECT with lower overall radio ligand uptake and a significant asymmetry contralateral to the clinically more affected side. In all, 4/40 (10%) of non-Parkinsonian tremor patients had abnormal DAT SPECT, but no corresponding asymmetry of radio ligand uptake. Probable essential tremor was considered clinically in follow-up assessments although final diagnosis of these four tremor cases remains inconclusive. A total of 12/85 (14%) clinically suspected PD patients had normal DAT SPECT (SWEDDs). Clinical reassessment identified two patients with dystonic tremor. Five patients with a positive response to levodopa remained unclear. In four cases of suspected PD with normal DAT SPECT, non-neurologic diseases were identified. One case showed a complete and spontaneous remission of symptoms. DAT SPECT offers an objective method to confirm or exclude a dopaminergic deficit in tremor predominant parkinsonism for clinically inconclusive cases. There was no evidence of a decrease in DAT binding in the majority of patients with postural and/or kinetic tremor. The striatal asymmetry index is a further helpful tool for differentiating PD from non-PD tremor syndromes.