Objective: Characterize patients with unilateral abnormal uptake in DaTscan.

Background: Presynaptic dopamine transporter (DaT) single-photon emission computed tomography (SPECT) imaging is the most used imaging technique to differentiate degenerative parkinsonian syndrome (Parkinson’s disease (PD) and atypical parkinsonian syndromes) from other causes. In PD the common pattern is bilateral and asymmetrical decreased binding in the dorsal putamen, more severe in the contralateral side to clinical symptoms. The clinical significance of strictly unilateral abnormal uptake remains uncertain.

Method: A retrospective analysis was performed for patients who underwent a DaTscan within a tertiary institution between January 1^st and December 31^st of 2021. Information regarding demographic data, clinical features, diagnoses, and treatment was collected.

Results: A total of 141 DaTscans were performed in this period. There were 64 normal scans (45.4%), 40 (28.4%) with bilateral abnormal uptake, 35 (24.8%) with unilateral abnormal uptake and 2 (1.4%) were inconclusive.  
Of those with strictly unilateral abnormal uptake, 20 (57.1%) were male, with a mean age of 68.11 years old. The mean duration of the disease until the exam was 4.7 years. Almost all the imaging abnormalities were classified as “mild” (26, 74.3%) and the side most frequently affected was the right side (23, 65.7%).
Most of the exams was request for investigation of parkinsonian syndromes (23, 65.7%) and for differential diagnosis with essential tremor (6, 17.1%), dystonic tremor (2, 5.7%) or drug-induced parkinsonism (4, 11.4%). The clinician made the diagnosis of probable PD in 14 patients (40.0%), vascular parkinsonism in 3 patients (8.6%), atypical parkinsonian syndrome in 3 patients (two progressive supranuclear palsy and one multiple system atrophy), Lewy body dementia (LBD) in 2 patients (5.7%), and for 13 patients the diagnosis remains uncertain. Twelve patients (34.3%) were on levodopa treatment.

Conclusion: This study enhances the phenotypic heterogeneity of patients with unilateral abnormal uptake. Surprisingly, vascular parkinsonism was only accountable for 8.6% of the cases and there was a large dissociation between clinical signs and DaTscan patterns in the patients with probable atypical parkinsonian syndromes and LBD. The presence of mild abnormal uptake is not synonymous of early PD and, as enhanced in this study, clinical findings play the leading role in the diagnosis.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/the-clinical-challenge-of-an-unilateral-abnormal-uptake-in-datscan/