Levodopa-responsive Parkinsonism with Normal DAT Scan and Peripheral Synucleinopathy: Benign MSA Versus PD with False Negative DAT?
Virgilio Gerald Evidente1, Todd Levine2, Roy Freeman3, Danica Evidente1, Christopher Gibbons4
1Movement Disorders Center of Arizona, 2Honor Health, 3Beth Israel Deaconess Hosp, 4Beth Israel Deaconess Medical Center
Objective:
To describe the clinical features and skin biopsy of patients with levodopa-responsive parkinsonism with normal dopamine transporter imaging (DaT) scans.
Background:
Multiple System Atrophy (MSA) parkinsonism type (MSA-P) can be mistaken as Parkinson's disease (PD) especially when it presents with asymmetric tremor and bradykinesia. MSA is often suspected if their DaT scans are normal and autonomic symptoms are prominent. Rarely, MSA-P may progress very slowly, and have sustained levodopa-responsiveness and even levodopa-induced dyskinesias. This variant of MSA-P is referred to as Benign MSA.
Design/Methods:
Retrospective chart review of all patients seen in one center from 2012-2024 with levodopa-responsive parkinsonism with normal DaT scans and P-SYN(+) skin biopsies. Patients with dementia and prominent hallucinations were excluded.
Results:
13 patients were identified with average age at time of biopsy=70.2yrs (range-54-83). Mean age at onset of motor symptoms=62.8yrs (range 49-78). Though all 13 had normal initial DaT scans, repeat DaT scans were done in 7/13 patients 1-8yrs later (mean=3.86yrs), of which 3/7(43%) became abnormal. Baseline mean motor UPDRS=28.2(range=12-41). All 13 were treated with levodopa, with all having subjective benefit. Objective mean optimal improvement of motor UPDRS with levodopa was 40% (range-20-62%). 5/13(38%) developed motor fluctuations, whereas 2/13(15%) developed levodopa-induced dyskinesias. Mean total daily levodopa dose at last follow-up was 534.6mg (range 200-1500mg). To date, length of levodopa-responsiveness has ranged from 1-7yrs (mean=3yrs). SCOPA-Autonomic was available for 9/13 with mean=20.6(range=9-30). Cardiac MIBG was done in 8/13: all were either normal or only mildly abnormal.
Conclusions:
Longitudinal follow-up of DAT(-), P-SYN(+) non-demented parkinsonism patients with sustained levodopa-responsiveness reveals that around 1/3 may have abnormal follow-up DAT scans, thus most likely representing PD with initial false(-) DAT scans. The majority though have normal follow-up DAT scans which may represent Benign MSA. The presence of prominent dysautonomia and normal or mildly abnormal cardiac MIBG favor Benign MSA over PD.
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