Autonomic Testing Profiles in Scans without Evidence of Dopaminergic Deficit (SWEDD)

Background: Scans without evidence of dopaminergic deficit (SWEDDS) on ¹²³I-FP-CIT SPECT (DAT) can occur in patients with clinical evidence of Parkinsonism. In this patient population, autonomic function testing may elucidate the underlying clinical disorder. Objective: To evaluate SWEDD patients undergoing autonomic testing and determine the severity and pattern of autonomic dysfunction. Methods: All patients with a diagnosis of SWEDD and formal autonomic function testing at Mayo Clinic, MN were retrospectively reviewed. Autonomic failure was quantified using composite autonomic severity score (CASS). The Modified Hoehn and Yahr score (HYS) determined Parkinsonism severity. Results: Of 1,874 patients with DAT imaging at Mayo Clinic, 13 met diagnostic criteria of SWEDD. The median age of symptom onset was 56.0 (IQR 40.5-75.5). Autonomic dysfunction was present in 12/13 on ARS and/or TST. The median CASS was 2.50 (IQR 1.00-3.00). Distal anhidrosis was most common (7/13) while 3/13 had widespread anhidrosis on TST and/or QSART testing. Patients with a distal pattern of anhidrosis had a median score of 3.0 (IQR 2.38-4.25) on the HYS versus 2.0 (IQR 1.00-2.00) for those with a diffuse pattern (p=0.048). Patients with more advanced Parkinsonism were more likely to respond to L-Dopa, with higher HYS in the dopa-responsive versus non-Dopa-responsive (p=0.026). No correlation existed between severity of Parkinsonism, and CASS (p=0.39). Conclusion: Autonomic function testing may detect autonomic dysfunction in most patients with SWEDD. The pattern of dysfunction is suggestive of the degree of clinical Parkinsonism, and autonomic testing may predict whether patients with SWEDD respond to L-Dopa.