Drs. Pravin Khemani and Michael Elliot from Swedish Neuroscience Institute in Seattle, Washington, published a case study last month in Parkinsonism and Related Disorders that highlights the role of the Syn-One Test in distinguishing overlapping clinical phenotypes of synucleinopathies from non-synucleinopathies.
The case concerned a 71-year-old male with a several-years-long progressive neurologic condition. Initially, the patient had been seen by a general neurologist for evaluation of ataxia and right arm weakness. Elevated anti-GQ1b antibody led to a diagnosis of Guillain-Barré syndrome, however, treatment with IV immunoglobulin did not lead to an improvement. The patient then underwent spinal surgery to treat weakness in his right arm without any benefit.
The symptoms progressed over three years and the patient was referred to the Movement Disorder program at Swedish Neuroscience Institute.
When the patient reported to the movement disorder clinic, he and his spouse reported impaired gait and balance, slurred speech, urinary incontinence, orthostatic hypotension, and cognitive decline, indicating a widespread neurodegenerative process. The differential diagnosis included neurodegenerative disorders, genetic disorders, autoimmune diseases, and nutritional disorders.
The patient’s DaTscan results were abnormal, potentially supporting a diagnosis of multiple system atrophy (MSA), however, the authors note that similar abnormal results have been reported in cases of spinal cerebellar ataxias (SCAs) with parkinsonism. Therefore, a Syn-One Test was performed, which was negative for phosphorylated alpha-synuclein, reducing the possibility of MSA. Clinicians then ordered whole-genome sequencing and confirmed SCA3 as the cause of the patient’s neurological symptoms, with a specific expansion of 63 CAG repeats (normal, 12–44; intermediate, 45–55; and pathologic, ~56–87 repeats) in the gene encoding ataxin 3 (ATXN3).
This case demonstrates the utility of the Syn-One Test for differentiating between neurological disorders with overlapping clinical features and emphasizes how non-dopamine related disorders can produce abnormal DaTscan results.