Steroid-Responsive Parkinsonism and Encephalopathy: A Case Report.

We describe a patient who presented with rapidly progressive parkinsonism and encephalopathy and was diagnosed with seronegative autoimmune encephalitis (AE). Subacute parkinsonism as a manifestation of seronegative AE is uncommon with only a handful of similar cases published in literature. A 71-year-old man presented with severe flu like symptoms, rapidly progressive cognitive decline and was found to have parkinsonian features on examination. Initial brain magnetic resonance imaging (MRI) was unremarkable however, cerebrospinal fluid (CSF) analysis revealed a lymphocytic pleocytosis and elevated protein level. Thorough searches for neural antibodies and infectious pathogens were negative. His symptoms fluctuated initially but markedly improved within days of starting prednisone and dramatically worsened after prednisone was tapered off. His CSF pleocytosis also improved on prednisone. Relapses again resolved with resumption of prednisone. The scope of autoimmune neurology Is constantly evolving, and physicians should be aware of the diverse and heterogenous clinical presentations of autoimmune encephalitis. We aim to emphasize the importance of ruling out autoimmune encephalitis in patients presenting with acute or subacute parkinsonism. This case additionally reinforces that negative antibody tests do not exclude the diagnosis of AE.