A case report of primary CNS lymphoma presenting as rapidly progressive, right-predominant parkinsonism initially misdiagnosed as progressive supranuclear palsy, with diagnosis confirmed by repeat MRI and biopsy and treated with corticosteroids.

Low direct value for Parkinson's therapeutic discovery (no PD mechanisms or targets), but clinically important as a potentially reversible parkinsonism mimic, emphasizing thorough workup and repeat imaging in atypical or rapidly progressing cases.

Primary central nervous system (CNS) lymphoma is an uncommon form of non-Hodgkin lymphoma with a wide range of presentations that can mimic various neurological diseases, including neurodegenerative disorders. We report the case of a 74-year-old man admitted with a seven-month history of progressive cognitive decline and gait disturbances. On examination, he presented cognitive dysfunction, impaired ocular movements, right-predominant parkinsonism, and postural instability. Initial investigations, including imaging studies, electroencephalography, cerebrospinal fluid analysis, and laboratory tests, did not reveal relevant abnormalities, leading to a working diagnosis of probable progressive supranuclear palsy. The patient's condition continued to worsen, and a repeat MRI was performed, revealing findings suggestive of lymphoma. A biopsy confirmed the diagnosis, and corticosteroid therapy was initiated. The patient was subsequently referred to hematology. Although parkinsonism is rarely an initial manifestation of primary CNS lymphoma, the duration and rapid progression of symptoms warranted inpatient investigation, enabling the correct diagnosis and timely initiation of treatment of a potentially curable malignancy.