Late-onset PSP/FTD-like atypical parkinsonism as a novel phenotype of POLG-related disease: a case report.

POLG-related disease is a multisystem mitochondrial disorder that may mimic primary neurodegenerative syndromes. We report a 70-year-old man with progressive cognitive decline, rigid-akinetic parkinsonism, postural instability, vertical supranuclear gaze palsy, and prominent executive and semantic fluency deficits, forming a PSP/FTD-like phenotype. Brain MRI showed frontotemporal-predominant cortical atrophy and a hummingbird sign, while FDG-PET demonstrated frontal and bilateral parietotemporal hypometabolism with preserved occipital metabolism. Alzheimer disease CSF biomarkers were normal and RT-QuIC was negative. Pancytopenia with macrocytosis, liver cirrhosis, and myelodysplastic syndrome indicated multisystem involvement. Genetic testing identified biallelic POLG variants, one pathogenic and one likely pathogenic, confirming POLG-related disease. Levodopa produced partial improvement. This case expands the recognised late-onset POLG spectrum and supports POLG testing in atypical parkinsonism accompanied by cognitive, hepatic, or haematological abnormalities. Early diagnosis may prevent valproate-associated severe hepatotoxicity.