Radiation therapy-related ataxia associated with FDG-PET cerebellar hypometabolism

Brain FDG-PET after radiation therapy is classically used to differentiate between tumor recurrence and radiation-related tumor necrosis. Little is known about FDG-PET in patients with radiation-induced leukoencephalopathy without radiological aspect of necrosis. We present a 69-year-old woman who had preventive whole brain radiation after a diagnosis of paraneoplastic Lambert-Eaton syndrome related to small cell lung cancer. Five months after radiation therapy, she developed radiation-induced leukoencephalopathy manifested by ataxia. Profound cerebellar hypometabolism on FDG-PET was in contrast with the presence of only discrete cerebellar white matter changes on MRI. FDG-PET abnormalities seem to correlate better with clinical signs related to radiation-associated brain toxicity than MRI.