To report 6 cases of patients who underwent brain radiation therapy (RT) before developing parkinsonism.

Reports of radiation-induced parkinsonism are limited and primarily describe levodopa-resistant symptoms.

Case series of patients treated at Memorial Sloan Kettering Cancer Center.

We report 4 women and 2 men who developed parkinsonism 1-7 years following brain RT. One, who underwent resections and RT targeting a pituitary adenoma, exhibited transient parkinsonism without white matter changes or basal ganglia (BG) involvement on MRI which resolved following brief levodopa therapy. Three others proved levodopa-responsive, including patients who (1) underwent whole brain RT as prophylactic cranial irradiation along with lobectomy and chemotherapy for small cell lung cancer and exhibited white matter changes in bilateral periventricular cerebral white matter and pons, (2) underwent resection, chemotherapy and RT targeting a parietal glioblastoma and exhibited hyperintensity extending into left BG, internal capsule and bilateral periventricular and subcortical white matter hyperintensities, and (3) underwent resection, chemotherapy, and RT targeting a parietal glioblastoma and exhibited chronic patchy white matter changes on MRI. A fifth patient, who underwent resections and RT targeting a frontal anaplastic meningioma and did not exhibit white matter changes or BG involvement on MRI, exhibited parkinsonism resistant to levodopa but responsive to amantadine. A final patient, who underwent resection, chemotherapy, ventriculoperitoneal shunt placement, and RT targeting a parafalcine hemangiopericytoma and exhibited confluent bilateral white matter hyperintensity and an enhancing lesion along the septum pellucidum on MRI, exhibited parkinsonism resistant to both levodopa and amantadine.

The medication responsiveness of three of these cases distinguishes them from prior reports. Though potential confounders such as cancer, treatment, and concomitant medical illness complicate definitive symptom attribution, there is likely more variability in radiation-induced parkinsonism, particularly in terms of medication responsiveness, than previously reported. Patients who undergo brain RT should be monitored closely as literature evolves.