Levodopa intolerance as a potential clinical red flag for neuronal intranuclear inclusion disease (NIID) in atypical parkinsonism: a case report

This case highlights that profound levodopa intolerance in patients with atypical parkinsonism, especially when accompanied by severe gastrointestinal dysfunction and early cognitive decline, should prompt consideration of NIID. Early recognition of this clinical pattern, together with characteristic MRI findings and confirmatory pathology/genetics, may help reduce diagnostic delay and facilitate timely multidisciplinary supportive care.