Clinical and neuroimaging characteristics in neurodegenerative overlap syndrome

Neurodegenerative overlap syndrome has been considered as a wide spectrum of motor neuron disease (MND), parkinsonism, or dementia. Specially, clinically overt parkinsonism occurs more often than expected in patients with motor neuron disease (MND), and diverse clinical manifestations of concurrent parkinsonism have been reported. We aimed to clarify clinical and functional imaging characteristics in patients with combined MND and parkinsonism. Of 732 patients diagnosed with MND over 22 consecutive years, eight patients (all men; mean age 62.8 years) exhibited parkinsonism. According to their parkinsonian features and presence of other neurologic signs including dementia, extraocular movement abnormalities, and cerebellar or autonomic dysfunction, they were classified into two groups: MND-parkinsonism (MND-P, n = 5) and MND-parkinsonism-plus syndrome (MND-Plus, n = 3). In the MND-P group, parkinsonism was asymmetric, dominated by resting tremor, and responsive to levodopa. [18F] N-(3-fluoropropyl)-2β-carbon ethoxy-3β-(4-iodophenyl) nortropane (FP-CIT) positron emission tomography (PET) in two patients disclosed asymmetrically reduced uptakes in the dorsolateral putamen. In the MND-Plus group, parkinsonism was symmetric, with akinetic rigidity and postural instability dominance, and unresponsive to levodopa. [18F] FP-CIT PET scan in one patient showed decreased uptake in bilateral caudate nuclei and putamina. In conclusion, patients with MND and concurrent parkinsonism have heterogeneous clinical and imaging characteristics, which could be classified as features of PD and parkinsonism-plus syndrome. Patients with MND-P may have nigrostriatal dysfunction, and their parkinsonism may respond to levodopa treatment.