Parkinsonian traits in amyotrophic lateral sclerosis (ALS): a prospective population-based study

Background: Amyotrophic lateral sclerosis (ALS) is characterized by a spectrum of phenotypes, but only a few studies have addressed the presence of parkinsonian (PK) symptoms. The aim of our study was to investigate the occurrence of PK features in a prospective population-based cohort of ALS patients, determining their demographic, clinical, neuropsychological and genetic characteristics, and identifying their morphological and functional imaging correlates. Methods: A consecutive series of ALS patients were enrolled and prospectively followed for 2 years. Patients were classified according to the presence (ALS-PK) or absence (ALS) of PK signs, and they underwent neuropsychological testing, genetic analysis for the main ALS and PD genes, brain MRI and ¹⁸ F-FDG-PET. ALS-PK patients underwent ¹²³ I-ioflupane SPECT. Results: Out of 114 eligible patients, 101 (64 men; mean age at onset 65.1 years) were recruited. Thirty-one patients (30.7%) were classified as ALS-PK. Compared to ALS patients, ALS-PK patients were more frequently male, but did not differ for any other clinical, demographic or neuropsychological factors. ¹²³ I-ioflupane SPECT was normal in all but two ALS-PK patients. At ¹⁸ F-FDG-PET, ALS-PK patients showed a relative hypometabolism in left cerebellum and a relatively more preserved metabolism in right insula and frontal regions; MRI fractional anisotropy was reduced in the sagittal stratum and increased in the retrolenticular part of the internal capsule. Conclusions: In our study, about 30% of ALS patients showed PK signs. Neuroimaging data indicate that PK signs are due to the involvement of brain circuitries other than classical nigrostriatal ones, strengthening the hypothesis of ALS as a complex multisystem disease.