Evidence for a dopaminergic deficit in sporadic amyotrophic lateral sclerosis on positron emission scanning

Although rare, the chronic neurodegenerative disorders amyotrophic lateral sclerosis (ALS) and idiopathic parkinsonism coexist to a greater degree than expected by chance. This suggests that patients with ALS may have subclinical lesions of the nigrostriatal dopaminergic pathway. To study this hypothesis, we did positron emission tomography with 6-fluorodopa on 16 patients with sporadic ALS and without extrapyramidal disease, and compared the results with age-matched controls. We found a significant progressive fall in 6-fluorodopa uptake with time since diagnosis, and reduced dopaminergic function in 3 patients with ALS of long duration. This supports the hypothesis that ALS and IP may share pathogenesis and, perhaps, aetiology.