Striatonigral degeneration (SND) is difficult to diagnose in vivo. The purpose 
of this study was to detect the best indicators for an early and reliable 
diagnosis of the disease. Eighteen patients clinically diagnosed as having SND 
were selected with rigorous inclusion criteria and compared to 18 patients with 
Parkinson's disease (PD) matched for age and disease duration. Apart from 
dysautonomia, the principal discriminant clinical features that distinguished 
SND from PD were the early appearance of the following symptoms and signs: (a) 
severe and atypical progressive parkinsonism characterized by bilateral 
bradykinesia and rigidity, slowness of gait, postural instability, and falls, 
and poor or absent response to adequate levodopa treatment; (b) increased tendon 
reflexes associated or not with frank pyramidal signs, severe dysarthria, and 
less consistently, dysphagia, stridor, antecollis, and stimulus-sensitive 
myoclonus, which, when present, are highly suggestive of the disease.