["Red flags": when to be alerted and how to explore?].

The diagnosis of Parkinson's disease (PD) requires ruling out other causes of parkinsonism. Among various "other" causes of parkinsonism, neurodegenerative causes or "atypical parkinsonism" are the most difficult to diagnose. Most common diseases are "synucleinopathies": multiple system atrophy and dementia with Lewy bodies and "tauopathies": progressive supranuclear palsy and corticobasal degeneration. Unexpected or atypical signs and symptoms for PD, also called "red flags" along with absent or poor or short-lived levodopa response may be a clue for the diagnosis. Some tests may also support the diagnosis, among them, structural (MRI) and functional brain imaging, autonomic function tests and urodynamics, oculographic recordings and neuropsychological work-up, are the most useful.