Procerus sign as a diagnostic clue for progressive supranuclear palsy.

The procerus sign is associated with some diseases that initially manifest as atypical parkinsonism, especially progressive supranuclear palsy (PSP). It is described as a vertical contraction of the muscles in the glabellar region. This sign helps to clinically differentiate atypical parkinsonism diseases, especially in the early stages, when many conditions are similar, in terms of clinical presentation and poor response to levodopa. Thus, the procerus sign can be an important clue in the suspicion of PSP.