Some patients describe this effect as a blurring. PSP patients often show alterations of mood and behavior, including depression and apathy as well as progressive mild dementia. PSP was first described as a distinct disorder in 1964, when three scientists published a paper that distinguished the condition from Parkinson's disease. Although PSP gets progressively worse, no one dies from PSP itself. Approximately 20,000 Americans or one in every 100,000 people over the age of 60 have PSP, making it much less common than Parkinson's disease, which affects more than 500,000 Americans.
Patients are usually middle-aged or elderly, and men are affected more often than women.
PSP is often difficult to diagnose because its symptoms can be very much like those of other, more common movement disorders, and because some of the most characteristic symptoms may develop late or not at all. The most frequent first symptom of PSP is a loss of balance while walking. Patients may have unexplained falls or a stiffness and awkwardness in gait. Sometimes the falls are described by the person experiencing them as attacks of dizziness. This often prompts suspicion of an inner ear problem.