Atypical parkinsonian syndromes
Progressive Supranuclear Palsy and Corticobasal Degeneration
As part of our Planning for the What Ifs series, today we expand the definition of advanced Parkinson’s disease (PD) by discussing atypical parkinsonian syndromes (APS), neurodegenerative disorders that are related to PD. Our guest author, Dr. Pravin Khemani, a Movement disorders neurologist at Swedish Medical Center in Seattle and Medical Director of the APDA Northwest Chapter, will discuss two of these disorders – progressive supranuclear palsy (PSP) and corticobasal degeneration (CBD).
PSP and CBD can mimic each other and can also mimic PD early in the clinical course, so it can be confusing and difficult to diagnose. As the diseases progress however, they produce clinical signs and symptoms which assist in their distinction as separate neurodegenerative disorders. Because there can be a significant overlap between PSP and CBD, it makes sense to discuss them together. Both diseases are caused by abnormal deposition and spread of misfolded tau protein in the brain. Hence, they are referred to as tauopathies.
CBD is less common than PSP, and both are significantly less common than PD. Based on one recent study, the combined number of new cases of PSP and CBD per 100,000 people per year was between 3 and 5. Based on these results, PD is about 5 times more common than these two diseases combined. However these diseases are still seen relatively frequently in Movement disorders clinics and many of our readers are grappling with these conditions.
Progressive supranuclear palsy (PSP):
Since its recognition as a distinct neurodegenerative disorder in 1964, PSP has undergone more than one reorganization into various subtypes based on the increased recognition of its clinical symptoms. In PSP, the distribution of tau protein in specific brain regions is associated with progressive death of neurons which causes clinical signs and symptoms unique to this disorder. The most recent consensus classifies PSP into several clinical subtypes (Table 1). However, the following four primary clinical signs are key features in a majority of cases, although they may not be present all at once in every patient:
Eye movement abnormalities
These are detected by a careful examination which can reveal difficulty shifting the eyes down when not moving the head. Patients may also complain of difficulty walking downstairs, double vision, blurred vision or light sensitivity, and frequent involuntary blinking or forceful closure of eyelids (or blepharospasm).
Early in the disease course when turning, starting to walk or changing position; falls can occur in any direction, but falling backwards is suspicious for PSP.
A feature of PD which can be presented with slowness on one or both sides of the body, soft speech, reduced expression, and stiffness. However, a classic PD rest tremor is uncommon in PSP, and mobility does not show long-term improvement with Levodopa.
Behavioral, speech and cognitive problems early in the course:
impulsive and socially inappropriate behavior
apathy which can be misconstrued as indifference or lack of compassion
inflexibility of thought
laughing or crying out of context (also known as pseudobulbar affect)
difficulty following the steps in a task
stuttering speech with words running into each