What Is Progressive Supranuclear Palsy?

Progressive Supranuclear Palsy (PSP) is a rare neurodegenerative disorder that affects movement, balance, vision, speech, and cognition. It is often misdiagnosed in its early stages as Parkinson's disease due to overlapping symptoms such as stiffness and slowness. However, PSP progresses more rapidly and has distinct features, particularly involving eye movement abnormalities.

The Role of Tau Protein in PSP

A hallmark of progressive supranuclear palsy is the abnormal accumulation of a protein called tau in specific brain regions. Tau normally helps stabilize microtubules within neurons, but in PSP, it becomes misfolded and clumps together, forming neurofibrillary tangles. These tau deposits are primarily found in the basal ganglia, brainstem, and cerebellum, leading to the progressive degeneration of neurons that control balance, eye movements, and cognition.

Slow Eye Movements: A Key Symptom

One of the earliest and most distinctive signs of PSP is slow eye movements, particularly vertical gaze palsy. Patients often have difficulty looking up or down, and their saccades (rapid eye movements between targets) become slow and imprecise. This symptom is a critical diagnostic clue that helps differentiate PSP from other parkinsonian disorders. As the disease advances, voluntary eye movements may become completely impaired, though reflexive eye movements (such as the doll's eye maneuver) often remain intact.

Other Common Symptoms

Beyond slow eye movements, individuals with PSP experience frequent falls, stiffness (especially of the neck and upper body), slurred speech, difficulty swallowing, and personality changes such as apathy or impulsivity. Cognitive decline—resembling frontotemporal dementia—can also occur, including problems with executive function and memory.

Diagnosis and Treatment

Diagnosis of progressive supranuclear palsy relies on clinical evaluation and ruling out other conditions. Brain imaging may show atrophy in the midbrain (often described as a "hummingbird sign"). There is no cure for PSP, and no treatments can stop tau accumulation. Management focuses on symptom relief—such as using assistive devices for falls, speech therapy, and medications for stiffness (though response to levodopa is typically poor).

Outlook and Research

PSP is relentlessly progressive, with average survival of 6 to 9 years from symptom onset. Current research aims at targeting tau pathology—including tau aggregation inhibitors and immunotherapies—to slow or halt the disease. Advances in neuroimaging and biomarkers are also improving early diagnosis. Understanding the role of tau in PSP may eventually benefit related tauopathies such as Alzheimer's disease.