Which type of gaze limitation occurs in PSP (Prograsdive supra nuclear palsy)
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PSP progressive supranuclear palsy gaze palsy type vertical downward
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Here is a thorough answer on gaze limitation in PSP:
Gaze Limitation in PSP (Progressive Supranuclear Palsy)
The Core Finding: Vertical Supranuclear Gaze Palsy
PSP produces a supranuclear vertical gaze palsy - the most characteristic eye movement abnormality of this disease. The key points:
| Feature | Detail |
|---|---|
| Type | Supranuclear (above the level of CN III/IV nuclei) |
| Direction affected first | Downward gaze (downgaze palsy is the earliest and hallmark finding) |
| Subsequently | Upgaze also becomes impaired |
| Later progression | Horizontal gaze becomes impaired, eventually leading to global gaze palsy |
| Convergence | Paralysis of convergence also occurs |
Why "Supranuclear"?
The lesion is above the oculomotor nuclei (CN III, IV). The underlying pathology involves:
- Tau protein aggregation (neurofibrillary tangles) in the brainstem - specifically degeneration of the rostral interstitial nucleus of the medial longitudinal fasciculus (riMLF), which drives vertical saccades
- The oculomotor nuclei themselves are intact, which is why the doll's eye maneuver (oculocephalic reflex) can initially overcome the gaze limitation (vestibulo-ocular reflex is preserved)
Sequence of Gaze Impairment in PSP
- Early: Slowed and hypometric downward saccades - patients have difficulty looking down (trouble walking down stairs, reading, eating)
- Mid-stage: Upgaze limitation becomes apparent
- Late: Horizontal gaze impairment - loss of horizontal saccades and pursuit
- End-stage: Global gaze palsy (all directions affected)
Clinical Trick to Confirm Supranuclear Level
Because the palsy is supranuclear, the brainstem gaze centers themselves are intact early on. You can demonstrate this by:
- Oculocephalic reflex ("Doll's head maneuver"): Passively moving the head drives the eyes, overcoming the voluntary gaze deficit - confirms the lesion is supranuclear, not nuclear/infranuclear
- This reflex is eventually lost as the disease progresses to affect the brainstem itself
Why Downward Gaze First?
The riMLF contains two populations of burst neurons - those for downward saccades are more vulnerable to tau-mediated neurodegeneration than those for upward saccades. The interstitial nucleus of Cajal (INC), critical for gaze holding in the vertical plane, is also affected.
Associated Ocular Features
- Square wave jerks on primary gaze (common and early)
- Reduced blink rate (parkinsonian feature)
- Eyelid abnormalities: blepharospasm, apraxia of eyelid opening/closing
- Pseudobulbar palsy
Sources:
- Kanski's Clinical Ophthalmology (10th ed.): "Supranuclear gaze palsy, initially primarily of downgaze and subsequently upgaze. Horizontal movements subsequently become impaired, with eventual global gaze palsy."
- Harrison's Principles of Internal Medicine (22E): "Disorders of vertical gaze, especially downward saccades, are an early feature of progressive supranuclear palsy."
- Textbook of Family Medicine (9e): "Patients have ophthalmoparesis of vertical gaze, primarily downward gaze."
Bottom line: PSP = vertical supranuclear gaze palsy, with downward gaze affected first - this is pathognomonic and distinguishes PSP from Parkinson's disease (which does not cause vertical gaze palsy).
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