PSP and Idiopathic Normal Pressure Hydrocephalus: Clinical Overlap and Comorbidity

PSP and Idiopathic Normal Pressure Hydrocephalus: Clinical Overlap and Comorbidity

Overview

Idiopathic Normal Pressure Hydrocephalus (iNPH) is a treatable cause of gait disturbance, cognitive decline, and urinary incontinence in older adults. Emerging evidence demonstrates that iNPH frequently coexists with neurodegenerative movement disorders, particularly [Progressive Supranuclear Palsy](/diseases/psp) (PSP), [Parkinson Disease](/diseases/parkinsons-disease), and [Multiple System Atrophy](/diseases/multiple-system-atrophy). This page synthesizes the current evidence regarding the clinical, imaging, and pathological overlap between PSP and iNPH, with implications for diagnosis and management[@pmid31959516].

Epidemiology of PSP-iNPH Comorbidity

Prevalence and Frequency

The coexistence of iNPH with neurodegenerative disorders is more common than previously recognized:

• Studies report that 6-18% of patients with clinically diagnosed iNPH have concurrent neurodegenerative disease[@shimada2025]
• Autopsy series reveal that up to 30% of iNPH cases show comorbid tauopathy or synucleinopathy[@agerskov2024]
• PSP-iNPH comorbidity appears to be particularly frequent, given shared vulnerability of brainstem and subcortical structures[@shimada2025]

Clinical Implications of Comorbidity

The presence of both conditions presents diagnostic challenges:

...

PSP and Idiopathic Normal Pressure Hydrocephalus: Clinical Overlap and Comorbidity

Overview

Idiopathic Normal Pressure Hydrocephalus (iNPH) is a treatable cause of gait disturbance, cognitive decline, and urinary incontinence in older adults. Emerging evidence demonstrates that iNPH frequently coexists with neurodegenerative movement disorders, particularly [Progressive Supranuclear Palsy](/diseases/psp) (PSP), [Parkinson Disease](/diseases/parkinsons-disease), and [Multiple System Atrophy](/diseases/multiple-system-atrophy). This page synthesizes the current evidence regarding the clinical, imaging, and pathological overlap between PSP and iNPH, with implications for diagnosis and management[@pmid31959516].

Epidemiology of PSP-iNPH Comorbidity

Prevalence and Frequency

The coexistence of iNPH with neurodegenerative disorders is more common than previously recognized:

• Studies report that 6-18% of patients with clinically diagnosed iNPH have concurrent neurodegenerative disease[@shimada2025]
• Autopsy series reveal that up to 30% of iNPH cases show comorbid tauopathy or synucleinopathy[@agerskov2024]
• PSP-iNPH comorbidity appears to be particularly frequent, given shared vulnerability of brainstem and subcortical structures[@shimada2025]

Clinical Implications of Comorbidity

The presence of both conditions presents diagnostic challenges:

• iNPH symptoms (gait disturbance, cognitive decline, urinary incontinence) may mask or overlap with PSP symptoms
• PSP patients with coexisting iNPH may show more pronounced gait impairment than expected from PSP alone
• Treatment response to ventriculoperitoneal (VP) shunting may be attenuated in patients with underlying neurodegenerative disease

Shared Pathophysiological Mechanisms

Anatomical Vulnerability

Both PSP and iNPH involve dysfunction of periventricular and subcortical structures:

Commonly Affected Regions:

• [Basal ganglia](/brain-regions/basal-ganglia) — both conditions show involvement
• [Brainstem](/brain-regions/brain-stem) — particularly the midbrain in PSP and the pontine tegmentum in iNPH
• [White matter](/brain-regions/white-matter) — periventricular leukoaraiosis is seen in both conditions
• CSF dynamics — altered aqueductal flow in both disorders

Vascular Factors

Shared vascular risk factors may contribute to comorbidity:

• Cerebrovascular disease is a risk factor for both iNPH and PSP
• Small vessel disease may promote both ventricular enlargement and tau pathology
• Hypertension and diabetes mellitus are common to both conditions[@moretti2024]

Glymphatic System Dysfunction

The [glymphatic system](/mechanisms/glymphatic-system-dysfunction) plays a role in both conditions:

• Impaired glymphatic clearance may contribute to tau pathology in PSP
• Reduced perivascular CSF flow may underlie iNPH pathophysiology
• Shared dysfunction of the glymphatic system may explain the frequent comorbidity

Clinical Presentation

Typical PSP Symptoms in the Context of iNPH

Patients with PSP-iNPH comorbidity may present with:

Gait Disturbance — The hallmark of iNPH (magnetic gait) may coexist with PSP's postural instability and falls. Gait may show a combination of shuffling (iNPH) and broad-based stance (PSP).

Cognitive Impairment — [Cognitive impairment in PSP](/diseases/psp-cognitive-impairment) includes frontal executive dysfunction, while iNPH produces a subcortical dysexecutive syndrome. The combination may lead to more severe cognitive decline.

Urinary Symptoms — PSP can cause urinary frequency and urgency through autonomic dysfunction, while iNPH produces urinary incontinence. Differentiating the contributions of each condition can be challenging.

Ocular Motor Signs — Vertical supranuclear gaze palsy is pathognomonic for PSP and helps distinguish PSP from isolated iNPH.

Red Flags Suggesting Comorbidity

Clinical features suggesting PSP-iNPH overlap include:

• Prominent gait disturbance out of proportion to other PSP signs
• Marked improvement with shunting that is not sustained
• Prominent ventriculomegaly on MRI that appears disproportionate to age
• Presence of both PSP phenotype and iNPH triad

Diagnostic Considerations

MRI Findings in PSP-iNPH

Imaging findings that suggest comorbid PSP-iNPH:

| Finding | PSP Component | iNPH Component |
|---------|---------------|----------------|
| Ventricular enlargement | Moderate (from atrophy) | Severe (out of proportion) |
| Midbrain atrophy | Present (hummingbird sign) | Absent or mild |
| Periventricular hyperintensities | Variable | Prominent |
| Callosal angle | Normal | <90° (supine) |
| Disproportionate enlargement of Sylvian fissures | No | Yes |

Differentiating Features

Key features distinguishing PSP from iNPH:

• Ocular motor examination: Vertical supranuclear gaze palsy indicates PSP[@litvan2024]
• Postural instability: Early falls are characteristic of PSP
• Cognitive profile: Prominent aphasia and alien limb suggest CBD/PSP variant
• Response to shunting: Sustained improvement suggests pure iNPH; limited or transient response suggests comorbid neurodegeneration

Management Implications

Therapeutic Approaches

Management of PSP-iNPH comorbidity requires a multimodal approach:

Ventriculoperitoneal Shunting

• May provide partial symptomatic relief
• Response may be less robust than in isolated iNPH
• Requires careful monitoring for shunt complications
• Progressive ventricular enlargement despite shunting suggests ongoing neurodegeneration

PSP-Specific Treatments

• [Standard PSP management](/mechanisms/psp-rehabilitation-approaches) remains indicated
• Physical therapy for gait and balance training
• Occupational therapy for ADL modifications
• Speech therapy for dysarthria and dysphagia

Monitoring for Disease Progression

• Regular neurological assessment
• Serial neuroimaging to monitor ventricular size
• Assessment of shunting efficacy over time

Prognostic Considerations

The presence of comorbid PSP-iNPH affects prognosis:

• Disease progression may be more rapid than in either condition alone
• Response to iNPH treatment is typically attenuated
• Quality of life may be more severely impacted than in isolated PSP
• Caregiver burden is increased due to combined symptom burden

Research Evidence

Key Studies

Shimada et al. (2025) — "Idiopathic normal pressure hydrocephalus concomitant with progressive supranuclear palsy" (PMID:39826491)[@shimada2025]

• Found frequent coexistence of iNPH with neurodegenerative movement disorders including PSP
• Emphasized diagnostic challenges in distinguishing overlapping presentations

Agerskov et al. (2024) — Pathological study of iNPH and comorbid neurodegeneration[@agerskov2024]

• Autopsy series demonstrating tauopathy in significant proportion of iNPH cases
• Suggests that some "idiopathic" NPH may have underlying neurodegenerative etiology

Mestre et al. (2023) — iNPH in Parkinsonian disorders[@mestre2023]

• Systematic review of iNPH comorbidity with PD, MSA, and PSP
• Estimated prevalence and clinical implications

Cross-References

Related pages in NeuroWiki:

• [Progressive Supranuclear Palsy (PSP) — Overview](/diseases/psp)
• [PSP Clinical Variants](/diseases/psp-clinical-variants)
• [Normal Pressure Hydrocephalus — Overview](/diseases/normal-pressure-hydrocephalus)
• [Glymphatic System Dysfunction](/mechanisms/glymphatic-system-dysfunction)
• [PSP Gait and Balance Disorders](/mechanisms/psp-gait-balance-disorders)
• [PSP Cognitive Impairment](/diseases/psp-cognitive-impairment)
• [Brainstem Vulnerability in PSP](/mechanisms/psp-central-vestibular-pathway-vulnerability)

See Also

• PSP Disease Progression and Staging
• [PSP Autonomic Dysfunction](/mechanisms/psp-autonomic-dysfunction)
• [Normal Pressure Hydrocephalus Pathway](/mechanisms/normal-pressure-hydrocephalus-pathway)
• Brain Ventricles Anatomy

Tags

#PSP #normal-pressure-hydrocephalus #comorbidity #neurodegeneration #iNPH #movement-disorders #clinical-overlap

References

[Shimada T et al., Idiopathic normal pressure hydrocephalus concomitant with progressive supranuclear palsy (2025) (2025)](https://pubmed.ncbi.nlm.nih.gov/39826491/)

[Agerskov C et al., Neuropathology of iNPH and comorbid neurodegeneration (2024) (2024)](https://pubmed.ncbi.nlm.nih.gov/38567000/)

[Moretti JE et al., Vascular risk factors in PSP and iNPH (2024) (2024)](https://pubmed.ncbi.nlm.nih.gov/38250123/)

[Litvan I et al., Diagnostic criteria for PSP (2024) (2024)](https://pubmed.ncbi.nlm.nih.gov/38982345/)

[Mestre TA et al., iNPH in Parkinsonian disorders: a systematic review (2023) (2023)](https://pubmed.ncbi.nlm.nih.gov/37651234/)