Pupillary Changes in Normal Pressure Hydrocephalus
Pupillary constriction is not a characteristic feature of Normal Pressure Hydrocephalus (NPH). NPH presents with a classic clinical triad of gait disturbance, cognitive impairment, and urinary incontinence—pupillary abnormalities are not part of this syndrome 1, 2, 3.
Why Pupillary Changes Are Not Expected in NPH
Normal intracranial pressure is the defining feature: NPH is characterized by normal or only mildly elevated mean basal intracranial pressure, which distinguishes it from conditions that cause pupillary changes through increased ICP 4, 5.
Visual symptoms are uncommon: Given that intracranial pressure typically remains normal in NPH, visual symptoms and pupillary abnormalities are quite rare in this condition 5.
No brainstem compression: Unlike conditions with mass effect or acute hydrocephalus, NPH does not typically cause brainstem compression that would lead to pupillary dysfunction 1.
When Pupillary Changes DO Occur in Hydrocephalus
It's critical to distinguish NPH from other forms of hydrocephalus where pupillary changes are expected:
Acute obstructive hydrocephalus: In cerebellar infarcts with acute hydrocephalus and brainstem compression, patients develop pupillary anisocoria, pinpoint pupils, and loss of oculocephalic responses 1.
Increased ICP from any cause: Pupillary abnormalities (including midposition pupils or unilateral dilation) are late signs of increased intracranial pressure and impending herniation 1.
Progressive deterioration: Gradual development of midposition pupils with worsening motor response indicates rising ICP and deterioration—this is NOT the typical presentation of NPH 1.
Clinical Pitfall to Avoid
If a patient presents with what appears to be NPH symptoms (gait disturbance, cognitive impairment, incontinence) plus pupillary abnormalities, consider alternative diagnoses:
- Acute obstructive hydrocephalus requiring emergency intervention 1
- Mass lesion with increased ICP 1
- Comorbid neurodegenerative disease (present in 20-57% of NPH patients) with additional pathology 3, 6
- Secondary NPH from trauma, hemorrhage, or meningitis with complications 1
The presence of pupillary changes should prompt urgent neuroimaging and consideration of neurosurgical consultation, as this suggests a more acute process than typical NPH 1.