Normal pressure hydrocephalus (NPH) is a neurodegenerative disorder characterized by the triad of dementia, progressive gait abnormalities, and urinary urgency or incontinence.
- Most common form of hydrocephalus in adults
- Incidence: 2–20 cases per million individuals per year
- Prevalence increases with age, usually > 60 years:
- 0.2% in individuals ages 70–79
- 6% in individuals > age 80
- Represents approximately 6% of all cases of dementia
- No sex predilection
- Idiopathic: due to a combination of mechanisms
- Secondary causes:
- Most common: intraventricular and subarachnoid hemorrhage
- Acute or chronic meningitis
- Traumatic brain injury (TBI)
- Paget disease (rare)
The pathophysiology of NPH is still unclear.
- Possible contributing mechanisms:
- Subclinical congenital hydrocephalus
- Hyperdynamic flow of CSF
- Reduced compliance of the subarachnoid space
- Decreased reabsorption of CSF
- Reduced cerebral blood flow
- Increased central venous pressure
- Accumulation of CSF in the cranial vault
- Increased intracranial pressure (ICP) → compression of corticospinal tract fibers (close to the lateral ventricles) and brain stem (pedunculopontine nucleus) → gait abnormalities
- Enlargement of ventricles → poor interstitial perfusion and ischemia → pushing of cerebral cortex against the bones of the calvarium → dementia
- Compression of periventricular sacral fibers of the corticospinal tract → loss of supraspinal control of bladder contraction → urinary incontinence
Clinical Presentation and Diagnosis
Family members or caretakers may report personality and/or behavioral changes and frequent urination or incontinence.
- Classic triad of symptoms:
- Progressive gait abnormalities
- Urinary urgency and/or incontinence
- “Wet, wacky, and wobbly” = incontinence, dementia, and gait dysfunction
- “AID” = ataxia, incontinence, and dementia
- Gait abnormalities:
- 1st and most common symptom
- Shuffling or wide-based gait
- External rotation of feet
- Multiple-step turns
- Freezing of gait
- Executive dysfunction
- Complex processes that require integration of complex, goal-oriented tasks and behaviors
- Poor judgment
- Socially inappropriate behavior
- Psychomotor retardation
- Reduced attention and concentration
- Executive dysfunction
- Urinary urgency and/or incontinence:
- Gait abnormality may interfere with getting to the bathroom with urgency.
- Later stages → lack concern about incontinence
- Symptoms not found with NPH that are seen with increased ICP:
- Nausea and vomiting
- Visual loss
- History and physical exam:
- Not all 3 features are required for diagnosis; need gait dysfunction plus ≥ 1 of the other 2
- Cognitive evaluation with Mini–Mental State Examination
- Possible medication side effects
- Lab testing—rule out treatable causes of dementia:
- Vitamin B12 level
- Thyroid function tests
- Large volume lumbar puncture (LP; tap test):
- Document gait function before LP:
- Gait speed
- Stride length
- Number of steps it takes to turn 360 degrees
- Videotape may be helpful to compare with function after LP.
- Normal opening pressure (6–20 cm H2O) is seen with NPH.
- Remove 30–50 mL of CSF.
- Documented improvement in gait function 30–60 minutes after procedure suggests improved outcome after ventriculoperitoneal (VP) shunt.
- Document gait function before LP:
- X-ray: Consider cervical or lumbar spinal X-rays to evaluate for spondylosis causing gait dysfunction.
- MRI of the brain:
- Characteristic high signal periventricular white matter changes
- Enlarged subarachnoid space
- Sylvian fissure widening
- CSF flow rate > 24.5 mL/min is 95% specific for NPH.
Management and Prognosis
The treatment of NPH is with an implanted ventricular shunt.
- Types of shunts:
- Ventriculoperitoneal (VP): surgically created communication between the lateral ventricle and the peritoneal cavity
- Ventriculoatrial: catheter from the lateral ventricle into the heart
- Predictors of improvement with shunts:
- Early appearance of gait disorder
- Gait disorder most prominent symptom
- Duration of symptoms < 6 months
- Clinical response to CSF removal by LP
- Absence of negative prognostic indicators:
- Early appearance of dementia
- Dementia for > 2 years
- Complications of shunts:
- Most common complication in 1st year
- May be asymptomatic or may present with headaches
- Radiologic signs: subdural effusions; subdural hematoma due to tearing of the bridging veins
- Intracerebral hemorrhage during catheter placement in 3%–6% of cases
- Blocked shunt
- Arrhythmias during catheter placement in ventriculoatrial shunts
- Individuals have an 80%–90% chance of improvement in all symptoms after surgery.
- Worse outcomes are seen with:
- Severe dementia or dementia as the presenting symptom
- Concomitant cerebrovascular disease
- Cerebral atrophy and multiple white matter lesions on MRI
- Delayed recognition
- Alzheimer disease: progressive neurodegenerative disease that causes brain atrophy and presents with a decline in memory, cognition, and social skills. Several genetic defects and risk factors have been described for Alzheimer disease, but there is no clear cause in the majority of cases. Diagnosis is based on clinical examination, neuropsychiatric testing, and imaging. There is no curative therapy, but symptomatic management with medications, including cholinesterase inhibitors and others, may slow the progression.
- Dementia with Lewy bodies (DLB): Lewy bodies are thought to be responsible for impaired mental functions related to thinking, movement, behavior, and mood in DLB. The presence of Lewy bodies alters the level of neurotransmitters and neuromodulators in the brain, principally dopamine. Diagnosis is based on clinical symptoms and MRI. Management is symptomatic for specific manifestations of the disease.
- Frontotemporal dementia: neurodegenerative disorder characterized by loss of cognitive functions (memory, abstract thinking, reasoning, and executive function) that severely impairs functioning and quality of life. Clinical presentation includes behavioral changes, such as apathy. Diagnosis is based on interviewing caregivers/family members and imaging to rule out other pathology. Management is both pharmacologic and nonpharmacologic to lessen symptoms.
- Parkinson’s disease: chronic, progressive neurodegenerative disorder. Although the cause of Parkinson’s disease is unknown, there are several genetic and environmental risk factors that are currently being studied. Individuals present clinically with resting tremor, bradykinesia, rigidity, and postural instability. Diagnosis is clinical. Treatment includes supportive physical and emotional care plus medications such as levodopa/carbidopa, monoamine oxidase type B inhibitors, and dopamine agonists.
- Atypical parkinsonian syndromes: progressive supranuclear palsy (PSP) and corticobasal degeneration (CBD) are neurodegenerative disorders characterized by their display of parkinsonian features but with different pathophysiology. Both PSP and CBD have cognitive manifestations and motor symptoms. Diagnosis is clinical and with MRI. Management is supportive and with levodopa/carbidopa for PSP, but does not reduce symptoms in CBD. Other medications may help with tremors, myoclonus, and cognitive dysfunction.
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- Berkowitz, A.L. (2016). Delirium, dementia, and rapidly progressive dementia. Chapter 22 of Clinical Neurology and Neuroanatomy: A Localization-based Approach. McGraw-Hill Education. http://accessmedicine.mhmedical.com/content.aspx?aid=1160205112
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- Williams, M.A., Malm, J. (2016). Diagnosis and treatment of idiopathic normal pressure hydrocephalus. Continuum 22:579–599. DOI: 10.1212/CON.0000000000000305