Normal pressure hydrocephalus (NPH) occurs in the elderly and is a progressive cognitive deterioration, gait apraxia/imbalance, and urinary incontinence associated with hydrocephalus with normal cerebrospinal fluid (CSF) pressure on lumbar puncture. It is thought of as a treatable dementia, the symptom most likely to appear first and to improve after shunt surgery is gait impairment. Patients do not need to have the complete triad of symptoms to have NPH. It can be secondary to processes such as subarachnoid hemorrhage, traumatic brain injury, or meningitis, although one half of patients will have an idiopathic cause. NPH results from a disruption in the CSF circulation leading to gradual enlargement of the ventricles and emergence of symptoms. In large series 1-1.6% of dementia was attributed to NPH. Due to a low incidence other causes of the patients symptoms should be excluded such as vascular/degenerative dementia, spinal stenosis, neuropathy, arthritis, bladder instability, and prostate enlargement. Diagnosis with neuroimaging is difficult secondary to elderly patients ventricles appearing enlarged either because of hydrocephalus or cerebral atrophy (ie degenerative dementia or subcortical ischemia). All patients with a negative work up and suspected NPH should have a non-emergent referral to neurosurgery. Clinical response to CSF removal through lumbar puncture or continuous CSF drainage is likely the most accurate method for diagnosing NPH. Treatment is placement of a shunt. The size of the ventricles observed on imaging studies is an unreliable indicator of recovery or as an indicator for recurrence of symptoms. The most common complication associated with shunts in NPH is obstruction, which occurs in up to 1/3rd of patients. Less common shunt complications include subdural hematomas or hygromas.
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