What is normal pressure hydrocephalus? Normal pressure hydrocephalus is a rare condition in which a patient has symptoms of hydrocephalus but a lumbar puncture shows normal cerebrospinal fluid pressure. However, there is evidence that cerebrospinal fluid pressure is not always normal. Some scholars refer to it more appropriately as “chronic hydrocephalus”. What are the signs of normal pressure hydrocephalus? The typical clinical manifestations are a triad of gait abnormalities, dementia, and urinary incontinence. Gait abnormalities are non-specific and may resemble Parkinson’s disease; the gait is unsteady and sloppy. Patients often have difficulty in starting, as if their feet are glued to the floor (so also
called “magnetic
gait”), have difficulty turning or going around obstacles, and need to take more steps. Unlike Parkinson’s disease, however, the gait base is normal or widened and the arms swing when walking. Patients have subcortical mental impairment, including inattention, amnesia, and slowness to receive information; there is no aphasia, dysarthria, or anosognosia. Urinary incontinence and even fecal incontinence occur only when the disease progresses to an advanced stage. What is the pathophysiological basis of normal pressure hydrocephalus? The cause of normal pressure hydrocephalus is unknown in about half of the patients and is therefore called idiopathic normal pressure hydrocephalus. The remaining causes are subarachnoid hemorrhage, meningitis, and cranial trauma or surgery – all factors that can alter cerebrospinal fluid dynamics. Imbalance in cerebrospinal fluid production and absorption leads to ventricular enlargement. Although a lumbar puncture shows normal cerebrospinal fluid pressure, intracranial cerebrospinal fluid pressure does not necessarily do so. Factors that can contribute to ventricular enlargement include increased cerebrospinal fluid pulse pressure, pressure step differences between the ventricles and the subarachnoid space, and expandable enlargement of the ventricles. The enlargement of the anterior foot of the ventricle pulls on the sacral motor nerve fibers, affecting the innervation of the lower extremities and sphincter muscles, leading to gait abnormalities and urinary incontinence. The periventricular arteries and veins of the enlarged ventricle are stretched and squeezed so that the microcirculation around the limbic system is affected, leading to impaired cognitive function. Can normal pressure hydrocephalus be effectively treated? Medications There is no effective medication for normal pressure hydrocephalus . Cases treated with levodopa or carbidopa are more likely to be Parkinson’s disease that has been misdiagnosed as such. Surgery Surgical shunting of cerebrospinal fluid (e.g., ventriculoperitoneal shunt) is the only proven effective treatment, but it is only effective in some patients. Improvement in patient gait and cognitive function after massive cerebrospinal fluid aspiration (30-50 ml) is a criterion to determine that a patient can benefit from surgery. Normal pressure hydrocephalus has a poor prognosis. Surgical treatment may result in substantial improvement in 30-50% of patients with idiopathic and 50-70% of patients with secondary normal pressure hydrocephalus. The incidence of severe surgical comorbidities (including severe neurological deficits and death) can be as high as 5-8%. The incidence of milder comorbidities ranges from 20 to 40%. Patients with normal pressure hydrocephalus should be referred to neurology and neurosurgery for further consultation.