Normal pressure hydrocephalus (NPH), also called malresorptive hydrocephalus, is a form of communicating hydrocephalus in which excess cerebrospinal fluid (CSF) builds up in the ventricles, leading to normal or slightly elevated cerebrospinal fluid pressure. The fluid build-up causes the ventricles to enlarge and the pressure inside the head to increase, compressing surrounding brain tissue and leading to neurological complications. Although the cause of idiopathic (also referred to as primary) NPH remains unclear, it has been associated with various co-morbidities including hypertension, diabetes mellitus, Alzheimer's disease, and hyperlipidemia. Causes of secondary NPH include trauma, hemorrhage, or infection. The disease presents in a classic triad of symptoms, which are memory impairment, urinary frequency, and balance problems/gait deviations (note: use of this triad as the diagnostic method is obsolete; the triad symptoms appear at a relatively late stage, and each of the three can be caused by a number of other conditions). The disease was first described by Salomón Hakim and Raymond Adams in 1965. The usual treatment is surgical placement of a ventriculoperitoneal shunt to drain excess CSF into the lining of the abdomen where the CSF will eventually be absorbed. An alternate, less invasive treatment is endoscopic third ventriculostomy. NPH is often misdiagnosed as other conditions including Meniere's disease (due to balance problems), Parkinson's disease (due to gait) or Alzheimer's disease (due to cognitive dysfunction).
Signs and symptoms NPH exhibits a classic triad of clinical findings (known as the Adams triad or Hakim's triad). The triad consists of walking difficulty, reduced attention span, and urinary frequency or incontinence. Symptoms present insidiously over the course of 3–6 months. The triad is considered obsolete for diagnostic purposes and newer guidelines are available. Gait deviations/balance problems are present in nearly all NPH patients and are typically the first presenting symptom. This is caused by expansion of the lateral ventricles, which can impinge on the corticospinal tract motor fibers. The typical gait abnormality in NPH is a broad-based, slow, short-stepped, "stuck to the floor", or "magnetic" movement. The gait abnormalities in NPH may bear resemblance to a gait associated with Parkinson's disease. The gait deviation can be classified as mild, marked, or severe: "marked" is when the patient has difficulty walking because of considerable instability; "severe" is when it is not possible for the patient to walk without aids (such as a cane or a wheeled walker). An associated tremor of the hands, legs, or feet can be seen in up to 40% of NPH patients. Dementia presents as progressive cognitive impairment which is present in 60% of patients at time of treatment. This is caused by distortions predominantly at the frontal lobe and the subcortex. Initial deficits involve planning, organization, attention, and concentration. Further deficits include difficulty managing finances, taking medications, driving, keeping track of appointments, daytime sleeping, short-term memory impairments, and psychomotor slowing. Late-stage features include apathy, reduced drive, slowed thinking, and reduced speech. Urinary incontinence appears late in the illness and is present in 50% of patients at time of treatment. Urinary dysfunction begins as increased frequency often at night and progresses to urge incontinence and permanent incontinence.
Pathogenesis Every day, the body makes roughly 600–700 ml of CSF, and about the same amount is reabsorbed into the bloodstream. Hydrocephalus is caused by an imbalance between the amount of fluid produced and its absorption rate. Enlarged ventricles put increased pressure on the adjacent cortical tissue and cause myriad effects in the patient, including distortion of the fibers in the corona radiata. This leads to an increase in intracranial pressure (ICP). The ICP gradually falls but remains slightly elevated, and the CSF pressure reaches a high normal level of 15 to 20 cm H2O. Measurements of ICP, therefore, are not usually elevated. Because of this, patients do not exhibit the classic signs that accompany increased intracranial pressure such as headache, nausea, vomiting, or altered consciousness, although some studies have shown pressure elevations to occur intermittently. The exact pathogenesis is unknown, but consensus on some mechanisms include:
An imbalance exists between production and resorption of CSF. The resistance to CSF outflow is often elevated. The disease is not caused by overproduction of CSF or obstruction of CSF flow at the ventricles. The syndrome is often divided into two groups, primary (also called idiopathic) and secondary, based on cause. The underlying etiology of primary NPH has not yet been identified. Primary NPH affects adults age 40 years or older, most commonly in adults over 60. Secondary NPH can affect persons of any age and occurs due to conditions such as subarachnoid hemorrhage, meningitis, brain surgery, brain radiation, or traumatic brain injury. These conditions are thought to lead to increased inflammation of the arachnoid granulations, which further leads to decreased CSF reabsorption and therefore enlargement of ventricles. Symptoms of gait deviation, neurological impairment, and urinary incontinence seen in NPH are due to compression of the corresponding regions of the brain that control these functions. Gait abnormalities are thought to be due to compression of the corticospinal tract fibers in the corona radiata that coordinate motor movements of the legs. Compression of the brainstem as well as poor perfusion of the periventricular white matter in the prefrontal cortex are also thought to contribute to gait deviations in NPH. Dementia in NPH is most likely caused by ventricular enlargement compressing the calvarium, which further leads to tearing of currently unidentified nerve fibers. Lastly, urinary incontinence is thought to be caused by stretching of the periventricular sacral fibers of the corticospinal tract fibers leading to loss of voluntary bladder contraction.
Diagnosis
… excerpt ends here. Continue reading the full article.
