Normal pressure hydrocephalus refers to a condition of pathologically enlarged ventricular size with normal opening pressures on lumbar puncture. It is a form of communicating hydrocephalus .Because this clinical syndrome is potentially reversible it is important for healthcare professional to recognize it timely and treat acoordingly .
ETIOLOGY
Mostly cause is unknown and can arise in the setting of -
Decompensated Congenital Hydrocephalus
Cerebrovascular Disease like hypertension, stroke
Decreased CSF Absorption
Increased Central Venous Pressure
Neurodegenerative Disorders such as Alzheimer Disease (Ad)
However most common cause remains NPH secondary to Impaired absorption of CSF .
The most common causes are intraventricular or subarachnoid haemorrhage and prior acute or ongoing chronic meningitis (from infection, cancer, or inflammatory disease). Paget disease at the skull base, mucopolysaccharidosis of the meninges, and achondroplasia are other rare causes.
These conditions cause inflammation and subsequent fibrosis at the base of the brain and/or the arachnoid granulations, and thereby impair CSF resorption.
CLINICAL FEATURES
1. Gait Difficulty- Described as a magnetic or "glue-footed" gait. Patients move slowly and take small steps with a wide base. They have difficulty turning.
2. Urinary Incontinence- Urinary urgency rather than incontinence may be present at early stages.
3. Cognitive Disturbance- can include Psychomotor slowing, Decreased attention and concentration, Impaired executive function.
Patients need not have all three cardinal features, but gait must be the predominant problem.
NEGATIVE FEATURES
By definition, patients with NPH have a normal opening pressure at the lumbar cistern. The clinical presentation is therefore notable for an absence of signs and symptoms related to diffusely increased intracranial pressure (ICP), such as:
●Headaches
●Nausea and vomiting
●Visual loss
●Papilledema
●Elevated opening pressure (>25 cm water)
DIAGNOSIS AND ASSESSMENT
Multi-Disciplinary Approach used which includes:
• Cognitive evaluation —
• Treatable conditions are excluded. includes a brief cognitive assessment and laboratory evaluations (vitamin B12 level and thyroid function tests).
• In addition neuropsychological testing can be useful for providing a baseline measurement for future comparison .
• Alternative causes of gait and urinary dysfunction should be ruled out.
• Magnetic resonance imaging — MRI is superior to CT . The hallmark finding of NPH on CT or MRI is ventriculomegaly with or without sulcal enlargement, with no evidence of obstruction, with periventricular white matter changes and aqueduct flow void .
Prominent cortical atrophy, argues against the diagnosis of NPH .
CONFIRMATORY TESTS
High-volume lumbar puncture — The simplest test can be done as an office procedure. Using lumbar puncture, 30 to 50 mL of CSF is removed with documentation of the patient's gait function before and within 30 to 60 minutes after the procedure.
Lumbar drain trial
Cisternography — Isotope cisternography consists of injection of a radiolabeled isotope into the lumbar cistern and visualizing its distribution through the cisterns, ventricles, and brain convexities .NPH is suggested by nonappearance of the isotope over the brain convexities at 72 hours.
TREATMENT
A ventricular shunt that controlls CSF flow via a one-way valve in the shunt is the mainstay of treatment.
Ventricular shunting works well in patients with typical clinical features and positive imaging findings for NPH and a positive clinical response to a lumbar tap test or lumbar drain trial.
