Dementias Specific Diseases

NORMAL PRESSURE HYDROCEPHALUS

Normal pressure hydrocephalus (NPH) is the term applied to the triad of:

Dementia

Gait disturbance

Urinary incontinence occurring in conjunction with hydrocephalus and normal CSF pressure.

Two types occur:

- NPH with a preceding cause - subarachnoid haemorrhage

- meningitis

- trauma

- radiation-induced

(This must be distinguished from hydrocephalus with raised intracranial pressure associated with these causes.)

- NPH with no known preceding cause - idiopathic (50%).

Aetiology is unclear. It is presumed that at some preceding period, impedence to normal CSF flow causes raised intraventricular pressure and ventricular dilatation. Compensatory mechanisms permit a reduction in CSF pressure yet the ventricular dilatation persists and causes symptoms:

Pressure on frontal lobes (possibly related to decreased cerebral blood flow).

—• Pressure on the cortical centre for bladder and bowel control in the paracentral lobe. Pressure on the 'leg fibres' from the cortex passing around the

-Dementia

• Incontinence

Gait disturbance and pyramidal ventricle towards the internal capsule. signs in the legs

Diagnosis is based on clinical picture plus CT scan/MRI evidence of ventricular enlargement.

The lateral ventricles are often dilated more than the 3rd and 4th

The lateral ventricles are often dilated more than the 3rd and 4th

Note the presence or absence of periventricular lucency (PVL) and width of cortical sulci

Normal pressure hydrocephalus must be differentiated from patients whose ventricular enlargement is merely the result of shrinkage of the surrounding brain, e.g. Alzheimer's disease. These patients do not respond to CSF shunting, whereas a proportion of patients with NPH (but not all) show a definitive improvement with shunting.

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