Numerous tests have been assessed to predict those most likely to benefit from operation. The most reliable are -
Other tests include the presence of periventricular lucency or disproportionate sulcal width on CT scan, isotope cisternography and CSF infusion studies but none appear to produce a reliable guide.
Operation: Ventriculo-peritoneal shunting (see page 363).
Results: Improvement occurs in 50-70% of those patients with a known preceding cause e.g. subarachnoid haemorrhage. Only 30% of the idiopathic group respond to shunting.
Reduction of intellectual function is common after severe head injury. Chronic subdural haematoma can also present as progressive dementia, especially in the elderly. Punch-drunk encephalopathy (dementia pugilistica) is the cumulative result of repeated cerebral trauma. It occurs in both amateur and professional boxers and is manifest by dysarthria, ataxia and extrapyramidal signs associated with 'subcortical' dementia. There is no treatment for this progressive syndrome.
Concern is always expressed at the possibility of dementia being due to intracranial tumour. This is rare, but may happen when tumours occur in certain sites.
Mental or behavioural changes occur in 50-70% of all brain tumours as distinct from dementia which is associated with frontal lobe tumours (and subfrontal tumours), III ventricle tumours and corpus callosum tumours.
(i) The presence of beta waves on continuo intracranial pressure monitoring for more than 5% of a 24 hour period.
(ii) Clinical improvement with continuous lumbar CSF drainage of 200 ml per day for three to five days.
Beta waves i_i
N.B. Dementia can occur as a symptom of a more widespread degenerative disorder
Cognitive impairment also occurs as a non metastatic complication of systemic malignancy.
Suspect in recent onset dementia with focal signs, e.g. subfrontal lesions may be associated with loss of smell (I cranial nerve involvement) and optic atrophy (II cranial nerve involvement).
e.g. Parkinson's disease
Diffuse Lewy body disease Progressive supranuclear palsy
Huntington's disease Motor neurone disease
These will be considered later
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