Alzheimer’s Dementia:

This is the commonest cause of dementia, seen in about 70% of all cases of dementia in USA. It is more commonly seen in women. Earlier, it was differentiated into two forms: a presenile form and a senile
form. Autopsy shows macroscopic changes such as enlarged cerebral ventricles, widened cerebral sulci and shrinkage of cerebral cortex.

Neurochemically, there is a marked decrease in brain choline acetyltransferase (in other words, CAT) with a similar decrease in brain acetylcholinesterase (AchE).

Treatment:

Cholinesterase Inhibitors:

•    Rivastigmine(1.5 mg twice a day to 6 mg twice a day).
•    Donepezil(5-10 mg/day).
•    Galantamine (4 mg twice a day to 12 mg twice a day) have used in the recent past for treatment of moderate dementia with Alzheimer’s disease.

These elevate acetylcholine (Ach) concentrations in cerebral cortex by slowing the degradation of acetylcholine released by still intact cholinergic neurons in Alzheimer’s disease.
Memantine (5-20 mg/day), an N-methyl-D’Aspartate (NMDA) antagonist, is also available for the treatment of moderately severe to severe Alzheimer’s disease.

2. Multi-infarct Dementia:

Multi-infarct dementia is the second commonest cause of dementia, seen in 10-15% of all cases, though it is probably more common in India. Occurrence of multiple cerebral infarctions can lead to a progressive disruption of brain function, leading to dementia.
The most typical form of multi-infarct dementia is characterised by the following features:
1. An abrupt onset.
2. Acute exacerbations (due to repeated infarct ions).
3. Stepwise clinical deterioration (especially, step-ladder pattern).
4. Fluctuating course.
5. Presence of hypertension (most commonly) or any other significant cardiovascular disease.
6. History of previous stroke or transient ischemic attacks (in other words, TIAs).

Diagnosis: Emotional lability is common. EEG (specifically, showing focal area of slowing) and brain imaging (either CT scan or MRI scan of brain showing multiple infarcts) help in diagnosis.

3. Hypothyroid Dementia

This has been considered one of the most important treatable also reversible causes of dementia, second only to toxic dementias.

Although it accounts for less than 1% of dementias, hypothyroidism should be suspected in every patient of dementia.

All in all, Prompt treatment can reverse the dementing process and can lead to complete recovery if the treatment is start within two years of the onset of dementia.

4. AIDS Dementia

Complex:

About 50-70% of patients suffering from AIDS exhibit a triad of cognitive, behavioural and motoric deficits of subcortical dementia type and this is known as the AIDS-dementia complex (in other words, ADC).

As the AIDS virus (a lentivirus, a type of retrovirus) is highly neurotropic and the virus crosses the blood-brain barrier early in the course of the disease cognitive impairment is nearly ubiquitous in AIDS.
Diagnosis: The diagnosis is established by ELISA (enzyme linked immunosorbent assay) showing anti-HIV antibodies, and the Western Blot test (blotting of antibody specificities to HIV-specific proteins).

A Cranial CT scan can show cortical atrophy 1-4 months before the onset of clinical dementia while MRI scan is helpful in detecting the white matter lesions.

5. Lewy Body Dementia

Lewy body dementia is now believe to be the second most common cause of the degenerative dementias, accounting for about 4% of all dementias.

Typically, the clinical features of Lewy body dementia include:

i. Fluctuating cognitive impairment over weeks or months, with involvement of memory and higher cortical functions (such as language, visuo-spatial ability, praxis and reasoning). Lucid intervals can be present in between fl uctuations.
ii. Recurrent and detailed visual hallucinations.
iii. Spontaneous extrapyramidal or parkinsonian symptoms such as rigidity and tremors.
iv. Neuroleptic sensitivity syndrome, characterised by a marked sensitivity to the effects of typical doses of antipsychotic drugs (resulting in severe extrapyramidal side-effects with use of antipsychotics).

Other clinical features:

It may include repeated falls, autonomic dysfunction (e.g. orthostatic hypotension), urinary incontinence, delusions and depressive features.

Although Lewy bodies (intracytoplasmic inclusion bodies) are also present in Parkinson’s disease, the occurrence of Lewy bodies in Lewy body dementia is more widespread. Antipsychotic medication should be avoided (or used with extreme caution and in low doses) in patients with Lewy body dementia.

Diagnosis: A PET (Positron Emission Tomography) or SPECT (Single Photon Emission Computerised Tomography) scan of brain may show low dopamine transporter uptake in basal ganglia.