Although Alzheimer's disease is the commonest and the best-known type of dementia, there are several other types that occur in old age. Recently, a form known as Lewy body dementia is being recognized more often; it is now considered to be responsible for 15% to 25% of new cases of dementia in the elderly. It gets its name from microscopic collections of abnormal proteins stored within nerve cells, forming what are called Lewy bodies. These bodies represent remains of destroyed nerve cells. Different symptoms predominate, depending on where the Lewy bodies occur in the brain. Often they are situated in the striatum, producing symptoms resembling Parkinson's disease (i.e. parkinsonism). If they occur in the cerebral cortex, there is mental disability and sometimes more severe mental illness (psychosis).

Dementia with Lewy bodies (DLB) usually causes delirium, confusion, lack of attention, parkinsonism, and hallucinations. Occasionally fainting and falling occur.

Its important to be able to diagnose DLB, because the condition improves when certain types of drugs called cholinesterase inhibitors are given (e.g. tacrine, rivastigmine). On the other hand, if patients with DLB are given neuroleptic drugs, such as thioridazine, they react badly, and their parkinsonism gets worse.

A new study done in UK, Spain and Italy, has examined the safety and effectiveness of the cholinesterase inhibitor, rivastigmine, in 120 patients with DLB. The subjects were divided into two groups, one given rivastigmine and the other placebo (i.e. matching dummy tablets), twice daily for 20 weeks, followed by a 3-week off-medication period. The rivastigmine doses started at 1.5 mg twice a day and could be increased up to a 6 mg twice a day.

At baseline, and then at weeks 12, 20 and after 3 weeks off-medication, a battery of neuropsychiatric questions were answered by the subjects caregiver, and computerized response-speed testing was done. The neuropsychiatric tests assessed delusions, hallucinations, apathy and depression. The computerized speed tests measured attention, working memory and episodic memory.

Over half the subjects were men (55%), and the average age was 74. Fewer participants completed the 20 weeks period on rivastigmine than on placebo (41 vs. 51). Failure-to-complete was due to various causes, but none were related to toxicity of rivastigmine. The final daily doses of rivastigmine lay between 6 and 12 mg.

While subjects in both groups improved their neuropsychiatric scores during the 20-week medication period, the improvement with rivastigmine was significantly better than with placebo. The elements that improved most with rivastigmine were apathy, indifference, anxiety, delusions, hallucinations, and abnormal movements.

The computerized speed tests showed that subjects taking rivastigmine were significantly faster in their reactions, particularly in tasks focusing on attention.

At the end of the 3-week off-medication period, the participants on rivastigmine had scores that showed the beneficial effects of the drug were wearing off.

Side effects were reported by most of the participants, but those often seen with cholinesterase inhibitor drugs were more prominent in the rivastigmine subjects. These were nausea, vomiting, loss of appetite and drowsiness. Three of the subjects on rivastigmine had moderate to severe agitation as a side effect. There were no effects of medications on lab tests, vital signs or ECG results.

Although the scientists expected rivastigmine to be helpful for these patients, it was important that they were able to demonstrate this using neuropsychiatric symptom lists prepared with the help of the caregiver, as well as computerized reaction-speed tests. This showed that these tests can be used for testing treatments in people with dementia, and may, indeed, be more relevant than the usual scales used today.

Another important outcome is realization that a lack of choline is found in Parkinson's disease patients who have dementia, and in people who have mixed Alzheimer's and vascular dementia. It is logical to think that this type of drug would be useful in these patients, too. Up to now, physicians have been worried about using cholinesterase inhibitors in people with parkinsonism, for fear of making things worse. However, as over 90% of the subjects in this study had some degree of parkinsonism at the start of the study, and didnt get worse on rivastigmine, it is probably safe to use this type of drug in other types of dementia, even if parkinsonism is present.