MIDWAY:No going back

The confirmation last week that Baroness Thatcher suffers from dementia is only really surprising in its particulars — but they are moving particulars, nonetheless.

The woman who, as her daughter Carol writes in her new memoir, A Swim-On Part in the Goldfish Bowl, “had a memory like a website”, and was capable, during Prime Minister’s Questions, of “not only reading and analysing briefs but also virtually knowing them off by heart,” now often forgets the beginning of sentence by the time she has got to the end.

She also thinks her home is in Grantham (her birthplace in Lincolnshire) when it is in London, and has had to be told that her husband Denis is dead long time back. Thatcher’s trouble seems not to be linked to Alzheimer’s, but to the degenerative effect of a series of frequent small strokes (which can cause vascular dementia, in which the blood supply to the brain is affected).

There are more than 100 types of dementia, the symptoms of which include mood changes, forgetfulness and communication problems; dementia could be described as a symptom in itself, as it is usually brought about by other diseases, from Aids to multiple sclerosis, CJD to Parkinson’s disease, Down’s syndrome to high blood pressure and diabetes. It affects about 700,000 Britons; that number is expected to rise to a million by 2026.

According to the Alzheimer’s Society, one in 50 people between the ages of 65 and 70 has a form of dementia, compared with one in five people over the age of 80 — Thatcher is 82. (Although Niemann-Pick, a rare disease, means children can develop it too).

Women over 90 are much more likely to suffer dementia than men of the same age, and women are slightly more likely to develop Alzheimer’s than men.

Better-educated people seem to be less likely to develop dementia than less-educated people, but, as Thatcher has discovered, not even being leader of your country for 11 years guarantees safety.

And the lady who was never keen on turning probably already knows that while it is possible

to slow the progress of dementia, there is no way to reverse the damage once it has been done.