THE BEVERLY ALLITT case has catapulted the phrase Munchhausen syndrome by proxy out of the medical dictionaries and into the headlines. But we are no wiser as to why sufferers do such awful things. However, Hurting for Love, a book published in America last month, not only provides a convincing explanation, but suggests that the syndrome is much more common than the experts believed.

The one figure who has been missing from all accounts of this murder mystery so far is the doctor. According to Herbert Schreier, joint author of the book and chief of psychiatry at the Children's Hospital Medical Center in Oakland, California, women like Allitt are escaping detection because of the complex relationships they have formed with the doctors treating the young patients who are harmed.

Last month Allitt, a 24-year-old nurse, was sentenced to life imprisonment on 13 charges of murder, attempted murder and assault on children.

Dr Schreier believes cases of the syndrome are less rare than the medical profession believes. In a paper published in the April edition of the American Journal of Orthopsychiatry, Dr Schreier and his co-author Dr Judith Libow report on a questionnaire to 1,258 American paediatricians asking for details of cases: they received 316 replies describing a total of 465 cases.

'This suggests that there may be large numbers of cases,' says Dr Schreier. 'We believe that many of them are not being diagnosed. For example, when cases are exposed there is often an older child who died a few years earlier in mysterious circumstances.'

Dr Schreier is one of America's leading experts on the syndrome and has investigated more than 30 cases in the past seven years, many of which have come to court. 'Existing theories about why these women torture children with unnecessary drugs and enemas and catheters usually claim it is do with seeking attention,' he says. 'But that doesn't begin to explain their sadistic glee at moments of crisis, and until we understand what is really happening we won't be in a position to detect it easily.'

These cases, which may involve mothers or women caring for children, are regarded as a mystery, he says, because all the attention focuses on how a woman could do such things to a child. 'But that is to miss the point. The key is that the woman regards the child as a fetishistic object, valuable only as a means of manipulating her relationship with the doctor, whom she considers to be a parent substitute. This not a sexual relationship. What these women want is both recognition and revenge. To get it they make both the child and the doctor their victims.'

The doctor is unaware of what is going on. Dr Schreier has noted that in each of his cases there has been an intense relationship between the woman and the doctor treating the child, but that the doctor was unable to see what was happening. 'These women leave a lot of clues. They tell lies that can be easily checked; they do things it's easy to detect like cutting feeding tubes. But the doctors involved don't notice.'

One of the questions that the inquiry into the Allitt case will investigate is how the nurse could have been allowed to carry on for so long after suspicions had been aroused. But according to Dr Schreier such delays are a defining feature of the syndrome.

'We had a very similar case in the States about 10 years ago involving a nurse called Genene Jones. Deaths and seizures were occurring on a children's ward and an analysis of the duty rota showed her to be present at every one, just like Allitt. What the authorities did was to move all the staff to other duties. One of the doctors on the ward then actually took Jones to work in her private practice and it wasn't until another three children suffered fits in a week that Jones was finally confronted.'

Why do doctors consistently fail to notice what is happening, and why are these women prepared to go to such desperate lengths to manipulate these relationships? The roots lie in childhood. 'At first I thought there would be a connection with sexual abuse,' says Dr Schreier. 'But we didn't find that. Instead we found neglect; as little girls they all had feelings of being humiliated and not valued.' Then at some point they got the attention they craved from a doctor or someone medical and became driven by two opposing forces: masochistic and sadistic.

They want security and recognition from the doctor - a parent substitute who can be male or female. 'These women are impostors. They are playing the role of the caring mother or nurse and they do it brilliantly; the parents of Jones's victims took out advertisements in the paper thanking her for all her care, just as Allitt was made a godmother. They also flatter and admire the doctors. Until you've encountered one, you can't believe how convincing they are.'

But at the same time they are hungry for revenge: they want to inflict punishment for the neglect they suffered as children. 'Just when some treatment seems to be working they launch another attack. But in their mind it is the doctor that is humiliated and made to look a fool. The child is just a pawn in a frequently deadly game they can't win, because the more successful they are at humiliating the doctor, the less they value the attention.'

According to this analysis, doctors are vulnerable to such an elaborate charade precisely because of their professional training, which has taught them to focus on solving clinical problems. They are also in thrall to a powerful social stereotype which says that mothers and nurses are sources of comfort and nurture.

'The sick children involved don't seem to fit any clinical pattern,' says Dr Schreier. 'Just when the doctor has got one diagnosis figured out, the woman will do something to make a mockery of it. This combination of apparent adulation from a mother or a nurse and an insoluble medical problem with the child can easily render the doctors involved unconfident about their judgements. And that is why they are so reluctant to act.'

In the book, Dr Schreier links the condition to anorexia. 'Although I didn't know about Allitt, the fact she has anorexia fits in perfectly. Women like her are bereft of feelings of self- worth but they are brilliant manipulators. Having lost a supply of babies as objects to control those around her, it's not surprising she resorts to using her own body as a weapon.'

What can be done to help doctors realise they are being manipulated? 'The most valuable thing they can do is talk to each other about their confusion over these cases,' says Dr Schreier. 'The major reason this goes undetected is because doctors feel a need to be smart and independent. If they have a problem they tend to try to solve it on their own. When we are called in the first thing we do is to get the doctors involved to discuss it together and suddenly what they couldn't see before becomes clear.'

'Hurting for Love', by Herbert Schreier and Judith Libow, is published in America by Guilford.