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Kate Bainbridge is a lively 37-year-old former schoolteacher. We are communicating in the conservatory of her parents’ home in south Cambridge. She has expressive eyes and a broad and ready smile, but she can utter only occasional single words with difficulty. She sits in a wheelchair “speaking” with the aid of a letter-board, using her left forefinger to spell out words individually.

Ten years ago, Kate went into a deep coma and was on a ventilator for several weeks. She had suffered severe brain inflammation after contracting a viral infection. When she came out of the coma, she opened her eyes and could breathe naturally, but she was unresponsive to speech and visual stimuli, and appeared to lack all conscious awareness. She was still in this condition four months after falling ill, and was later diagnosed to be in a persistent vegetative state, or PVS: in other words, persistently unaware. But the diagnosis was wrong.

Although Kate could not speak, or hear properly, or make any kind of signal, or take in sustenance except through a tube into the stomach, she was sometimes aware of herself and her surroundings. She had a raging thirst that was not alleviated by the ward staff. She was racked with pain. Sometimes she’d cry out, but the ward staff thought it was just a reflex action. Kate suffered so much pain and despair that she tried to take her own life by holding her breath.

Then a Cambridge neuroscientist called Dr Adrian Owen put her in a special kind of scanner and performed an unprecedented experiment. It revealed evidence of fluctuating levels of brain activation when she was presented with pictures of her parents. From that point, she started her long journey back into the world. This is a story about brain-impaired patients who come gradually out of coma into “minimal awareness” after being misdiagnosed as being in PVS: breathing, appearing to be wakeful, yet deemed to be dead to themselves and the world. It is also about the disastrous consequences of such misdiagnoses, estimated in the UK and other countries to be running at two in five cases. And, crucially, it is about a neuroscientific research programme that is set to transform the prospects of diagnosis, treatment and rehabilitation of brain-injured people the world over.

Only an estimated 20% of patients return, like the Top Gear presenter Richard Hammond after his car crash in September, to fully functioning normality after serious brain injury. The range of disability following brain damage is hugely varied in type and severity. It is not known how many PVS and minimally conscious patients there are in this country, since no central registry exists. It is likely, according to a canvass of many neurology professionals, to be in the tens of thousands. More certain is the grim reality of hospital wards and long-term care homes where the persistently vegetative and the minimally conscious languish, sometimes for decades.

To write this article I have had the sobering experience of witnessing the plight of patients with severely impaired consciousness – the intubations, the double incontinence, the stricken semicircle of wheelchairs parked before the unwatched day-room TV. And I have met the anguished families of those who are denied final grieving and closure for a loved one condemned to what appears a living death. All too often I have spoken to a wife or husband, or mother or father, who will travel anything up to two hours each way by taxi, every day, to spend time with an unresponsive child or spouse.

But here’s at least one mordantly amusing and true story told to me by a psychologist at Putney’s Royal Hospital for Neuro-disability. “Young man with motorbike head injury in a coma. His mum, a keen evangelical, comes every day with friends to sing Onward, Christian Soldiers by his bedside. She’s hoping to stimulate his brain into action. It works: he comes round, but he can’t speak. So they fit him up with one of those Stephen Hawking-type laptops, and the first words he speaks are: “For God’s sake, Mum, shut it!” That’s about as funny as it gets on a brain-injury ward, but there’s a serious take-home message. Even minimally aware patients can retain emotions, personality, a capacity to suffer – and, as the young biker showed, attitude.

The biggest, most tragic clinical myth about brain injury today is that PVS can be reliably diagnosed by bedside observation alone. It has in fact been known for at least a decade, ever since a key survey of brain-injured patients, that misdiagnosis of the condition runs at more than 40%, a statistic originally calculated by Professor Keith Andrews, former head of the Putney hospital, and confirmed by recent surveys in Europe and North America. This means that valuable rehabilitation strategies are routinely neglected, and misdiagnosed patients end up on unsuitable wards or in care homes where their needs are neither understood nor met.

Up to 12,000 people under 40 in this country suffer traumatic brain injury every year, and there are serious deficiencies in their rehabilitation, according to Professor John Pickard, head of neurosurgery at Addenbrooke’s hospital, Cambridge: “The tendency for patients to be left to languish on general medical, surgical and orthopaedic wards continues to their detriment.” The shocking term being used by campaigning neurologists and neurosurgeons is that unknown numbers of patients are being just “warehoused”.

Christine Simpson, a mother of two in her mid-fifties, and her husband, Colin, encountered the PVS misdiagnosis phenomenon two years ago. After suffering a brainstem stroke, Christine was first admitted to the intensive-care unit at the Princess Alexandra hospital, Harlow, then transferred to a general respiratory ward, where she remained for about a month.

“I was told that she would probably get a chest infection and not survive more than a few weeks,” says Colin. “Even on the respiratory ward I was told she was still in coma, though she was communicating with me at times through her eye movements. Only because myself and our two grown-up sons were constantly at her bedside did she get proper attention.

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