When Kate Weston's brain was attacked by a deadly virus, her family were told to expect the worst. But then doctors tried a radical treatment

When, last August, Kate Weston started experiencing headaches and dizzy spells, she thought she was suffering from exhaustion. At the time, she had two jobs - as a nursery assistant and as a nanny - and assumed running around after children all day was taking its toll.

Unbeknown to Kate, 27, she was in fact experiencing the first effects of a virus that was to have a devastating effect on her life. By the time she went to bed that night complaining of a bad headache, her brain was already swelling within her skull, causing encephalitis. That, in turn, caused damage to her brain which resulted in the condition status epilepticus, which affects 14,000 people in Britain a year, causing them to have epileptic seizures constantly.

Although 50 per cent of status epilepticus patients have some sort of pre-existing epileptic condition, the rest, like Kate, are simply unlucky. Certain areas of the brain are vulnerable to seizures after damage caused by accidents, swelling or viruses. Within a month of her first headache, Kate was in intensive care on a life-support machine in a drug-induced coma, and doctors were baffled as to how to treat her.

That Kate is on the road to recovery today is only thanks to the pioneering work of doctors at London's National Hospital, who as a last resort turned to the drug ketamine. It's a horse tranquilliser, better known as a result of its popularity in the rave scene, where the clubbers who use it to get high call it "Special K".

Kate is still in hospital, where she is undergoing intensive physiotherapy and speech therapy, but her family and the doctors who treated her are confident that without the controversial drug she wouldn't be here today.

"Kate was always the fit and healthy one in the family," says her father Trevor, 57, a betting-shop manager who lives in Basingstoke with his partner, Avril, 50. "Just weeks before she fell ill, we'd been on a walking holiday in Devon and she'd been holding my hands, literally pulling me up all the hills.

"To see her lying in intensive care with tubes coming out of her mouth and nose, her face swollen from all the drugs she was being given, was simply incomprehensible.

"It all happened so suddenly. Kate had only been complaining of headaches for a few weeks and although she was admitted to hospital for scans, the doctors seemed to think she just had a bad migraine. Then, out of the blue, she had a huge seizure, her lips went blue, her mouth opened wide and her whole body started convulsing. Afterwards, the doctors asked her to write down her name and address, and she couldn't do it. Even then, they still seemed to be saying it was a migraine, but I was terrified. I said to them that I'd never heard of a migraine sending someone into a fit."

Trevor's fears were realised when later that night, once he'd returned home leaving his daughter in hospital, he received a call to say Kate had had another fit and had been transferred to intensive care. When he arrived at her bedside, she was on a life-support machine, and he was told her chances of survival were not good.

"By the time I reached Kate, she was under sedation and had a tracheotomy in her throat to help her breathe," says Trevor. "Her face was bright red, her temperature was over 40 degrees and her heart rate reached 198. You don't have to be a genius to know that people can't survive for long in that state. Nothing the doctors did seemed to help."

In November, after three months under permanent sedation, Kate was transferred to the Harris Neuromedical Intensive Care Unit at London's National Hospital and placed under the care of neurologist Dr Nick Hirsch, who specialises in rare forms of epilepsy.

"I always try to be honest with the family of patients such as Kate," says Dr Hirsch. "When I first saw her, I didn't really think there was much hope for her future. She had really been on all the conventional drug treatments for status epilepticus.

"Whenever her sedation was reduced, her fits began again. I also had concerns about what state she'd be in even if we did manage to stop the fits. Just having cells firing abnormally for a short period of time can cause irreversible brain damage, and Kate had been in this state for three months."

Kate underwent further tests. Her father and his partner travelled two hours a day to sit by Kate's bedside, where they talked to her even though no one knew if she could hear. But by Christmas her prognosis was still no better, and Kate had also developed blood poisoning.

"It was probably the worst Christmas of our lives," recalls Trevor. "It was the only day we didn't visit Kate in hospital - we'd made the journey every day and we were exhausted - but we telephoned her and a doctor held the phone to her ear. We might as well have gone and spent the day as usual, because we ended up sitting at home feeling thoroughly depressed."

It wasn't until April that things changed. Dr Hirsch, who had been scouring medical literature for inspiration, came across a report about ketamine. It described a case similar to Kate's which had been alleviated by the drug. "I don't know why people take ketamine for pleasure as really it is a horrible, horrible drug," says Dr Hirsch. "But I realised perhaps it could help Kate. It works by blocking NMDA receptors in the brain, which are thought to be instrumental in causing some of the damage that leads to abnormal epileptic activity. Both Kate's family and I felt we had nothing to lose."

Initially, the ketamine seemed to have little impact. Dr Hirsch ordered the dosage to be doubled, and 48 hours later, EEG scans suggested the seizures in Kate's brain were beginning to abate. Every day her condition improved, and within a week she was off life support.

Her recovery since, however, has been far from straightforward. Although able to breathe unaided, Kate was confused, weak, did not recognise her family and seemed to have lost her speech, too.

"It wasn't until about a month later that she made any sound at all," says Trevor. "We were terrified she'd lost her voice completely. But one afternoon, we wheeled her outside for the first time, and as soon as the sun hit her face she made a sound. It gave us hope that one day she'd talk again."

In June, Kate was transferred to a specialist rehabilitation unit at Southampton General Hospital and under their care her faculties have started to return. However, her ability to read, write, talk and carry out tasks has been seriously impaired.

"It's been very difficult for Kate, and she's become quite depressed about it," says her father. "But she's getting there. She's regaining her coordination. She's working out on an exercise bike every day and is very active. She loves going shopping and has recently been out to her favourite nightclub with her sister. There are definitely signs the Kate we all knew and loved is returning to us."

And Dr Hirsch is confident that Kate will carrying on recovering. "What Kate has achieved so far is remarkable," he says. "She smiles at jokes, for instance, and it takes an awful lot of computing power in the brain to be able to do that. Kate is one of our success stories."

Kate's story is shown in 'The Brain Hospital', BBC1, 9pm, tomorrow