In Britain alone, a quarter of a million people are affected by an illness of uncertain cause. There is no treatment for myalgic encephalomyelitis, or chronic fatigue syndrome, but the condition has a long list of debilitating symptoms and consequences.
Lives are changed drastically in those with ME. In the young, education is disrupted or limited. In working adults, employment can become impossible – with knock-on financial and psychological effects. For all, social and family life is restricted.
Philippa Jennings, 26, has lived with ME for 23 years. She contracted glandular fever at the age of three, which left her with the condition. Viral infection is just one potential cause for ME, as well as immune dysfunction, hormonal imbalance and stress.
Life with ME
"Living with the condition is unpredictable," Philippa told IBTimes UK. "I have no idea how I am doing to feel from one hour to the next. I have been in a 'relapse' for about two years now, following an ill-advised stint in full-time work.
"The fact is I can't work full-time, and life has been easier since I accepted that."
At the moment, Philippa's ME is classified as mild to moderate. But this is the best she has felt in a long time, and there is no telling whether this period will last. In late 2012, Philippa suffered a severe relapse.
"It was the worst I have ever had," she recalled. "Before I relapsed, I had been accepted onto a Masters course in composition at Leeds College of Music. I had a full-time job in finance and was teaching too."
"I had taken on too much and found myself getting confused and exhausted," Philippa said. "At home, I crawled from one room to another as my legs wouldn't hold me."
She bought a wheelchair after being put on a three-month waiting list for an assessment.
"It was fantastic, I could get around the shops and be out for hours without being in agony or collapsing."
ME is recognised as a medical condition by a number of organisations – including the World Health Organisation and the Royal Colleges of Physicians, Psychiatrists and General Practitioners – but a diagnosis of the condition still poses a problem.
The symptoms of ME are present in a number of other medical conditions, which means there has to be a process of elimination. The most prevalent symptom is severe fatigue following mental or physical activity is a predominant symptom of ME – the full extent of which often only becomes apparent between 24 and 48 hours afterwards.
Long-lasting flu symptoms, muscle pain, cognitive dysfunction, sleep disturbance, irritable bowel symptomatology and problems with the nervous system, such as fainting, are also common. Some ME sufferers develop depression or anxiety as a result of persistent symptoms.
Tony Britton, of the ME Association, said ME blights lives. "From suffering a flu-like illness that never seems to go away, to delayed recovery after any form of mental or physical exertion and being bed-bound, ME is debilitating. Those with the condition can be plagued by bright light, loud noises and in some cases, fed by tube because the swallowing muscles do not work."
"Any number of allergies and sensitivities wash around in its wake, with unpleasant reactions to certain foods, cleaning fluids, bowel and bladder disorders and sensitivity to extremes of temperature," he added.
Philippa received a diagnosis when she was ten.
"I had been a sickly child for years I had test after test – one doctor suggested I was deaf, another suggest epilepsy, but I had an electroencephalogram which came back normal," she said.
"I was a child, and children aren't supposed to get exhausted. The fatigue enveloped me for months," Philippa explained. "I was referred to a paediatrician and tested for everything.
"Within minutes after receiving test results, the doctor said 'chronic fatigue syndrome - it's a textbook case' – and that was the first time I had ever heard of it. The advice to my parents was 'take her out of school, and wait'."
While knowledge of the condition is improving, sufferers are still being blamed for their own illness.
"There are no psychological quick fixes for serious, classic ME, but there is mounting evidence that it is caused by a barrage of neurological, immunological and endocrinological assaults on the body," Britton said.
However, he added, the evidence is largely ignored.
During Philippa's relapse in 2012, she was still working full-time but felt she could not tell her work – despite struggling to be able to walk.
"I knew I should have told my employers, but I had bitter experience of misunderstanding the illness, so I didn't until it got really bad," she said. "It turns out they were fantastic, allowing me to work part time and use my wheelchair when I got worse."
But people have not always been sympathetic. Philippa applied for a disabled parking permit twice, but was told ME was a temporary illness, so she would not be eligible.
"Although I'm not using my wheelchair right now, there is no way of knowing how long I would be ill for – and no treatment. A lot of people are wheelchair-bound for years, and the fact this is caused by ME should not be a reason to deny someone their badge."
When she relapsed in 2009, Philippa was told there were no specialists in West Yorkshire – and given a sick note. But things are slowly improving.
"In my last relapse, I was referred to an ME clinic in Leeds and received support and advice. If you are diagnosed with a condition like this, it can be frightening and feel hopeless. You are transformed from a functioning human being to one that can't hold their weight off the ground – and you are told to manage your symptoms and wait," Philippa said.
"Can you imagine being told this when you are a mother working full time? Or a young person starting their career? It is the uncertainty that comes with the illness that is the worst."
Philippa is now self-employed and able to teach music from home. She has regular visits from friends, but has to rest regularly.
There is no treatment for ME, but headway has been made in understanding the illness. In October, Stanford University scientists found clear differences in the brains of people with ME, compared to those without the condition. Published in the journal Radiology, CFS patients had less overall white matter – the nerve tracts that carry information around the brain.
"We want the UK to be a better place for people with the condition, so ME Association campaigns for it to be widely recognised and taken more seriously," Britton said. "We also fund biomedical research into the illness – with the hope that one day science will find that elusive cure."