Conversion disorder affects some 800,000 people in the UK alone.
The illness is defined as one that causes physical symptoms that appear neurological, including fits, numbness or paralysis, but where doctors cannot find an injury or condition to explain them.
It is also known as functional neurological disorder (FND), a term preferred by some campaigners who believe “conversion disorder” suggests that patients are converting their mental symptoms into physical ones.
Previous hypotheses of the cause have included severe mental health problems or an involuntary response to trauma.
It has also been linked to “hysteria”, the archaic term used in the past to describe a number of conditions believed to be caused by emotional excess.
But researchers at the University of York and Hull York Medical School have found the disorder could be caused by an inflammation reaction which affects DNA instructions to convert proteins, which are required for the structure and function of the body’s tissues and organs.
The Conversion and Neuro-inflammation Disorder Observational (Cando) study, the first of its kind, is supported by Tees, Esk and Wear Valley NHS Trust.
Professor Christina van der Feltz-Cornelis, of the University of York, said: “This is a very difficult condition for people to live with and one which is often overlooked because the medical profession doesn’t have the answers.
“People living with the condition can become very distressed and isolated, often losing jobs and social networks through being unable to communicate or being unwell. Patients can also suffer from memory and concentration problems.
“We made the discovery by examining levels of inflammation in blood samples from patients with FND that mimicked stroke-like symptoms. They were found to be higher than normal. Also, microRNA levels in the blood seemed to play a role and this influences the expression of genes in the cell.
“These preliminary results deserve further exploration and replication in larger samples before we can draw firm conclusions.”
The Cando researchers hope that the new study will help in the development of new treatments, as treatments previously given to people with conversion disorder have often not helped ease the symptoms.
Annie, a patient involved in the Cando study, said: “It is a relief to suddenly find that there may be a reason for this condition.
“I can’t wait for treatments that may be developed as a result of this work.”