A rise in the frequency of hallucinations and nightmares could be an early warning sign of autoimmune diseases like lupus, according to a study.
Researchers called for doctors to ask about nightmares in the hope it could help detect when symptoms are likely to flare up in patients earlier.
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The study by University of Cambridge and King's College London included a survey of 676 people with lupus, a disease which causes the immune system to attack tissues and organs, and 400 clinicians.
It also included detailed interviews with 69 people living with various chronic inflammatory autoimmune disorders, including lupus, and 50 clinicians.
Researchers asked patients about the timing of 29 neurological and mental health symptoms, including depression, hallucinations and loss of balance.
In interviews, patients were asked to list the order in which symptoms usually occurred.
A little fewer than one in four people reported hallucinations, although the majority said this did not occur until around the onset of the disease or later.
However, interviews found three in five patients with lupus and one in three with other rheumatology-related conditions had a spike in vivid, distressing nightmares before having hallucinations.
Lead author Dr Melanie Sloan of the University of Cambridge, said: "It's important that clinicians talk to their patients about these types of symptoms and spend time writing down each patient's individual progression of symptoms.
"Patients often know which symptoms are a bad sign that their disease is about to flare, but both patients and doctors can be reluctant to discuss mental health and neurological symptoms, particularly if they don't realise that these can be a part of autoimmune diseases."
One patient described their nightmares as "horrific, like murders, like skin coming off people".
They added that they thought this happened when they were "overwhelmed" and "the more stress my body is under then the more vivid and bad the dreaming would be".
Professor David D'Cruz, of King's College London, added: "For many years I have discussed nightmares with my lupus patients and thought that there was a link with their disease activity.
"This research provides evidence of this, and we are strongly encouraging more doctors to ask about nightmares and other neuropsychiatric symptoms - thought to be unusual, but actually very common in systemic autoimmunity - to help us detect disease flares earlier."
The study, published in eClinicalMedicine, also found using the word "daymare" rather than hallucination was more effective for patients.
Some interviewees with lupus were also misdiagnosed with mental health problems.
A nurse told researchers she had seen patients "admitted for an episode of psychosis".
Prof Guy Leschziner, a study author and neurologist at Guys' and St Thomas' hospital, said: "This is the first evidence that nightmares may also help us monitor such a serious autoimmune condition like lupus, and is an important prompt to patients and clinicians alike that sleep symptoms may tell us about impending relapse."
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