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 Researchers found that people with knee osteoarthritis and insomnia
were also more likely to suffer from a nervous system disorder
called “central sensitization” that makes them more sensitive to
pain and lowers their threshold for tolerating discomfort.
“Knee osteoarthritis patients with insomnia have more pain and worse
physical function than knee osteoarthritis patients without
insomnia,” lead study author Claudia Campbell, a psychiatry
researcher at Johns Hopkins University School of Medicine in
Baltimore, said by email.
Osteoarthritis is a degenerative disease that erodes cartilage, the
slippery tissue that covers the ends of bones in a joint, causing
pain, swelling, loss of motion and bone spurs. It is associated with
aging. It typically strikes the most used joints, including the
knees, hips, fingers and lower spine.
Globally, about one in 10 men and one in five women over age 60 have
osteoarthritis, one of the leading causes of disability in developed
nations, according to the World Health Organization.
About a third of adults have insomnia, or difficulty falling or
staying asleep, at least briefly. Around one in 10 people have
chronic insomnia that’s more severe, striking at least three times a
week for three months or more, according to the American Academy of
Sleep Medicine.
Campbell and colleagues compared pain in four groups: 118 patients
with insomnia and knee osteoarthritis, 31 people with the joint
disorder but normal sleep patterns, 30 healthy people with insomnia,
and 29 healthy individuals with no trouble sleeping.
People with insomnia took more than 30 minutes to fall asleep, or
they had at least two awakenings a night of more than 15 minutes or
at least one awakening for more than 30 minutes – and they had these
problems on at least three nights a week for a month or more.
Healthy patients in the study had no history of chronic pain over
the past three years and no major medical or psychiatric illnesses.
Study participants kept sleep diaries, did one-night sleep studies
in a laboratory to verify the quality of rest they got, and took
pain threshold tests using heat and cold.
The knee osteoarthritis patients were significantly older than their
healthy peers, reported higher levels of pain and depression, and
were more likely to be overweight.
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Among participants with insomnia, those who also had knee
osteoarthritis reported more sleep interruptions and had less “sleep
efficiency,” the authors report in the journal Arthritis Care and
Research.
Sleep efficiency is determined by how much time you spend asleep
after you go to bed and turn the lights off.
Researchers also measured signs of what’s known as central
sensitization, a nervous system condition linked to long-term
exposure to chronic pain that makes people have a lower pain
threshold.
Patients with knee osteoarthritis and insomnia were most sensitive
to pain, based on assessments of central sensitization, the study
found.
While sleep patterns have long been linked to pain perception, the
study sheds new light on how insomnia transforms pain perception
through central sensitization in people with knee osteoarthritis,
said Dr. Gillian Hawker, a researcher in musculoskeletal diseases at
the University of Toronto who wasn’t involved in the study.
But the study can’t prove that insomnia causes pain, because it’s
hard to say which problem developed first, Hawker said by email.
“People with a lot of joint pain have difficulty sleeping, which can
result in greater fatigue and depressed mood and pain severity,”
Hawker said. “Physical activity, which is the primary therapy for
knee osteoarthritis, helps sleep, pain, mood and functioning.”
SOURCE: http://bit.ly/1JKO7Xm Arthritis Care and Research, online
June 4, 2015.
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