Periodic Leg Movements Predict Total Sleep Time In Older People With Cognitive Impairment, Sleep Disturbance

The study, authored by Kathy C. Richards, PhD, of the University of Pennsylvania, focused on 102 people (58 men and 44 women) between the ages of 59-96 years who had a clinical diagnosis of cognitive impairment (categorized as unspecified, Alzheimer disease, other, mixed, multi-infarct, and mild cognitive impairment) as well as average nightly sleep of seven or less hours and daytime sleep of 30 minutes or longer.

Ten characteristics associated with sleep disturbance (including PLMI, time in bed, cognitive status, painful conditions and depression) were assessed with one night of polysomnography. The participants also submitted to a Mini-Mental State Examination (MMSE), a 30-item standardized screen of orientation, registration, short-term memory, attention/concentration, language, and constructional capacity items. MMSE scores range from zero to 30, with greater numbers indicating higher cognitive functioning.

The average MMSE score was 17.3. In addition, 21.6 percent had at least one painful condition and 45.1 percent were diagnosed with depression. The participants' average PLMI was 17.3 with 33.3 percent having a PLMI greater than 15. Time in bed at night exceeded eight hours, yet participants averaged only 5.5 hours of sleep. PLMI, time in bed, and age explained 43.6 percent of the variance in total sleep time.

"Sleep disturbance in persons with Alzheimer disease and related dementias is a highly prevalent and disabling symptom that often leads to caregiver exhaustion and institutionalization for the person with dementia," said Dr. Richards. "Sedative-hypnotics are not effective and often worsen daytime cognitive functioning and cause nighttime falls. This study demonstrates that frequent periodic leg movements at night are predictive of reduced total sleep time in older adults with Alzheimer disease and related dementias. This finding is important because treatment of periodic leg movements may result in improved nighttime sleep and improved quality of life in this vulnerable population."

Periodic leg movement disorder (PLMD) is a condition that causes people to jerk and kick their legs every 20 to 40 seconds during sleep. As with restless legs syndrome, PLMD often disrupts sleep -- not only for the patient, but the bed partner as well. One study found that roughly 40 percent of older adults have at least a mild form of PLMD.

The article "Periodic limb movements predict total sleep time in persons with cognitive impairment and sleep disturbance"  was published in the February 1 issue of the journal Sleep.