What is Multiple Sleep Latency Test (MSLT)

A study of brain activity during sleep, conducted to help determine the causes of sleep disturbances and daytime sleepiness. The MSLT, conducted in a sleep laboratory, consists of five 20-minute periods during which the person is in a darkened room and encouraged to fall asleep. For two hours between each sleep session the person must stay awake. An electroencephalogram (EEG), for which electrodes attached to the scalp transmit electrical messages from the brain to a recording mechanism, captures changes that occur between waking and sleeping states.

The neurologist analyzes the electrical patterns to determine whether there are patterns that point to pathological causes of the sleep problems. Narcolepsy (a neurological disorder in which the person suddenly and uncontrollably falls asleep), for example, has a particular pattern of electrical disturbance. The main reason for a person with Parkinson’s to have an MSLT is to rule out pathological causes of sleep disturbances and daytime sleepiness. The neurologist might request an MSLT when adjustments to the anti-parkinson’s medication regimen do not alleviate the symptoms. Typically, Parkinson’s disease does not cause discernible disturbances in the brain’s electrical activity during waking or sleeping periods.