[MSLT: an objective method of assessment of excessive sleepiness]

Excessive daytime sleepiness is a serious medical problem. It appears against patient will, when he performs normal day activities. It significantly disturbes daily functioning and may be a cause of a serious accidents. Approximately 5% of the general population suffers from excessive daytime sleepiness. The most common cause of daytime sleepiness is sleep deprivation. It is also a symptom of many disorders and may be an effect of taking many drugs, especially sedative ones. Investigation continued in the seventies by W. Dement and M. Carscadon resulted in preparation of MSLT which became the most widely used, objective method of the assessment of excessive sleepiness. It has been quickly used in diagnosis of narcolepsy, obstructive sleep apnea, idiopathic hypersomnia, periodic limb movements, circadian rhythms disorders, insomnia investigations, clinical assessment of many drugs. However equipment requirements are not that complicated, but investigator knowledge and experience are the limitations of the method. We described the protocol of the test including EEG procedures, patient preparation, interpretation of the results and normal values. Indications for MSLT in the diagnosis of sleep disorders were outlined with the special emphasis on narcolepsy.