Which clinical conditions are responsible for impaired alertness?

To facilitate improved understanding of the symptoms, aetiology, pathophysiology and treatment of impaired alertness, classification of the sleep disorders is necessary to discriminate between disorders. Based on recent advances in knowledge about sleep disorders, the recently published second version of the International Classification of Sleep Disorders (ICSD) has been expanded to include 85 sleep disorders under eight major categories: (1) insomnias, (2) sleep-related breathing disorders, (3) hypersomnias not due to a breathing disorder, (4) circadian rhythm sleep disorders, (5) parasomnias, (6) sleep-related movement disorders, (7) other sleep disorders, and (8) isolated symptoms, apparently due to adverse effect of drugs, medications and biological substances. The ICSD provides relevant information on the diagnostic features and epidemiology to differentiate between sleep disorders, and it will no doubt serve as a core resource in the development of recommendations for primary care physicians to guide the diagnosis and treatment of patients with impaired alertness.