Which clinical conditions are responsible for impaired alertness?

The complaint of excessive daytime sleepiness, commonly encountered in clinical practice, may arise from many medical and psychiatric disorders and behavioural lifestyle changes. The list of possibilities spans virtually every major area of medicine, neurology and psychiatry. Assessment of impaired alertness is largely based on clinical interview and direct observation, but it may also include subjective self-report, objective physiological and behavioural measures, and performance tests. In the primary care setting, a clear and detailed history is invaluable in negotiating these numerous diagnostic considerations. Primary care physicians need to be aware that the patient's complaint may be expressed in terms of 'tiredness' or 'fatigue' rather than a direct reference to impaired alertness or performance. Accurate diagnosis is important, not only because of the negative impact of impaired alertness and its possible underlying causes on health and the quality of the patient's professional and social life, but also because impaired alertness due to poor sleep quality can be remedied with appropriate treatment. Increased understanding of the neurological basis of alertness and sleepiness will undoubtedly lead to improved treatments. 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.