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The Epidemiology and Diagnosis of Insomniania directly (and often prophylactically). Onthe other hand, chronic insomnia may bemore often related to intrinsic sleep disorders,primary insomnia, or chronic medicaland psychiatric conditions, and may requirea more extensive evaluation (includingassessment of comorbid conditions) in orderto delineate appropriate treatment. However,it should be stressed that the relationshipsbetween insomnia duration, etiology,and evaluation implications have not beenwell investigated.Insomnia can also be classified on thebasis of etiology into primary and secondarysubtypes. The term primary indicates thatthe insomnia is not caused by any knownphysical or mental condition but is characterizedby a consistent set of symptoms, adefined disease course, and a generalresponsiveness to treatment. 16,17 Althoughthe etiology of primary insomnia has yet tobe clarified, recent research implicatesendocrine, neurologic, and behavioral factorsas contributing to its pathogenesis. 18-20It is estimated that among patients diagnosedwith insomnia, 25% to 30% suffer fromprimary insomnia. 6,21 Secondary insomnia,in contrast, has been defined historically asinsomnia resulting from other medical andpsychiatric illnesses, medication use, orother primary sleep disorders. 5,22 The 2005NIH State-of-the-Science statement, however,has suggested the use of the termcomorbid insomnia, instead of secondaryinsomnia, based on a limited level of understandingof the causal relationships whichmay exist between insomnia and coexistingdisorders. Conceivably, primary insomniacould coexist as an independent entity inthe context of another disorder, as opposedto being caused by it. 5Epidemiology and Natural Historyof InsomniaEstimates of the prevalence of insomniaare variable because definitions and diagnosticcriteria for insomnia are inconsistent. Inaddition, the use of baseline and follow-upassessments to establish incidence and remissionrates can be problematic because ofthe wide spectrum of insomnia duration (eg,a positive finding of insomnia at baselineand 1-year follow-up may reflect unremittingchronic insomnia or 2 episodes of transientinsomnia). 23 Given these limitations, itis generally believed that 10% to 15% ofadults suffer from chronic insomnia, 24 usuallyregarded as a persistent insomnia lastingmore than 1 month, and an additionalone third have transient or occasionalinsomnia. 25The elderly in particular are affected,with an estimated prevalence ranging from13% to 47%. 22,26-31 The National Institute onAging’s Established Populations for EpidemiologicStudies of the Elderly (EPESE) 3-yearlongitudinal study showed that 42% of community-dwellingseniors who participated inthe survey had difficulty falling and stayingasleep. 26,32 Sleep difficulties were moreprevalent among seniors with physical disability,depressed mood, respiratory symptoms,or fair-to-poor perceived health andamong those using anxiolytic and barbiturateprescription medication. At the 3-yearfollow-up of EPESE, Foley et al estimatedincidence and remission rates for insomniain more than 6000 participants of the originalsurvey. 32 Among 4956 participants whohad no symptoms of insomnia at baseline,nearly 15% reported symptoms at the 3-year follow-up, suggesting an annual incidenceof 5%.In the same study, for about 15% of participants,insomnia symptoms resolved eachyear. Extrapolating these findings to the generalpopulation, the authors estimated that8 million elderly persons nationwide haveinsomnia on any given day, more than 1 millionnew cases of insomnia develop eachyear, and symptoms resolve in nearly 1.3million elderly persons annually. 32 Disturbedsleep is also associated with impairmentsin memory and attention, and can bemisinterpreted as signs of dementia in theelderly. 33Although most epidemiologic studiesindicate that women are more likely to havesleep difficulties than men, 27,34 the EPESEstudy reported comparable rates in bothsexes. The exception to this parity occurredin patients 85 years or older, in which theprevalence was higher among men. 32 TheEPESE study also showed that women wereless likely to achieve remission (46% ofwomen vs 52% of men), suggesting the high-VOL. 12, NO. 8, SUP. THE AMERICAN JOURNAL OF MANAGED CARE S215