INSOMNIA: SYMPTOM OR DIAGNOSIS?
Section snippets
DEFINITION OF INSOMNIA
There are three diagnostic schedules that present diagnostic criteria for insomnia; the Diagnostic and Statistical Manual of Mental Disorders, 4th Edition (DSM-IV; American Psychiatric Association, 1994), the International Classification of Sleep Disorders, Revised (ICSD-R; American Sleep Disorders Association, 1997), and the International Classification of Diseases, 10th Edition (ICD-10; World Health Organization, 1992). The diagnostic criteria for insomnia across the three classificatory
IS INSOMNIA A SYMPTOM OF OTHER DISORDERS?
Although this section will begin by discussing insomnia as a symptom of physical illness, most of the discussion in the present paper will center on insomnia and its relationship to psychological disorder. The reason for this emphasis is two-fold; insomnia as a symptom of a psychological disorder is 10 times more frequent than insomnia related to a physical illness (Ford & Kamerow, 1989) and the association between insomnia and psychological disorder raises important questions relating to cause
IS INSOMNIA COMORBID WITH OTHER DISORDERS?
The answer to this question relies on studies that have included an assessment of the prevalence of insomnia along with an assessment of the presence of a range of other psychological disorders. Unfortunately, the number of studies reporting comorbidity between insomnia and other disorders is limited as insomnia is typically not assessed in epidemiologic studies (Canals et al., 1997). Possible accounts of this omission include: (1) the assumption that insomnia is trivial and secondary to other
IS INSOMNIA SECONDARY TO OTHER DISORDERS?
The evidence reviewed thus far indicates that insomnia is a symptom of a range of medical and psychological disorders and is often comorbid with a range of other psychological disorders. Does being a symptom and a commonly comorbid disorder necessarily relegate insomnia to the role of ‘secondary’ diagnosis? It may be helpful to examine the precedent set by high comorbidity between other psychological disorders. Canals et al. (1997) reported high levels of comorbidity between all disorders
DOES INSOMNIA EVER OCCUR WITHOUT A COMORBID DISORDER?
Evidence that a significant proportion of insomnia cases occur in the absence of comorbidity would further strengthen the case against insomnia being the ‘secondary’ disorder and conversely, would strengthen the case for it being an important clinical entity in its own right. Several studies have reported high rates of insomnia without any comorbidity. The rate of insomnia in the absence of another psychological disorder is 10% in a community adult sample (Ford & Kamerow, 1989), 54% of a sample
FUTURE DIRECTIONS
With some exceptions (Weissman et al., 1997), the literature has been dominated by an almost exclusive focus on comorbidity between mood disorders and insomnia. It is critical that research assessing longitudinal relationships be expanded to include investigation of insomnia and a range of psychological disorders. In particular, the proposal that somatization plays a mediating role in the relationship between insomnia and comorbid psychological disorders (Frisoni, de Leo, Rozzini, & Bernardini,
CONCLUSION
Insomnia has been widely regarded as ‘secondary’ to or an epiphenomenon of another psychological disorder. This paper has presented evidence suggesting that insomnia is indeed a symptom of and comorbid with a range of psychological disorders. However, the idea that this implies that insomnia is ‘secondary’ is unfounded as: (1) depression is predicted by the presence of prior insomnia, (2) an effective intervention for the primary disorder does not necessarily alleviate the insomnia, and (3)
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