Definitions of Insomnia
First created | 12/01/2011
Last edited |
- Ohayon MM. Epidemiology of insomnia: what we know and what we still need to learn. Sleep Med Rev. 2002 Apr;6(2):97-111.
More than fifty studies of insomnia based on data collected in various representative community-dwelling samples or populations were published with highly variable rates
These surveys provide estimates of the prevalence of insomnia according to four definitions:
- insomnia as a symptom
- insomnia as a symptom with daytime consequences
- insomnia as a Global Sleep Dissatisfaction (GSD, Ohayon 1993)
- insomnia as a diagnosis (according to the psychiatric classification or the one of the sleep specialists).
THE FIRST DEFINITION
The first definition is based on insomnia as a simple criteria. Four major criteria are commonly used:
- Difficulty Initiating Sleep
- Difficulty Maintaining Sleep
- Early Morning Awakening
- Non Restorative Sleep
Many epidemiological studies used one of these 4 criteria to qualify a subject to be insomniac. However, Early Morning Awakening is a troublesome symptom: how should "early" be defined in the general population?
According to this classical way, in our studies we found that about one-third of the general population presents at least one of them. These results give an inflated point of view about insomnia in the general population.
THE SECOND DEFINITION
The second definition takes into account the fact that a subject with one of the 4 previous criteria must also have daytime consequences before he can be considered insomniac.
According to this definition of insomnia, many researchers found a prevalence of insomnia between 9% and 15% in the general population. These results are much lower than those corresponding to the first definition.
THE THIRD DEFINITION
The third definition is based on the concept of Global Sleep Dissatisfaction (GSD, Ohayon 1993). This concept is based on the paradigm that "insomnia is first defined by the subject himself, by his persistent complaint (at least 6 months) about the quality or the quantity of his sleep" (Ohayon, 1994). According to this definition, several studies found a prevalence of insomnia of 8-18% of the general population. This prevalence is close to the one found for the second definition. However, the subjects of the second and third definition have not the same characteristics.
THE FOURTH DEFINITION
This last definition gives to the concept of insomnia a status of disease: insomnia is defined as a complete entity including a set of criteria and different conditions. Primary and secondary insomnia are distinguished. The psychiatric and sleep classifications define different sets of diagnoses. A Differential Diagnostic Procedure must be applied in order to validate the positive diagnosis. This procedure is an elimination procedure aiming to explore all concurrent diagnoses.
Using this decision-making process including a differential diagnosis, we found that the prevalence of insomnia as a diagnosis (according to the DSM-IV classification) is 6% (Figure 1).
A part of the population with GSD does not reach a diagnosis. This means that a part of the subjects complaining about their sleep cannot find a place in the Insomnia Diagnosis Category of the DSM-IV. Moreover, another part of the population does not present any criteria of insomnia as defined by the DSM-IV or the ICSD.
These four definitions of insomnia have higher prevalence rates in women than in men. However, this difference disappears when using a criterion of duration: chronic insomnia (for at least 6 months) is not gender-related. This is why GSD with its definition including a duration of 6 months does not change with gender while the other definitions are.
The prevalence of insomnia symptoms generally increases with age, while the rates of Global Sleep Dissatisfaction and Insomnia Diagnoses have little variation with age.
Moreover, GSD and Insomnia Diagnoses have a discrepancy of 1 to 5%. We showed that the DSM-IV classification is now taking into account a certain class of people presenting GSD, but not the 4 insomnia symptoms. Again, we must stress that someone may have one or several insomnia symptoms and still be happy with his sleep! On the contrary, GSD is pointing directly to the pathological cases.
Future epidemiological studies should focus on the natural evolution of insomnia.
Epidemiological genetic links of insomnia are yet to be studied.
Ohayon MM. Epidemiology of insomnia: what we know and what we still need to learn. Sleep Med Rev. 2002 Apr;6(2):97-111.