Subtyping primary insomnia: is sleep state misperception a distinct clinical entity?

Among the range of primary insomnia subtypes, those assigned such labels as subjective insomnia or sleep state misperception historically have been among the most intriguing yet challenging to understand and manage clinically. Such patients who produce seemingly normal polysomnograms often present rather compelling and, at times, dramatic sleep complaints. Our earliest formal sleep nosology included a separate diagnostic category for such individuals, but little research has been devoted to this insomnia subtype in the 20 years since this classification scheme was proposed. As a result, use of diagnoses such as subjective insomnia or sleep state misperception have remained controversial. The current article reviews this controversy and highlights the major criticisms forged against subdividing primary insomnia into objective and subjective subtypes. Subsequently, the relative merits of these criticisms are considered in view of early and recent findings vis-à-vis the subjective/objective insomnia dichotomy. Although available data are not conclusive, there appears to be sufficient evidence to suggest subjective and objective insomnia subtypes may suffer from distinctive forms of sleep-related pathophysiology. We conclude by advocating continued study of the subjective insomnia phenomenon and by providing specific directions for relevant future research.