Insomnia Classifications: Are They Clinically Useful?

Article Outline

• Abstract
• Introduction
• Developing an Insomnia Nosology
• Insomnia Nosologies
• Diagnostic Reliability
• Validity of Insomnia Classification Systems
• Concordance of Insomnia Classification Systems
• Clinical Utility of Insomnia Classification Systems
• Practical Implications
• References
• Copyright

Abstract 

Insomnia is caused by a variety of physiologic, emotional, environmental, or behavioral conditions. As such, patients with insomnia complaints represent a heterogeneous group. A diagnostic classification system that appropriately and reliably assists in distinguishing or differentiating insomnia subtypes is vital because treatment decisions are largely determined by the eventual insomnia diagnosis assigned. This article reviews the evolution of insomnia classification systems and briefly describes those in current use. Subsequently, these classification systems are evaluated by considering their reliability, validity, and utility in clinical applications. In addition, limitations of the existing insomnia nosologies are discussed, and methods for countering these limitations are considered.

Keywords:  Insomnia classification , insomnia diagnosis , reliability , validity

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Introduction 

Chronic insomnia is a highly prevalent and often debilitating condition ascribed to multiple causes, including primary disorders of sleep, medical conditions that include chronic pain, psychiatric illnesses, and use or abuse of medications or illicit substances.¹, ², ³, ⁴, ⁵, ⁶, ⁷, ⁸, ⁹, ¹⁰ Given this multitude of causative factors, patients with insomnia represent a rather heterogeneous group that can be divided into many distinctive subgroups. Over the past several decades, several nosologies, or diagnostic systems for classification of insomnia subgroups, have been developed. In their clinical applications these nosologies facilitate clinician-to-clinician communication and guide decisions about treatment, prognosis, and administrative procedures.¹¹ Such nosological classification systems are highly relevant to advanced practice nurses (APNs) because they are often the first clinicians to encounter the patient with insomnia. This article provides a history and description of the nosologies developed for insomnia classification. In addition, the discussion highlights a number of shortcomings inherent in these systems and provides suggestions for their future improvement.

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Developing an Insomnia Nosology 

The steps typically involved in the development of a nosology include (1) obtaining professional sponsorship, (2) assembling an “expert” panel, (3) selecting an appropriate framework for grouping the disorders of interest, (4) choosing possible diagnostic categories and subcategories, (5) arriving at a consensus about those categories, and, finally, (6) writing up the nosology. Factors that can influence the ultimate structure of the classification system include the unique characteristics and dynamics of the consensus panel and practical considerations such as coding and reimbursement. Often, diagnostic systems developed for other disorders are examined for strengths and weaknesses to guide and optimize the new classification system. In all cases, research about insomnia phenotypes, as well as clinical experience, and case studies are important when developing a new classification system.

Under ideal circumstances, diagnostic classification of related medical disorders is based on their clearly defined and distinctive pathophysiologies. In the case of insomnia, however, classification has been largely dependent on factors such as symptom presentation (ie, sleep onset or sleep maintenance problems), sleep laboratory findings, clinical utility, expert experience, and consensus, because much remains unknown about the cause and pathophysiology of insomnia per se.¹¹ Nonetheless, over the past several decades, considerable efforts have been devoted to the development of insomnia classification systems. The history and results of these efforts are reviewed briefly in the ensuing discussion.

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Insomnia Nosologies 

Several organizations, including professional sleep societies, the World Health Organization, and the American Psychiatric Association (APA), have published insomnia classification systems. A historical account and description of the major insomnia nosologies published thus far are provided in Table 1. As suggested by the information in this table, these systems have differed in the number and types of insomnia categories they describe. In general, these systems have either tended to “lump” patients with insomnia into a few fairly global categories or “split” such patients into a much larger number of more highly specific subtypes. Given their clear differences, it is obvious that these systems can lead to markedly discrepant diagnostic assignments in their clinical applications. As such, it is important for the APN to consider what the research reveals about each of these systems before selecting one for ongoing clinical use. The choice of a system can only be based on weighing the facts and considering whether an existing system is working—an empirical decision.

Table 1. Brief History of Insomnia Classifications

Source: International Classification of Sleep Disorders: Diagnostic and Coding Manual. American Academy of Sleep Medicine, 2005.

In an effort to improve the diagnostic utility of the International Classification of Sleep Disorders (ICSD), the classification system was recently updated (Table 1, ICSD 2). In addition, a “crosswalk” between ICSD 2 and ICD-9 codes has been developed to assist with comparison of these two systems (available at: www.aasmnet.org/PDF/CrosswalkCard.pdf).¹²

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Diagnostic Reliability 

If a classification system is to be useful, clinicians using the system should generally agree in their diagnostic assignments when independently evaluating the same group of patients. That is to say, the system should be easy enough to use such that there is good reliability between clinicians who use the system. To date, relatively little research has examined the reliability of insomnia nosologies, and results of such research has provided mixed results. Tests of the APA nosologies (ie, the DSM-III-R and DSM-IV systems) have shown good inter-rater agreement for insomnia diagnoses when clinicians use pre-prepared highly structured interviews,¹³ but only modest agreement when they use the unstructured interviews typically used in usual clinical practice.¹¹ Similar impressions are derived from the few reliability tests¹⁴, ¹⁵, ¹⁶ of the ICSD nosology, although these studies have failed to provide information about the reliability of many of the insomnia diagnoses in this system. To date, interclinician agreement for insomnia diagnoses listed in the International Classification of Diseases (ICD) remains unexplored. Given the current status of this research, it appears that the available insomnia nosologies have only modest reliability. As such, there currently is little assurance that clinicians will consistently agree about their insomnia diagnoses regardless of the specific classification system they chose. The APN who is familiar with these classifications is in a position to assess whether a particular system has utility in the clinical setting and may be able to gather information that could be useful in future decisions about the use of such systems.

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Validity of Insomnia Classification Systems 

The key question in evaluating the validity of classification systems is, “when the diagnostic system is applied, does the subsequent clinical classification subdivide heterogeneous groups of patients into ‘true’ or naturally occurring homogeneous subgroups?” Whereas establishing the validity of a specific diagnosis is not particularly difficult, verifying the validity of an entire classification system is challenging from a procedural standpoint. However, one previously used method to test the validity of insomnia nosologies is that of comparing classification results derived from clinical evaluations with those derived from a computer-based statistical method known as cluster analysis. As outlined in Figure 1, the cluster analysis is conducted with a set of variables thought to be relevant, which in the case of insomnia might include data about nature, duration, and frequency of sleep complaint; daytime symptoms; medical history; psychiatric history; age; sex; and so forth.

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• Figure 1. 

  Cluster Analysis: Methodology

To date, two cluster analyses have been performed on insomnia classification systems. In the first,¹⁷ the Association of Sleep Disorders Centers (ASDC) classification system was evaluated, and results showed that only 2 of 9 empirically derived clusters consisted only of patients with a single clinically assigned ASDC diagnosis. The second study¹⁴ tested both the DSM-III-R and ICSD systems and found that none of the 14 empirically identified clusters was homogeneous in their clinically assigned diagnoses. Of course, in the case of these studies it is possible to argue that differences between the clinical and empirical groupings resulted because important discriminating variables were inadvertently omitted from the statistical cluster procedure. Nonetheless, in both studies the types of data considered in assigning clinical diagnoses were included in the cluster procedures, and collectively these studies tested 3 distinctive nosologies. Given these considerations, it would seem that these studies raise serious questions about the validity of each of the systems scrutinized.

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Concordance of Insomnia Classification Systems 

Additional concerns about the available insomnia nosologies come from studies that have evaluated the diagnostic concordance achieved when 2 or more insomnia nosologies are applied to the same group of patients. The purpose of such studies is mainly that of detecting consistency from one classification system to the next. Two classification systems may be considered consistent with one another when patients viewed as diagnostically homogeneous by one classification are homogeneous according to the second classification system. However, if 2 classification systems applied to the same patients lead to discrepant or inconsistent diagnostic assignments, such outcomes raise questions about the utility of one if not both classification schemes (see Side Bar).

Unfortunately, the 2 studies conducted to examine concordance among current insomnia nosologies have provided discouraging results. In the first of these little diagnostic concordance was observed across nosologies when the DSM-IV, ICSD, and ICD-10 were used to assign insomnia diagnoses to the same large patient group.¹⁸ A second study conducted with a large community sample showed that only 39.8% of those who qualified for an ICSD insomnia diagnosis also met criteria for a DSM-IV insomnia diagnosis; the remainder were not viewed as having insomnia by DSM-IV criteria.¹⁶ Considered collectively, results of the cluster and concordance studies suggest that the current insomnia nosologies may not accurately reflect all clinically important characteristics of patients with insomnia and may, hence, have questionable validity in the clinical setting.

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Clinical Utility of Insomnia Classification Systems 

Inasmuch as the various insomnia classification systems have enjoyed fairly widespread use in clinical settings, an additional important metric for evaluating these systems is their perceived or proven utility in clinical applications. In this regard, a recently reported survey study solicited evaluations of the ASDC, ICSD, ICD-9CM, and DSM-IV nosologies from a sample of 206 clinicians who practiced at accredited sleep centers in the United States.¹¹ Results of that survey showed the ICSD and ASDC were rated more highly than the DSM-IV and the ICD-9CM on such qualities as overall organization, “fit” to patients, and ease of use (Figure 2). Although the DSM-IV and ICD systems enjoy wide use for clinical diagnosis and billing purposes, sleep experts in the study sample perceived these systems to be less useful than the more complex ICSD system for evaluating sleep disorders.

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• Figure 2. 

  A Comparison of Nosologies

• Clinicians answered the following questions about 4 sleep disorders classification systems: “How would you rate the organization of sleep disorder categories and diagnoses?”; “How well do the diagnoses ‘fit’ your patients?”; and “How easy is the system to use?” The nosologies were rated on a scale of 1 (very poor) to 5 (excellent) for the first two questions, and 1 (very difficult) to 4 (very easy) for the third question. Answers of “Don't know” were excluded. Horizontal bars across columns indicate classification systems that were not significantly different from each another in post-hoc analysis. For significant differences, P < 0.001.(Reprinted with permission from: Buysse DJ, Young T, Edinger JD, Carroll J, Kotagal S. Clinicians' Use of the International Classification of Sleep Disorders: Results of a National Survey. Sleep. 2003;1:48-51.)

In addition to the issues considered thus far, it is of practical importance to determine how well the available insomnia nosologies guide treatment decisions. In one study of this question sleep specialists were asked to consider a standard list of treatment recommendations for patients they assigned DSM-IV and ICSD diagnosis.¹⁹ The specialists rated each treatment on a 4-point scale as “first-order treatment recommendation” (a rating of 1) through “not recommended” (a rating of 4). Analyses of treatment choices showed that the clinicians' treatment decisions were guided by diagnostic decisions. The top 4 treatment recommendations for some of the most common diagnoses are shown in Figure 3, Figure 4. In the case of DSM-IV primary insomnia, for instance, all of the most strongly indicated interventions were behavioral and psychoeducational in nature. In contrast, the most strongly recommended interventions for insomnia related to a mental disorder included withdrawing or prescribing medications and psychiatric treatment. Similar sorts of results were noted for ICSD categories. These findings imply that insomnia treatment is strongly guided by diagnostic impressions derived from the ICSD and DSM-IV nosologies. Thus, despite the many limitations of these current nosologies, they have seemingly proven useful in the realm of insomnia management.

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• Figure 3. 

  How Do DSM-IV Diagnoses Impact Treatment Decisions?

• Differing DSM-IV insomnia diagnoses were found to result in differing treatment modalities. For primary insomnia (n = 48), circadian rhythm disturbance (n = 16), and substance-induced sleep disorder (n = 6), the most strongly preferred interventions were usually non-medicinal (solid bars), while for insomnia related to a mental disorder (n = 99), pharmaceutical interventions (striped bars) were among the most strongly recommended. Adequate sleep hygiene was an important component in all cases. (Reprinted with permission from Edinger JD. Classifying insomnia in a clinically useful way. Journal of Clinical Psychiatry. 65(Suppl8), 36-43, 2004. Copyright, 2004, Physician's Postgraduate Press. Adopted or reprinted by permission).

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• Figure 4. 

  How Do ICSD Diagnoses Impact Treatment Decisions?

• Differing ICSD diagnoses were found to result in differing treatment modalities. For psychophysiological insomnia (n = 30), delayed sleep phase syndrome (n = 16), and cases of inadequate sleep hygiene (n = 13), the most strongly preferred interventions were usually non-medicinal, while for insomnia related to a mood disorder (n = 69) or anxiety disorder (n = 13), pharmaceutical interventions were among the most strongly preferred. As for DSM-IV diagnoses, proper sleep hygiene was an important component of treatment recommendations. (Reprinted with permission from Edinger JD. Classifying insomnia in a clinically useful way. Journal of Clinical Psychiatry. 65(Suppl8), 36-43, 2004. Copyright, 2004, Physician's Postgraduate Press. Adopted or reprinted by permission).

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Practical Implications 

Although it is clear that existing insomnia classification schemes have some proven utility, their limits to reliability and validity suggest that these systems would benefit from further refinements. Moreover, the marked differences in their overall structures, conceptualizations of insomnia, and number of insomnia categories delineated creates costly variability in the assessment and clinical management of patients with insomnia as well as needless disunity among insomnia researchers who use these alternate systems to anchor their empirical studies. Fortunately, recent collaborative efforts among parties responsible for future versions of the current insomnia nosologies lend hope for greater consistency among further revisions of these systems. Despite these collaborative efforts many questions remain about how to most effectively classify insomnia patients to assure reliable, valid, and clinically useful diagnoses. To address these questions, several steps are needed. More empirical data about reliability, validity, predictive value, and clinical usefulness of the current and future generation insomnia nosologies must be collected. It also will be useful to determine how well these nosologies perform in predicting treatment response and course of insomnia disorders over time. To maximize diagnostic reliability and ensure reproducible diagnoses, it will be necessary to minimize the degree of clinician interpretation by improving the specificity of diagnostic criteria.

Until an optimal insomnia classification system is developed, the APN, as a clinician observer, can contribute to the body of knowledge needed to make decisions about the utility and choice of classification systems. An understanding of the current insomnia nosologies can help the APN to evaluate which classification may have utility in her or his practice setting. The nosologies may help the APN to develop an insomnia diagnosis. In addition, the use of simple questions about the patient's ability to fall asleep, stay asleep, whether the sleep impairment has consequences for functioning the next day, and the duration of sleep problems may guide understanding of the insomnia complaint and aid in treatment planning.

A number of available questionnaires can be used to assess the sleep/wake complaints of insomnia patients, including (1) the Epworth Sleepiness Scale,²⁰ (2) a scale for assessing sleep hygiene,²¹, ²² and (3) other assessments in a Nursing Clinics of North America book²³ and an insomnia textbook.²⁴ These publications may provide the APN with the tools for patient evaluation. Patient sleep logs are also useful assessment tools. A sample sleep log can be found in the booklet, Insomnia: Assessment and Management in Primary Care, from the National Institutes of Health, available at: www.nhlbi.nih.gov/health/prof/sleep/insom_pc.pdf²⁵

Awareness of the range of causes of insomnia suggested by currently available insomnia nosologies may assist in one day achieving a working diagnosis and instituting proper management strategies for APNs and all practitioners involved in the care of patients with insomnia.

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