Somnology is the scientific study of sleep. It includes clinical study and treatment of sleep disorders and irregularities. Sleep medicine is a subset of somnology. Hypnology has a similar meaning but includes hypnotic phenomena.
History After the invention of the EEG, the stages of sleep were determined in 1936 by Harvey and Loomis, the first descriptions of delta and theta waves were made by Walter and Dovey, and REM sleep was discovered in 1953. Sleep apnea was identified in 1965. In 1970, the first clinical sleep laboratory was developed at Stanford. The first actigraphy device was made in 1978 by Krupke, and continuous positive airway pressure therapy and uvulopalatopharyngoplasty were created in 1981. The Examination Committee of the Association of Sleep Disorders Centers, which is now the American Academy of Sleep Medicine, was established in 1978 and administered the sleep administration test until 1990. In 1989, the American Board of Sleep Medicine was created to administer the tests and eventually assumed all the duties of the Examination committee in 1991. In the United States, the American Board of Sleep Medicine grants certification for sleep medicine to both physicians and non-physicians. However, the board does not allow one to practice sleep medicine without a medical license.
The International Classification of Sleep Disorders Created in 1990 by the American Academy of Sleep Medicine (with assistance from European Sleep Research Society, the Japanese Society of Sleep Research, and the Latin American Sleep Society), the International Classification of Sleep Disorders is the primary reference for scientists and diagnosticians. Sleep disorders are separated into four distinct categories: parasomnias; dyssomnias; sleep disorders associated with mental, neurological, or other medical conditions; and sleep disorders that do not have enough data available to be counted as definitive sleep disorders. The ICSD has created a comprehensive description for each sleep disorder with the following information.
Synonyms and Key Words – This section describes the terms and phrases used to describe the disorder and also includes an explanation on the preferred name of the disorder when appropriate. Essential Features – This section describes the main symptoms and features of the disorder. Associated Features – This section describes the features that appear often but not always present. Furthermore, complications that are caused directly by the disorder are listed here. Course – This section describes the clinical course and the outcome of an untreated disorder. Predisposing Factors – This section describes internal and external factors that increase the chances of a patient developing the sleep disorder. Prevalence – This section, if known, describes the proportion of people who have or had this disorder. Age of Onset – This section describes the age range when the clinical features first appear. Sex Ratio – This section describes the relative frequency that the disorder is diagnosed in each sex. Familial Pattern – This section describes whether the disorder is found among family members. Pathology – This section describes the microscopic pathologic features of the disorder. If this is not known, the pathology of the disorder is described instead. Complications – This section describes any possible disorders or complications that can occur because of the disease. Polysomnographic Features – This section describes how the disorder appears under a polysomnograph. Other Laboratory Features - This section describes other laboratory test such as blood tests and brain imaging. Differential Diagnosis – This section describes disorders with similar symptoms. Diagnostic Criteria – This section has the criteria that can make a clear-cut diagnosis. Minimal Criteria – This section is used for general clinical practice and is used to make a provisional diagnosis. Severity Criteria – This section has a three-part classification into “mild,” “moderate,” and “severe” and also describes the criteria for the severity. Duration Criteria – This section allows a clinician to determine how long a disorder has been present and separates the durations into “acute,” “subacute,” and “chronic. Bibliography – This section contains the references.
Diagnostic tools Somnologists employ various diagnostic tools to determine the nature of a sleep disorder or irregularity. Some of these tools can be subjective such as the sleep diaries or the sleep questionnaire. Other diagnostic tools are used while the patient is asleep such as the polysomnograph and actigraphy.
Sleep diaries A sleep diary is a daily log made by the patient that contains information about the quality and quantity of sleep. The information includes sleep onset time, sleep latency, number of awakenings in a night, time in bed, daytime napping, sleep quality assessment, use of hypnotic agents, use of alcohol and cigarettes, and unusual events which may influence a person's sleep. Such a log is usually made for one or two weeks before visiting a somnologist. The sleep diary may be used in conjunction with actigraphy.
Sleep questionnaires Sleep questionnaires help determine the presence of a sleep disorder by asking a patient to fill out a questionnaire about a certain aspect of their sleep such as daytime sleepiness. These questionnaires include the Epworth Sleepiness Scale, the Stanford Sleepiness Scale, and the Sleep Timing Questionnaire. The Epworth Sleepiness Scale measures general sleep propensity and asks the patient to rate their chances of dozing off in eight different situations. The Stanford Sleepiness Scale asks the patient to note their perception of sleepiness by using a seven-point test. The Sleep Timing Questionnaire is a 10-minute self-administration test that can be used in place of a 2-week sleep diary. The questionnaire can be a valid determinate of sleep parameters such as bed time, wake time, sleep latency, and wake after sleep onset.
Actigraphy Actigraphy can assess sleep/wake patterns without confining one to the laboratory. The monitors are small, wrist-worn movement monitors that can record activity for up to several weeks. Sleep and wakefulness are determined by using an algorithm that analyzes the movement of the patient and the input of bed and wake times from a sleep diary.
Physical examination A physical examination can determine the presence of other medical conditions that can cause a sleep disorder.
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