Tuck’s Guide to Sleep Disorder Diagnosis
Biological markers for sleepiness do not exist the way they do for many illnesses. Although blood chemistry changes a little when a person is sleepy, the change is very small, serum levels of hormones differ widely, and the physiological systems that make a person sleepy and aroused are complicated.
Polysomnography is not widely used in the diagnosis of insomnia. It is expensive and the accepted clinical definition of insomnia incorporates the patient’s subjective assessment in a way that PSG cannot capture. Indeed, many people who clearly suffer from chronic insomnia show results in a PSG (under 30 min sleep latency, over 85% sleep efficiency) that would not suggest insomnia.
Further, many insomniacs think they were awake even when the PSG results show they were asleep. This has been documented by studies. So patient accounts of their own sleep may be unreliable.
A thorough examination and accurate diagnosis of insomnia requires the patient’s medical, psychiatric, and sleep history. It’s hard for the doctor to distinguish between primary and secondary insomnia, and what other maladies may be present. Insomnia, the most common sleep disorder, even has subtle differences in official definitions.
The International Classification of Diseases most recent guidelines (ICD-10) defines insomnia as
- Difficulty falling asleep
- Difficulty maintaining sleep, or
- Non-refreshing sleep
happening three or more times a week for longer than a month, and causing distress to the patient or interfering with the patient’s daily life.
The American Psychiatric Association’s DSM-IV (Diagnostic and Statistical Manual of Mental Disorders) likewise lists the criteria for insomnia as complaints about
for a period of a month and where the patient has distress or the insomnia interferes with his or her life.
The International Classification of Sleep Disorders (written by sleep professionals) includes waking up too early as a sign of insomnia and has no specific time before it can be diagnosed so long as some daytime impairment happens.
There is some suggestion that the type of insomnia can be classified by looking at daytime symptoms. Secondary insomnia from mental disorders and idiopathic insomnia result in high levels of daytime sleepiness and mood disorders in patients. Insomnia from paradoxical insomnia or psychophysiological insomnia results in daytime tension but not as much sleepiness during the day.
Standard questionnaires and scoring systems can help. More on prevalence of insomnia.
Lab Tests in Evaluation of Sleep Disorders
Laboratory tests of blood or urine are not employed to look for insomnia per se. Insomnia is a clinical diagnosis, meaning the doctor takes into account visible signs and what the patient tells him/her. Laboratory tests are ubiquitous in modern medical practice, and if they indicate something out of the ordinary (say iron deficiency which might be tied to restless leg syndrome or hyperthyroidism), that could be a clue to the cause of a patient’s insomnia.
Polysomnography has become the established test for diagnosis of sleep disorders in problem cases. Because it is expensive and time consuming, it is used only when there is cause for concern of a serious disorder. One common criterion for insomnia is a total of 30 minutes of waking from the time on sleep onset until morning rising, although some feel this simple criterion misses too many problems.
Actigraphy involves fitting the patient’s body with a device to record movement during the night. Simple actigraph machines are worn on the wrist and can be purchased for home use. The results from these tests are not as conclusive as from a polysomnography in determining sleep latency, sleep time, and transition between stages, but some doctors and sleep nurses find them useful.
Actigraphic assessment is also useful although like PSG the results often disagree with subjective assessment. To get an actigraphic reading, the patient wears a device on the wrist or ankle to measure motor activity during the night for a couple of weeks. Actigraphs are effective at distinguishing between primary insomnia and a circadian rhythm disorder. New home use devices that let users see their sleep architecture have been introduced, although they are not considered definitive for diagnosis of sleep disorders
Psychiatric tests may be administered if the doctor feels they are necessary. Sleep-specific tests such as the multiple sleep latency test (MSLT) are also employed. Many sleep experts employ the Pittsburgh Sleep Quality Index.
Blood and urine tests may be ordered as part of an overall physical examination or to look for specific problems that the doctor might worry about. Common problems sleep doctors might look for include iron deficiency, diabetes, and thyroid problems.
Because sleepiness and fatigue are symptoms of many illnesses, the doctor may request a complete blood count or blood differential to find out the breakdown of white blood cells in your system. Urinalysis tests are common, too. These can help rule out diseases or physiological disorders that might be causing your sleep problems. In serious, tough situations, a CT scan of the head may be ordered to look for signs of brain injury.
Sleep logs or diaries are also valuable to the diagnosing doctor. These diaries record bedtime, estimated time to fall asleep, number of awakenings, wake-up time, use of medicines, and subjective quality of sleep. These diaries are typically filled out in the mornings, and over a period of several months they can paint a picture of the patient’s situation for the diagnosing physician. More on sleep histories. Here is a roadmap for those with insomnia.
Patient interviews: Professional groups also recommend that doctors directly ask patients how they have been sleeping during a routine checkup. Surveys show most people who believe they have chronic insomnia have never discussed the problem with a doctor.