Since narcolepsy is a neurological disorder, it might seem strange that it’s listed as a diagnosis in a psychiatric manual. But if you take a look in the Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition (DSM-5), you’ll see narcolepsy there. It’s listed under the category of sleep-wake disorders. What is the DSM-5, and why are those categories there? Here’s an explanation.

What Is the DSM-5?

The Diagnostic and Statistical Manual of Mental Disorders is a guide psychiatrists and psychologists use to classify diagnoses by symptoms. It was first created in 1952 by the American Psychiatric Association. The DSM was inspired by the World Health Organization’s International Classification of Diseases, which is used to classify conditions by symptoms and etiology. That data can be used to study patterns from related and seemingly unrelated conditions. Similarly, the DSM was designed to bring together patterns of symptoms that psychiatric professionals had seen in practice and group them together in classifiable diagnoses.

DSM-5, the most recent edition, was first published in 2013. There are three main parts: diagnostic criteria, diagnosis classification, and descriptive text. The diagnostic criteria list the symptoms required for a diagnosis, and how long those symptoms must be present. Many conditions have notes to rule out diagnoses as well; these are conditions that cannot be present in a person receiving that diagnosis.

Diagnoses are further classified into a numbered system that groups related conditions. The descriptive text describes the symptoms, other features of the condition, associated diagnoses (comorbidities) and subtypes, known prevalence of the condition, and various diagnostic measures available for the condition — if there are any.

The DSM-5 includes 11 diagnostic groups of sleep-wake disorders, including narcolepsy. It also covers conditions like insomnia disorder, hypersomnolence disorder, obstructive sleep apnea, circadian rhythm sleep-wake disorders, rapid eye movement (REM) sleep behavior disorder, restless legs syndrome, and medication-induced sleep disorder.

Why Is the DSM-5 Important?

Some may assume that if a condition is in the DSM-5, that means that it doesn’t have a physical basis in the body. That is not the case. Neurological disorders that present physical signs in the central nervous system and also affect mental health are included.

One advantage of the DSM-5 is that it is designed for clinical practice. With simple sorting and classifications of symptoms, it allows any medical professional to reach a tentative diagnosis. It also gives doctors a common basis for the classification of symptoms.

Another advantage is that it can be used by doctors who are not experts in sleep. While sleep experts often know the signs of narcolepsy when they see them, most doctors are not as aware. However, a doctor can find the DSM criteria for narcolepsy if a person complains of those specific symptoms. The International Classification of Sleep Disorders (ICSD-3), created by the American Academy of Sleep Medicine, has criteria for narcolepsy somewhat similar to the DSM’s. But a clinician who is not an expert in sleep disorders wouldn't normally have the ICSD-3. The DSM-5 is much more well known and thus more accessible to both health care professionals and the general population.

What Is the DSM-5 Diagnostic Criteria for Narcolepsy?

In the ICSD-3, narcolepsy is divided into two different types (narcolepsy type 1 and narcolepsy type 2). In the DSM-5, the diagnosis of narcolepsy requires the main narcolepsy symptom of excessive daytime sleepiness (EDS) to occur at least three times per week for at least three weeks. In addition, one or more of the following signs is required to achieve any diagnosis of narcolepsy:

• Cataplexy (brief, bilateral loss of muscle tone)
• A deficiency of the hormone hypocretin, as indicated by levels in cerebrospinal fluid
• A formal nocturnal sleep study or multiple sleep latency test (MSLT) that shows abnormal REM sleep latency (elements of REM sleep at the beginning or end of the sleep cycle that may result in sleep paralysis)

The DSM-5 lists five types of specifiers that can be added to a narcolepsy diagnosis:

• Narcolepsy without cataplexy, but with hypocretin deficiency (the most common type)
• Narcolepsy with episodes of cataplexy, but without hypocretin deficiency (a rare subtype only seen in about 5 percent of those with narcolepsy)
• Autosomal dominant cerebellar ataxia, deafness, and narcolepsy (a rare DNA mutation that leads to dementia)
• Autosomal dominant narcolepsy, obesity, and type 2 diabetes mellitus (a rare glycoprotein gene mutation)
• Narcolepsy secondary to another medical disorder (a result of an infectious disease, a tumor, or trauma to the brain that causes the death of hypocretin-producing neurons)

Narcolepsy can fit into three categories of severity: mild, moderate, and severe. Mild narcolepsy means that cataplexy is infrequent and daytime sleepiness results in naps once or twice a day. A moderate case involves more frequent cataplexy and multiple episodes of daily napping, as well as disturbed nocturnal sleep. Severe narcolepsy involves chronic sleepiness, drug-resistant cataplexy (often with multiple attacks per day), and chronically disturbed nocturnal sleep episodes (insomnia, movements, vivid dreaming).

There is a diagnosis in the DSM-5 for those who have excessive daytime sleepiness but none of the other criteria: hypersomnolence disorder. Narcolepsy and other hypersomnolence disorders cannot be diagnosed in the same person — you either have one or the other.

Even with the DSM-5, narcolepsy is not always easy to recognize. It remains an underdiagnosed condition. However, the criteria in the DSM provides a basis for doctors who might not be sleep specialists to start the path to diagnosis.

Are you confused about the DSM-5 criteria for narcolepsy? Are you wondering about a diagnosis? Comment below or start a new conversation on MyNarcolepsyTeam.