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Clinical features and diagnosis of chronic fatigue syndrome (systemic exertion intolerance disease)

Stephen J Gluckman, MD
Section Editor
Mark D Aronson, MD
Deputy Editor
Howard Libman, MD, FACP


Chronic fatigue syndrome (CFS), also known as systemic exertion intolerance disease (SEID), has received considerable attention but remains a complicated and controversial disease [1]. Much of this is due to the lack of objective findings. Nonetheless, patients with CFS/SEID have real symptoms and are not malingerers. The prevalence of this syndrome is unclear in part due to difficulties in proving the diagnosis.

The condition has long been recognized and many different terms have been used to describe it (eg, DaCosta's syndrome, effort syndrome, soldier's heart, neurasthenia, myalgic encephalitis/encephalomyelitis, Iceland disease, Akureyri disease, and Royal Free disease, chronic fatigue and immune dysfunction syndrome) [2,3].

The clinical manifestations and diagnosis of CFS/SEID are reviewed here. The general approach to a patient with fatigue and the treatment of CFS/SEID are discussed separately. (See "Approach to the adult patient with fatigue" and "Treatment of chronic fatigue syndrome (systemic exertion intolerance disease)".)


There are multiple case definitions for CFS/SEID, and these have changed over time [4-9]. In 2015, the Institute of Medicine (IOM) redefined the diagnostic criteria for CFS/SEID (table 1) and suggested the name change to systemic exertion intolerance disease [9]. The IOM diagnostic criteria focus on the most specific features of the disease. As with previous definitions, symptoms should be present for at least six months and have moderate, substantial, or severe intensity at least one-half of the time. Other criteria include: postexertional malaise, sleep problems, cognitive impairment, and orthostatic-related symptoms.

These clinical case definitions are standard epidemiologic tools that are employed when there is no diagnostic test for a specific disorder. They are "intentionally restrictive, to maximize the chances that research studies will detect significant associations if such associations truly exist" [7]. Though a clinical case definition is a well-established instrument, its strict application may not always be appropriate in the evaluation of a specific patient.

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Literature review current through: Nov 2017. | This topic last updated: Nov 15, 2017.
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