SEIDs

Systemic Exertion Intolerance Disease (SEID) is a term proposed for the illness more widely known as myalgic encephalomyelitis and chronic fatigue syndrome (ME/CFS). Introduced in a 2015 report by the Institute of Medicine (now the National Academy of Medicine), SEID was intended to emphasize the central role of exertion intolerance and the systemic nature of the condition. Some authors also use the plural form SEIDs to refer to the range of presentations encompassed by the syndrome, though most sources treat SEID as a singular diagnosis.

Core features of SEID include a substantial reduction or impairment in activity levels that persists for six months or more, post-exertional malaise (PEM) characterized by extended symptom flare after physical or mental activity, and unrefreshing sleep. In addition, individuals typically experience either cognitive impairment or orthostatic intolerance, and share a history of symptom duration and exclusion of other medical or psychiatric causes. There is no single laboratory test to diagnose SEID; diagnosis is clinical and aims to rule out other conditions with similar presentations.

Pathophysiology remains uncertain and is the subject of ongoing research. Proposed mechanisms include immune and autonomic dysfunction, neuroendocrine abnormalities, and metabolic disturbances, with infections frequently identified as possible triggers. Treatment is primarily supportive and multidisciplinary, focusing on symptom management, graded activity for some patients, sleep regulation, and addressing comorbid conditions.

Reception and use of SEID have been mixed. Some patient groups and clinicians prefer ME/CFS or CFS as terms, citing concerns about stigma or scope. While SEID has influenced diagnostic discussions, many guidelines and researchers continue to use established labels, with emphasis on core symptom criteria and individualized care.