[6] The Diagnostic and Statistical Manual of Mental Disorders (DSM) has historically used the term in its definition of delirium.
[12] In clinical practice, no standard test is exclusive and specific; therefore, the diagnosis depends on the physician's subjective impression.
The DSM-IV-TR instructs clinicians to code subsyndromal delirium presentations under the miscellaneous category "cognitive disorder not otherwise specified".
[22] Barbara Schildkrout, a clinical instructor in psychiatry at the Harvard Medical School, described her subjective experience of clouding of consciousness, which she also called "mental fog", after taking a single dose of chlorpheniramine (an antihistamine for her allergy to cottonwood) on a cross-country road trip.
"[3] Cognition includes perception, memory, learning, executive functions, language, constructive abilities, voluntary motor control, attention, and mental speed.
[26] Many people with fibromyalgia experience cognitive problems[28] (known as "fibrofog" or "brainfog"), which may involve impaired concentration,[29][30][unreliable medical source?
[34] A 2018 meta-analysis found that the largest differences between fibromyalgia patients and healthy subjects were for inhibitory control, memory, and processing speed.
[35][36][37] It is alternatively hypothesized that the increased pain compromises attention systems, resulting in cognitive problems.
[34] In chronic fatigue syndrome, also known as myalgic encephalomyelitis, the CDC's recommended criteria for diagnosis[38] include that one of the following symptoms must be present:[38] Lyme disease's neurologic syndrome, called Lyme encephalopathy, is associated with subtle memory and cognitive difficulties, among other issues.
[40] While it is unclear how the disease leads to brain fog, proper treatment with levothyroxine has been shown to reduce cognitive impairment.
[41] The emerging concept of sluggish cognitive tempo has also been implicated in the expression of brain fog symptoms.
[42] Patients recovering from COVID-19 report experiencing brain fog, which can reflect a wide variety of neurological and psychological symptoms linked to COVID-19.