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The belief that long COVID might be related to a functional neurological disorder (FND) remains untested, a systematic review showed. Across 102 long COVID studies, neurologic symptoms were insufficiently characterized to support or refute a diagnosis of FND, reported Tiago Teodoro, MD, PhD, of St. George’s Hospital in London, and colleagues.

MedPage Today’s recent article entitled, “Long COVID or Functional Neurological Disorder?” says that with the characteristics of the disorder, some people with FND might be inappropriately considered to be long COVID patients, which could delay diagnosis and treatment and impact prognosis, the researchers wrote in the European Journal of Neurology.

“We remain struck by the similarities between some manifestations of long COVID and functional disorders triggered by acute illnesses,” Teodoro told MedPage Today. “Our systematic review shows that the possibility that some people labeled as having long COVID might be experiencing a form of functional neurological disorder has, so far, been largely overlooked in the medical literature,” he said.

“This is a major problem for understanding long COVID but primarily for patient management, as this is a condition with specific diagnostic criteria and for which effective treatments are available,” he added.

FND refers to disorders caused by an abnormality in brain signaling with no significant structural damage in the brain. It occurs in an estimated four to 12 people per 100,000 per year.

“These are common neurological conditions caused by malfunctioning of the brain but not directly related with structural damage,” Teodoro noted. “We have previously seen many patients developing functional neurological symptoms following an acute event such as an injury, an invasive medical procedure, or an infection, among many others,” he said.

“These factors do not directly cause the functional neurological symptoms, but are best understood as triggers, which precipitate this condition in people with a pre-existing predisposition,” Teodoro continued. “In some cases, these functional neurological symptoms might become persistent.”

Teodoro and co-authors emphasized that a diagnosis of functional neurologic symptoms is positive and not just based on ruling out other conditions. “A key feature is inconsistency over time, which means that symptoms often occur intermittently and/or with fluctuating severity,” they wrote.

Teodoro and his group looked at 102 studies spanning 412,726 who had COVID-19. Of these, 31 studies recruited participants who had long COVID (11,860 patients). The remaining studies looked at people with acute COVID screened for ongoing long COVID symptoms. Overall, 51 studies were prospective, 33 were cross-sectional, and 12 were retrospective; 18 included a control group. Most (89 studies) defined long COVID as symptoms persisting for four weeks or more. Neurologic symptoms reported most consistently were cognitive difficulties, headaches, pain, dizziness, fatigue, sleep-related symptoms and ageusia or anosmia.

“Overall, we found no evidence that any authors had systematically looked for positive features of FND,” Teodoro and colleagues wrote. “An exception were three studies describing temporal inconsistency.”

“Moreover, only 13 studies specifically focused on long COVID after mild infection, where the impact of confounders from the general effects of severe illness would be mitigated,” they added.

Reference: MedPage Today (Feb. 14, 2023) “Long COVID or Functional Neurological Disorder?”