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COVID-19 vaccination can be one of a number of events that may trigger functional neurological disorder (FND), experts said.

Two cases of young women manifesting FND after COVID-19 vaccination were reported by Alfonso Fasano, MD, PhD, of the University of Toronto, and Antonio Daniele, MD, PhD, of Università Cattolica del Sacro Cuore in Rome, in a letter to the .

Two other published reports showed probable FND precipitated by COVID-19 vaccine administration, highlighting that FND should be considered when assessing post-vaccine neurologic symptoms, wrote Matthew Butler, MD, of Kings College London in England, and co-authors in the .

FND involves a disruption in normal brain mechanisms for controlling the body. It can be triggered by physical or emotional events including head injury, medical or surgical procedures, or vaccinations. People with FND may present with a range of neurological symptoms such as seizures, sensory abnormalities, gait or balance disturbance, or weakness. FND is distinct from feigning because patients perceive their symptoms as involuntary. Once it is recognized and diagnosed, .

"We strongly encourage clinicians to be aware of the possibility for FND in response to SARS-CoV-2 vaccinations," Butler told 乌鸦传媒. "FND can be a serious and debilitating condition; however, it does not implicate any vaccine constituents and should not hamper ongoing vaccination efforts."

"Making clinicians aware of this can benefit people with FND reactions to vaccines, as well as maintaining public confidence in the vaccine," Butler added. "Rigorous causality assessments should occur when FND reactions are suspected."

"Among the various adverse events which might be observed after COVID-19 vaccination, the occurrence of functional -- once called psychogenic -- neurological disorders might be a challenging issue for healthcare providers, media, and public opinion with a negative impact on vaccination campaigns," noted Fasano and Daniele.

"In our view, FND following COVID-19 vaccination will not be a rare phenomenon and will be widely covered by the media, being interpreted as a direct consequence of the vaccine, as already seen in the past," they wrote.

The first case from Fasano and Daniele involved a woman who presented with a short episode of generalized psychogenic non-epileptic seizures 20 minutes after receiving her second dose of the Pfizer-BioNTech vaccine. The event was followed by different episodes that included an inability to move her whole body. No post-ictal period followed these episodes, some of which were captured by video-electroencephalography and did not show any epileptic activity.

The second patient had persistent dizziness and reported loss of tactile sensitivity in her right arm and leg about 2 weeks after receiving the AstraZeneca vaccine. Her brain CT scan was unremarkable, and neurological examination did not show objective loss of tactile or pain sensitivity.

"In both patients, neurological symptoms were characterized by a sudden onset and overt inconsistency, as typically observed in patients with FND," Fasano and Daniele wrote.

The cases reported by Butler and colleagues involved previously healthy women, both in their 30s. One had probable FND after her first dose of the Pfizer-BioNTech vaccine; the other, after her first Moderna shot.

"The close development of functional motor symptoms after the vaccine does not implicate the vaccine as the cause of those symptoms," observed Alberto Espay, MD, MSc, of the University of Cincinnati, who was not involved with the case reports.

"Correlation does not imply causation," Espay told 乌鸦传媒. "If neurological symptoms following vaccination are determined to be functional during a neurological exam, then the vaccination can only be considered a stressor or precipitant, much like any other stressor might, such as a motor vehicle accident or sleep deprivation."

Earlier this year, a group led by David Perez, MD, MMSc, of Massachusetts General Hospital in Boston, published a paper in that discussed videos that had emerged on Facebook, YouTube, and other channels showing people with severe neurological symptoms, such as convulsions and difficulty walking, after receiving a COVID-19 vaccine.

"The spread of these videos could fuel vaccine hesitancy by giving an overly simplistic impression of potential links between the vaccine and major neurological symptoms," Perez said in a statement. "Instead, these are symptoms of a real, brain-based disorder that sits at the intersection of neurology and psychiatry."

"It is recognized that physical events such as head injury, surgeries, or vaccinations in some individuals can precipitate the development of FND," Perez told 乌鸦传媒. "In such instances, one of the important mechanisms is the attention drawn to the body."

Neurologists and other healthcare professionals have an obligation to explain FND to the public, he added.

While health experts have tried to stress that in most cases, there is no direct link between COVID-19 vaccines and various media-covered adverse events, more needs to be done, Fasano and Daniele noted.

This is especially true in light of misinformation and conspiracy beliefs about the COVID-19 pandemic, which are "now enriched by the theories of anti-vaccine movements," they wrote. "We suggest that the medical community should be more vocal in informing the media and public opinion about FND, thus making a further step towards the establishment of 'eHealth literacy.'"

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