According to researchers at London’s St. George’s Hospital, acute health disorders like viral infections can spur what’s called functional neurological disorder (FND) in vulnerable people. Could a proportion of people experiencing neurological Long COVID symptoms actually have FND? The St. George scientists explored this question, and the answers can have significant implications for diagnosis and treatment.*

About FND

Mayo Clinic describes FND as a newer, broader term for nervous system-related symptoms that don’t fall under any known neurological disease or medical condition. These include symptoms that:

• Are not psychosomatic, and lead to real distress and difficulty functioning 
• Vary in type and severity, and can be erratic or persistent
• Affect movement and/or the senses
• Stem from changes in brain function, not from damage to brain structure 
• Respond to early diagnosis, treatment, and patient education

What the researchers did

The St. George researchers undertook a systematic review of 102 studies involving more than 400,000 COVID-19 patients, to examine neurological symptoms, evidence suggesting FND, and perceived causes of Long COVID.

• Patients were mostly 40-59 years old with about equal proportions of men and women.
• About 12,000 people had Long COVID, while the rest were screened for Long COVID over time.
• 89 studies (87%) defined Long COVID as four (4) weeks or more of post-viral symptoms.
• Neurological symptoms most often reported were:
  • Cognitive issues
  • Headaches
  • Dizziness
  • Pain
  • Fatigue
  • Sleep-related issues
  • Loss of smell and/or taste

What they found

Across all studies, the researchers found that a diagnosis of FND couldn’t be supported or rejected based on the original analyses of neurological symptoms. Except for several studies that described temporary inconsistency of symptoms, none of the studies had looked for evidence of FND. On top of that, just 13 studies had looked at Long COVID following mild infection, where the general effects of a severe disease would no longer be added factors.

What it means

The possibility that a portion of people diagnosed with Long COVID may actually have FND has been largely untested and overlooked, the researchers concluded in the European Journal of Neurology. At the same time, they “remain struck by the similarities between some manifestations of long COVID and functional disorders triggered by acute illnesses.”

This is problematic, both for clinicians’ understanding of Long COVID and for patients. It means delayed diagnosis and treatment for people who may actually have FND, which could affect disease outcome. “[FND] is a condition with specific diagnostic criteria and for which effective treatments are available,” said study co-author Tiagro Teodoro, M.D., Ph.D.

Each year, FND occurs in up to 12 of every 100,000 people. According to Mark Hallet, M.D., former head of medical neurology for the National Institute of Neurological Disorders and Stroke (NINDS), “[I]t is likely that some Long COVID patients do have FND, or FND together with some other pathology. The most important issue is that FND requires its own treatment and that such treatment can be successful.” 

Doctors and researchers need to “appreciate the likely complexity” of Long COVID and be aware of FND, says Teodoro. “A key feature is [symptom] inconsistency over time.” He noted that COVID-19 infection and vaccination have spurred an increase in FND incidence, making his team’s findings “even more surprising.”

*George, J. (2023, February 14). Long COVID or Functional Neurological Disorder? MedPage Today. https://www.medpagetoday.com/neurology/longcovid/103108