Functional neurological disorder in people with long COVID: A systematic review.

Observed Findings

• Cognitive difficulties, headaches, pain, dizziness, fatigue, sleep problems, and loss of taste/smell were the most consistently reported neurological symptoms across long COVID studies.
• No studies systematically searched for positive diagnostic features of functional neurological disorder.
• Only three studies documented temporal inconsistency in symptoms, a hallmark feature sometimes seen in FND.
• Only 13 studies focused specifically on long COVID following mild initial infection, limiting ability to distinguish functional mechanisms from effects of severe acute illness.
• Current literature mixes patients with mild and severe acute infections, introducing significant confounding.

Inferred Conclusions

• Neurological symptoms in long COVID are prevalent but insufficiently characterized to support or refute an FND diagnosis.
• The striking similarities between some long COVID manifestations and infection-triggered functional disorders warrant formal investigation.
• Methodological confounders—particularly mixing mild and severe cases—prevent reliable testing of the FND hypothesis in long COVID.
• Systematic prospective studies with rigorous characterization of neurological symptoms are needed to determine whether FND mechanisms operate in long COVID.

Remaining Questions