They performed a systematic review of studies containing original data on long-COVID reviewing the frequency and characteristics of neurological symptoms, looking for positive evidence suggesting an underlying functional disorder, and the hypothesised causes of long-COVID. 102 studies were included in the narrative synthesis. The most consistently reported neurological symptoms were cognitive difficulties, headaches, pain, dizziness, fatigue, sleep-related symptoms, and ageusia/anosmia. Overall, they found no evidence that any authors had systematically looked for positive features of FND. An exception were three studies describing temporal inconsistency. In general, the neurological symptoms were insufficiently characterised in order to support or refute a diagnosis of FND. 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. Only one study hypothesised that some people with long-COVID might have a functional disorder, and another 8 studies a chronic fatigue syndrome-like response. The authors concluded that neurological symptoms are prevalent in long-COVID, but poorly characterised. They also found similarities between some manifestations of long-COVID and functional disorders triggered by acute illnesses. Unfortunately, the current literature is plagued by confounders, including the mixing of patients with initial mild infection with those with severe acute medical complications. The hypothesis that long-COVID might in part correspond to a functional disorder remains untested.
Teodoro T, Chen J, Gelauff J, Edwards MJ. Functional Neurological Disorder in people with Long-Covid: A Systematic Review. Eur J Neurol. 2023 Jan 31.
doi: 10.1111/ene.15721