By Dr Gareth Parry (ONZM, MB, ChB, FRACP)
Emeritus Professor, Neurology, University of Minnesota, USA
Clinical Senior Lecturer, Otago University, Wellington, NZ
Research Professor, Nelson-Marlborough Institute of Technology, NZ
Visiting Neurologist, Wellington Hospital, NZ
GBS Support Group Medical Advisor
Medical Advisory Board, GBS/CIDP Foundation International
A few weeks ago I wrote that COVID-19 did not appear to trigger GBS. Has anything changed? Probably not but I need to stress again that “…..my answers (were) based on what knowledge we currently have” and “that this is a rapidly evolving field and recommendations may change as we learn more”. There is a change in the information regarding GBS and COVID-19 but is that change meaningful? Let’s look at the facts.
A week ago, a single case of COVID-19-associated GBS was reported. The case was seen in January, early in the course of this pandemic, and the GBS occurred prior to the diagnosis of COVID-19 infection. Eight days after being admitted to the hospital with GBS the patient developed cough and fever and was diagnosed with COVID-19 infection. There are a few reasons to suspect that the association is no more than coincidental:
- In this reported case, the GBS occurred prior to symptomatic infection whereas GBS usually follows symptomatic infection by 10-20 days. Of course, we know that individuals may contract the virus up to 2 weeks before they manifest symptoms which is why we are asked to isolate for 2 weeks. Thus, it is remotely possible that the asymptomatic viral infection triggered an immune response that led to GBS much more rapidly than usual.
- One of the factors that predicts severe GBS is a short interval between the inciting event (infection in most cases) and development of weakness. In this reported case the GBS pre-dated symptomatic infection so the interval between viral exposure and weakness must have been extremely short and yet the GBS was very mild with rapid and complete recovery.
- Perhaps most importantly, this is the first case of GBS associated with the virus despite there being more than 1.7 million confirmed cases (as of April 12, 2020) since December 2019 and probably many more that have not been diagnosed. The incidence of GBS is roughly 2 cases for every 100,000 of the population every year so if COVID-19 was a trigger for GBS we would have expected to see about 30 cases, not just this one.
“It is incident to physicians, I am afraid, beyond all other men, to mistake subsequence for consequence.”
Dr Samuel Johnson (1709-1784)
Samuel Johnson made this observation about 300 years ago but it is just as true today and while he made the comment about physicians it is equally true for the entire human race, including those who should know better such as the physicians who wrote the Lancet article. Just because “B” follows “A” it does not mean that “B” was caused by “A”. The authors of the article were quick to acknowledge that this association may just be a coincidence but the headlines generated screamed “First case of GBS associated with COVID-19” which is the message that gets out to the GBS community. We cannot yet say with complete certainty that there is no chance that COVID-19 could trigger GBS but this single case does not change the validity of what I had wrote three weeks ago. As more data emerges we may learn that there is a link but, in the meantime, don’t panic.
Those who wish to read an executive summary of the reported GBS case can access it at: https://www.medscape.com/viewarticle/928424?nlid=134948_3405&src=WNL_mdplsnews_200410_mscpedit_neur&uac=317419EZ&spon=26&impID=2342098&faf=1
The article also provides a link to the original report that was published in Lancet Neurology.