Dr Philip Welsby muses on the perils of trying to assess one’s own signs in the mirror…
There was an interesting paper in the Journal of the Edinburgh Royal College of Physicians in which Stefan Slater detailed his Bell’s palsy.1 He was surprised to learn that, contrary to his experience, many revered authors stated that it was the paralyzed cheek that could not be puffed out. Often neurological appearances are produced by the unopposed actions of normally innervated and thus normally functioning muscles. For example in a third nerve palsy the eye looks down and out because of the unopposed action of the fourth (superior oblique) and sixth nerve (lateral rectus) innervated muscles.
In line with this thinking, Dr Slater’s observation on his left-sided Bell’s palsy is obviously correct. The seventh nerve innervated buccinator muscle on his right was fully functioning and helped push air into the left cheek whose expansion was unchecked by his paralyzed left buccinator. Having said this, perhaps the revered authorities were correct because with a left Bell’s palsy the left cheek often did not puff out because there was leakage from the left side of the mouth, closure of which is mediated by the seventh nerve.
I initially, and wrongly, thought that Dr Slater might have fallen into the “van Gogh trap” in which people who self-observe themselves in a mirror do not realise that the mirror image is a mirage (there is no one behind the mirror) and thus mirror images do not reflect reality. Notably, the left hand becomes the right hand of the viewer’s mirror image. I wonder how many of the revered authors had a Bell’s palsy and looked at themselves in the mirror (van Gogh, who was right-handed, cut off his left ear but his self-portrait shows a bandaged right ear – he had obviously painted himself using a mirror2). I recall a telephone conversation with an HIV positive patient who had developed a Bell’s palsy and was totally confused until I realized that he knew he had a right facial problem but was describing some manifestations on the left as possessed by his mirror image.
1. Slater S. My cheek puff sign: Bell’s palsy, Charles Bell and Dr Robert Knox. J R Coll Physicians Edinb 2021:51:246-9
Philip Welsby is a retired consultant in Infectious Diseases based in Edinburgh. He is an Assistant Editor of the Postgraduate Medical Journal.
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