This month's musings were prompted by an old friend of mine telling me he had been diagnosed with Charles Bonnet syndrome, possibly as a consequence of a small stroke affecting his visual cortex. I regret to say that I was unaware of this particular malady (a depressingly frequent occurrence as time marches on) so I consulted that modern equivalent of the Oracle of Delphi that is Google.

As so often happens, a simple query such as this leads one down a path of enquiry that is exceedingly fascinating, and Msr. Bonnet turns out to be almost as fascinating a polymath as James Parkinson, of whom I wrote in a previous post. Born in France but spending most of his life in Geneva he was, by profession a lawyer but that particular profession was not to his liking and so he devoted most of his life to the study of natural science. In 1740 he was the first to describe the phenomenon of parthenogenesis in insects and he also identified the mechanism of respiration in insects via spiracles or cutaneous breathing tubes. Such was the regard in which he was held that in 1743 he was elected to the Royal Society at the tender age of 23.

In 1760 he described the condition which now bears his name after observing the characteristic symptoms in his grandfather, who had severe cataracts. Despite being almost completely blind, he described seeing peoples, animals and birds and other objects. The syndrome is characterised, as in his grandfather's case, by vivid visual hallucinations in people who are psychologically completely normal. The condition is commonest in the elderly with visual impairment and consists of seeing spurious images, often in low light conditions and also frequently quite complex. Needless to say, people with this syndrome are often extremely distressed, fearing that they are going mad and sometimes hiding the problem from their families or medical advisers. The condition can improve over time and various strategies can assist in ameliorating the effects, but often knowing that this is a visual rather than a psychiatric issue is sufficient to reassure.

Reading of Msr. Bonnet's syndrome then led me to think of the various instances in which hallucinations are a major feature. We all know of the significant and distressing hallucinations that can accompany psychotic illnesses and the terrible consequences they can inflict. However, I was unaware how the hallucinations of psychosis are shaped by the world around us and the society in which we live. In earlier times hallucinations were often of a religious nature with sufferers hearing the voice of a god or saint. In more recent times more secular features emerged: people thought they were being controlled by foreign agents and the like. Now my psychiatrist friends tell me that aliens or spacemen are frequently described. The main thing about hallucinations is the distress they cause to the sufferer, their friends, and families.

In our own area of pharmacovigilance hallucinations are relatively uncommon, but there are a large number of medications that have been associated with such phenomena, and not only those with psychoactive properties. Still, we can highlight some correlation between Pharmacovigilance and Charles Bonnet syndrome: Adverse reactions have the potential to be misunderstood by the patient, and subsequent events such fear can be a driving factor in withheld information or delayed reporting.