Florence Foster Jenkins and Self Delusion

L and E took me to see Florence Foster Jenkins for Mother's Day.  I thought it was a comedy, but came out in a very reflective mood.
Florence Foster Jenkins was a very wealthy woman who lived in a hotel in New York and patronised the classical music scene.  The film explores the last few years of her life, in the 1940's, when she was in her 70's and very ill.  Her illness, however, was not made much of in the movie.
She had a passion to sing on stage, and despite the fact that she couldn't sing a note in tune, persisted with her efforts, taking on the most difficult of coloratura soprano arias, until finally hiring Carnegie Hall and singing to 3000 people.
It was at Carnegie Hall that the 'but the Emperor has no clothes' moment finally arrived.  It was, apparently, the first public concert she gave, all previous concerts had been by invitation only, and therefore excluded music critics.  This time, a music critic from the New York Times attended, and spared nothing in his review.
FFJ not only loved to sing, but believed that she had true talent.  She appreciated other opera singers, such as Lily Pons, and had trained as a classical pianist, so it's interesting to wonder why or how she failed to hear how tragically bad her own singing was.
The illness she had was syphilis, and herein lies the clue as to her remarkable self delusion.  She had had it for forty years, in fact, and was into the third stage, and treating herself with mercury and arsenic.
I haven't thought about syphilis for a long time.  It's one of those illnesses which has receded into the past, thanks to the advent of antibiotics.  An STD with initially relatively mild symptoms, it emerges like a monster in a horror movie after decades, attacking the brain and nervous system.  Degeneration into madness is relentless, and death inevitable.
I remember a number of patients in the back wards of the old psychiatric hospital I worked in in the 70's who had end stage syphilis.  It was called dementia paresis, and was not pretty.  One of the very characteristic symptoms was delusions of grandeur.  Patients would think they were members of the Royal family, or that they were immensely wealthy, or that the plastic beads around their neck were diamonds.  They would believe themselves adored and admired, and saw themselves as dispensing largesse to everyone around.  (FFJ gives 1000 tickets for her Carnegie Hall concert to war veterans - a very typical gesture.)  They would think they were beautiful, when in reality their faces were ravaged by their illness.
It is plain to me that FFJ's belief that she could sing opera was a symptom of her illness.  It was a pathological delusion.  Had it not been for the protection afforded her by her actual wealth and an apparently doting husband/partner, she no doubt would have been incarcerated in an asylum like so many others were.
Much of the tension in the movie comes from the elaborate and sustained effort by those around FFJ to collude in the pretence that she can sing.  They support her delusion, encourage it.  Anything that threatens to confront it is smoothed over, blocked, or explained away.  Everyone around her tells lies, big and small, in order to support the central, grotesque delusion.
The rationale for this is that 'we love her.'  Also, there was the unspoken threat of financial support being withdrawn if anyone ever confronted FFJ with the truth.
Self delusion of course  can exist without an obvious underlying medical cause like syphilis, although the clarity and totality and distinctness of it's manifestation in third stage syphilis makes me think that all forms of self delusion may have a pathological cause, albeit unknown.
Sometimes people may believe that they are doing a good job, when in reality they're performing poorly.  People may think they are the most amusing person in the room, whereas in fact everyone is bored witless by them.  Someone's conviction that they are right about something may resist all evidence to the contrary and all efforts to convince them that they're not. 
I wonder if being deluded about yourself is similar to having a false body image, for example, an anorexic who actually weighs five stone, may have an unshakeable conviction that they are overweight.  Could it be some actual neuronal trick of the brain that makes us have a perception of ourselves that doesn't accord with reality?
We used to be taught in psychiatric nursing that the right way to respond to a patient's delusions was basically, 'I understand that you believe X, but in fact that is not true.'  It's the opposite approach of course, from the way the people around FFJ treated her.  Their failure to reflect the truth about her exposed her to ridicule and notoriety, although she was apparently blissfully unaware of this.  She collapsed and died very shortly after reading the NYT critic's review.
It is of course the nature of delusions to make you blind.  How can you even know you have one if no one tells you?