Anosognosia has long been associated with neurological disorders, e.g., dementia, but in recent years some mental health advocates have seized on it as a justiification for expanding involuntary psychiatric treatment. They portray it as a clinical feature of serious mental illness rather than a lack of information about the nature of a particular illness that can be addressed through psychoeducation. Is there any evidence that anosognosia affects individuals with mental illness?
Well you could look up Xavier Amador and Tony David's book on the subject, Insight and Psychosis, OUP 2004, 2nd edition as a starting point for a considerable literature stretching back into the 19th century, at the least. It's a pretty complex field.
I'd argue that the short answer is yes, there is a lot of reason to believe that poor insight is a core feature of psychosis, and that lack of insight into having an illness (or disorder or whatever term one thinks best) is a common feature beyond the lack of insight into symptoms that is necessarily present in psychosis.
A colleague (Richard Bentall) says that poor insight is having a different theory than your psychiatrist, but I'd argue that it's having a different theory than your psychiatrist could reasonably expect you to have. In that sense it's significant of pathology. There is some evidence that the poor insight with which people with schizophrenia present is due to poor metacognition, or the ability to understand how well one is performing cognitively - Daniel Koren published a paper in 2004 showing this and this sort of view informs much of Paul Lysaker's research (and his book). I have as yet unpublished data consistent with this. There is also meta-analytic evidence linking poor insight to other cognitive deficits, e.g. executive function. It is worse in people with more severe psychotic symptoms. Psychoeducation often has very limited effect, or psychiatric treatment would be a whole lot simpler.
This is all a simplification of course but the complexity conceals a stark truth: psychosis erodes one's judgement in a unique manner and compulsory treatment to allow some sufferers to recover enough to make their own meaningful and authentic decisions is something society should value, or if you like, a right.
Agree with RJD above.
While poor insight (PI) is considered a hallmark of psychosis, a good contrast to study is obsessive-compulsive disorder, in which good insight into the irrationality of symptoms was the basis for diagnosis, for many years, until the DSM IV recommended after a field trial that a substantial proportion of people with OCD also have poor insight.
Research over the past few decades has indicated specific clinical characteristics linked with PI in OCD, which is independent of simply more severe symptoms. And psychoeducation in this disorder is presented often to the individual from multiple sources (e.g., family, treating team) and is intuitively known to the individual too. Multiple symptoms being common in OCD, individuals often have good insight into many symptoms, but may hold certain beliefs with rather more conviction. We recently studied neuropsychological mechanisms that might underlie PI - why these individuals might hold such irrational beliefs despite encountering much evidence to the contrary. Based on the significant neuropsychological findings, we proposed a model that perhaps individuals with PI may have difficulty in processing information contradicting their own beliefs due to conflict resolution deficits; memory deficits may prevent them from updating their belief systems with the corrective information from psychoeducation; and owing to difficulties in organisation and associative exploration they may be unable to access this information which may actually exist in memory. This of course is only one way of looking at it.
There is also some interesting research on neural correlates of beliefs and self reflection in normal individuals, and neuropsychological and imaging studies (Aigner et al, 2005) in PI OCD have suggested similar deficits. I'm attaching some papers which might be of interest. What would be intriguing is what happens within the brain as insight improves as well. Look forward to others' thoughts.