I think the meaning of 'psychosomatic' is actually quite clear-cut, depending on how formally the term is being used, but its meaning sits across a spectrum.
At one end of the spectrum, 'psychosomatic' refers to an illness (with physical manifestations) that is
caused purely by mental factors. (The mental factors are commonly stress, or mental conflict, sometimes associated with personality traits - hence the constant research into personality traits of CFS patients.)
At the other end of the spectrum it can refer to an illness (with physical manifestations, but without a scientifically proven physical cause) that is aggravated or perpetuated by psychological factors.
But it all boils down to the same thing - that the illness is caused, aggravated or perpetuated by maladaptive mental stress or mental conflict (which can be related to personality traits) - and so it can therefore be claimed that it is treatable with psychological interventions.
Whether an illness is said to be either caused, perpetuated or simply aggravated by psychological factors probably doesn't matter too much to those who attempt to classify it as a psychosomatic or functional disorder (except that their theory needs to seem convincing to non-specialist medical staff, and to bureaucratic decision makers.) What matters most is that it can be said that the illness is treatable with psychological interventions.
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The word psychosomatic has had several meanings, including psychogenic, ‘all in the mind’, imaginary and malingering. The modern meaning is that psychosomatic disorders are syndromes in which both physical and psychological factors are likely to be causative."
https://www.inkling.com/read/kumar-...ne-8th/chapter-23/functional-or-psychosomatic
This concept (of a supposed interplay between mind and body) is perpetuated solely by the field of psychiatry, in an attempt to 'own' a number of illnesses (for which the cause is currently unknown) that would otherwise be described as somatic.
Obviously, if the field of psychiatry can 'own' a physical illness (i.e. convince decision makers and the public that psychological interventions - for an apparently physical illness - will successfully treat the illness) then this widens the scope of psychiatry to have more patients, thus increasing the sources revenue. (In the USA, more patients = more money.)
Fundamentally, it's a modern, and more sophisticated (superficially), term for 'hysteria' whereby mental stress, or personality traits, are said to manifest physically.
(The evidence for the lack of actual progress in their thinking is in their assertion that the mind-body dualistic dichotomy is outdated. i.e. This implies that they believe that the power of thought can provoke physical manifestations. And that this happens even in previously healthy individuals. It seems like very old-fashioned witch-doctor type stuff. Even research in depression and other psychiatric disorders is moving away from this paradigm, towards research seeking the biomedical causes. Yes, of course we know there is an interplay between cognition, the brain and the body, but to stretch this to say that individuals suddenly get serious long-term illnesses such as IBS, Fibromyalgia, CFS etc., because of mental conflict, is fantasy. Notice that they never say this for illnesses that have an
obvious measurable physical manifestation - it's only the illnesses that have relatively invisible symptoms - They target the illnesses for which they can just about make their make-believe theories seem plausible.)
In the UK, the term 'psychosomatic' seems to be outdated now, esp in relation to CFS. They prefer to use a
range of other terms (e.g. functional disorder, or functional somatic disorder) which are not so well known to the public and which are not so obviously linked to meaning 'all in the mind' etc.
They know
exactly what they mean in psychiatry, and what they are doing. They've been working on their theories and classifications for decades, spending a lot of time perfecting them and keeping them up-to-date.
In psychiatry, CFS is nicely wrapped up in very specific category (a functional illness) whereby it conveniently is neither a mental illness or a physical illness, but somewhere in between, whereby the symptoms are said to be
both mind and body. (i.e. an unexplained and complex mind-body interplay.) (Note that without the mental aspect of the illness, there would be no interplay, and presumably no illness.) But it all boils down to the same thing - the claim that these illnesses can be treated with psychological or cognitive-behavioural interventions.
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So-called functional (in contrast to ‘organic’) disorders are illnesses in which there is no obvious pathology or anatomical change in an organ and there is a presumed dysfunction of an organ or system."
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...they do not fit easily within either medical or psychiatric classification systems, since they occupy the borderland between them."
https://www.inkling.com/read/kumar-...ne-8th/chapter-23/functional-or-psychosomatic