It could easily be that the underlying disease impairs patients ability to handle stress or responsibilities of daily living so that they do indeed experience more psychological stress.
It could also be that having a disease like this, which is stressful enough in and of itself, but which is also treated very shabbily by society, is enough to explain any stress related symptoms patients are exhibiting.
I, for one, certainly don't deny having huge stress loads to deal with, and its appalling consequences, especially after more than 30 years of it.
But that doesn't mean stress has a primary causal role (predisposing, precipitating, or perpetuating, to use the stress-ophiles jargon), or that superficial psycho-behavioural therapies are of any substantial value in relieving it.