Do you have fordyce spots on your lips? A lot of people on the forum seem to report that they have fordyce spots on the lips.
Lips don't usually have oil glands but fordyce spots are sebaceous glands in an abnormal position.
Fordyce granules are sebaceous glands that are located in the vermilion zone of the lips and the oral mucosa. Historically, these sebaceous glands have been considered ectopic[MEANING: they don't belong there]; however, because they are such a common clinical finding in the oral cavity, Fordyce granules should be regarded as a variation of normal anatomy. They can also be found on the vulva.
Fordyce granules are found in both sexes and are less common in children. The prevalence of Fordyce granules ranges from 70% to 84% of the population. "
So it could be that people with EC experience something akin to Sebhorric dermatitis on the lips because, unlike a large percentage of the population, we do actually have a large percentage of oil glands on the lips? So the sebum is a medium for fungal proliferation?
I still think EC is connected to dry mouth but this is another possible answer.
Regarding your question about hyperkeratosis, yes accutane is a traditional treatment for hyperkeratosis disorders (like harlequin type ichthyosis). However, I think with EC the hyperkeratosis is a protective mechanism occurring in response to chronic inflammation.
So I think it's really important to try to figure out what is causing the lip inflammation, rather than just trying to treat the hyperkeratosis.
In other words, in some disorders like harlequin type ichthyosis, there is a genetic abnormality that produces hyperkeratosis. So it makes sense to target the hyperkeratosis as the root cause of the disease process. However, with EC the hyperkeratosis seems to be secondary to chronic inflammation of the lips.
What is the source of the ongoing inflammation in EC. It is unclear. Is it dry mouth? Is it autoimmunity? Is it fungal or bacterial infection? Is it an allergy? Is it self induced trauma (are people rubbing their lips a lot)?
But you could try accutane if you feel comfortable with it since it is recommended for hyperkeratosis.
I think I would try topical tacrolimus first (protopic ) if you haven't already tried that since it is recommended for both EC and Seb derm and has less side effects.