Can episodic variety clusters change to chronic?

Hi Everyone.

I just joined OUCH to help in supporting my boyfriend who has suffered from episodic cluster headaches for about 20 years.

He's been in the throes of an episode that has gone on much longer than his usual bouts. At this point, he's worried that they'll never end. Is it common for episodes to vary in length and severity? Is it possible or common for clusters to switch from episodic to chronic variety?

I did a general search (I'll admit, probably not very thorough). If the information is on the site somewhere, please point me to it; I'll happily read. :)

Thank you,

Cathy