Welcome, Ann68!
If you haven't already found this out, you can search here on NeuroTalk for terms or phrases. For instance, when I entered "idiopathic pachymeningitis" in the search window, this is what came up:
https://www.neurotalk.org/search.php?searchid=3602277
And it is listed as a rare disease on the NORD Website:
Idiopathic hypertrophic pachymeningitis - NORD (National Organization for Rare Disorders)