BTG3 and cyclic hematopoiesis: The profile of serum kynurenine metabolites in patients affected by CH was similar to that reported in the accompanying manuscript in patients with chronic migraine with two notable exceptions: (i) XA levels, which were decreased in patients with CH, but increased in patients with chronic migraine; and, (ii) ANA levels, which were increased to a much lower extent in patients with CH than in patients with chronic migraine.