I add also this reference that opened my mind as I really didn't expect it. It's incredible how internet can be resourceful if you can use it well.
"Ileal Pouch Symptoms Do Not Correlate With Inflammation
of the Pouch" https://www.cghjournal.org/article/S1542-3565(13)01432-8/fulltext
"Pouchitis is difficult to define
because, to some degree, all patients have endoscopic
and histologic evidence of chronic inflammation in the
pouch after pelvic pouch surgery. Furthermore, inflam-
mation may be patchy with areas of scattered ulcers with
normal intervening mucosa, or also may include
nonspecific changes such as loss of vascular pattern or
granularity in the absence of frank, acute inflammatory
changes. Likewise, because most patients have histologic
evidence of chronic inflammation, it is believed that only
acute histologic inflammation is specific to pouchitis.
Functional outcomes also vary and may be caused by
factors other than inflammation, such as patient age,
pouch type, pouch size and compliance, anastomotic
diameter, and sphincter tone.
The PDAI and PAS were developed to allow objective
evaluation of the response of pouchitis to a treatment
under study. However, each of these scoring systems also
include clinical symptoms reported by patients. It has
been observed that patients with objective inflammation
in the pouch can have minimal symptoms and vice versa.
This has led to speculation that the contribution of
symptoms evaluated as part of the pouchitis indices are
nonspecific for pouch inflammation itself and may be
owing to other conditions as described earlier. Shen
et al 1 observed that, when using the PDAI criteria, 43%
of symptomatic patients with IPAA had no endoscopic or
histologic evidence of pouch inflammation"