corrupt index with optimize but not corrupt with check or analyse

I work with a table with 20 million rows. I have tried to Optimized this table, but SQL return me:

• "Index for table '<table_name>' is corrupt; try to repair it"

But if I do a analyse on this table. SQL return me

• 'OK'.

So my question is: there is a issue with the size of my table which prevents the optimize? Or the problem is elsewhere ?

edit:

OPTIMIZE TABLE <table_name>
note    Table does not support optimize, doing recreate + analyze instead
error   Index for table <table_name> is corrupt; try to repair it
status  Operation failed


ANALYZE TABLE <table_name>
status  OK