ispell-format-word

ispell-format-word is a variable defined in `ispell.el'.
Its value is

upcase

• This variable is an alias for `ispell-format-word-function'.
• This variable may be risky if used as a file-local variable.

Documentation:
Formatting function for displaying word being spell checked.
The function must take one string argument and return a string.

You can customize this variable.