How to monitor state of 50 Digital Inputs Good day.

I have a specific project need and I spent the past couple of days searching on forum, blogs, etc and I'm still not clear if that's feasible to do with Arduino or not.

I need to monitor the state of ~50 digital inputs and trigger an action when any of the pin changes either from 0 to 1 or from 1 to 0, pretty much the same as pin state interrupt works, only difference is that I need to "listen" to ~50 pins, instead of just a couple. I must be able to identify what pin triggered the action and what was the change (0->1 or 1->0).

My initial idea is to use a MEGA 2560 and have a group of 50 "if" statements on the main loop comparing the previous state or each pin (stored in individual variables) with the current one and triggering the corresponding action if something changed.

I'd like to hear from the experts here what would be a more elegant or smarter/faster way to accomplishing this.

I'm eager to receive your feedback.

Thank you.
I had a project that used 16 rotary encoders and I used the MUX Shield which uses 74HC4067 analog multiplexers. They port to A0 - A3 on the shield which is fine as you can set these pins to Digital Inputs else you can get teh breakout version and connect to any input pins.
I also used a Due since ALL pins can be interrupt enabled.
Reading was a bit of a pain but worked like this...
The method is.. Continually address each input in turn in the loop or an interrupt is not detected, when an interrupt fires, address each input in turn again to find out which pin changed state.
Hope that helps.