I have the same problem of debilitating spasms.
I found the cure by accident .
I figured spasms can be connected to electrlytes so I took some Potassium pills my doctor had perscribed a while ago. So I took one and 2 aleeve n like magic spasms gone. Potassium Hcl ER 20meq..ask yur doctor. Dont know why it works but it does. 20meq = 1500mg but its extended release. Iv been on Imbruvica for 4 months. Except for the daily bloody nose n spasms (now sussed out) it seems to work.