How can I solve this equation under one constrain?

I want to solve the following equation:

eqn = (A - B)/(q*(A - B)^2 + 1) + (q*A^3 - 2*q*A^2*B + q*A*B^2 + A)/((A - B)*(q*(A - B)^2 + 1)) - (2*q*(A - B)*(q*A^3 - 2*q*A^2*B + q*A*B^2 + A))/(q*(A - B)^2 + 1)^2 - 1 == 0;

for B (or A which ever is possible) under two separate constrains. Once using constrain

B > A

and then using constrain

A > B

How can I do that in Matlab?