A Diophantine equation

What is in general known about positive integer solutions (x,y) with x and y different of the equation x^4 + m x^2y^2 + y^4 = a square, for m an integer?

There are of course easy cases (such as m=+-2).

And there are known to me special cases (not easy) such that m=-1 (SIERPINSKY?) where the equation has no such solutions.

Kent Holing
NORWAY

.