A perfect electromagnetic conductor (PEMC) gives rise to a new type of boundary. However, as an actual medium, the PEMC should be considered as a limit of a more general class of Tellegen media which has been called Minkowskian isotropic media (MIM). Actually, a MIM is the most general medium that is isotropic for the whole class of inertial observers, i.e., its isotropy is an ob-server-independent characterization in Minkowskian spacetime. The most important feature of MIM is that it enables a unique and well-defined electromagnetic field in the interior of a PEMC – as oppose to other research approaches previously published in the literature. In this work, follow-ing that new unified MIM/PEMC approach, the guided electromagnetic wave propagation in a symmetric slab containing MIM layers is developed. The main goal is to show how the special case where the MIM layers reduce to PEMC layers can be easily handled, leading to dispersion equations with nontrivial electromagnetic field profiles in the regions filled with a PEMC as the corresponding solutions.