The effect of magnetic islands on the propagation of lower hybrid waves is investigated analytically for a model slab equilibrium with a single helical perturbation corresponding to an m=1 or m=2 island. From the variation of k∥ inside the island, the parallel current is estimated with the same pitch as the original perturbation. The effect of such a current on the nonlinear evolution of an m=2 island corresponds to a destabilization of the mode if the rf driven current is in the same direction as the global parallel current. A comparison with numerical solutions of the problem using a toroidal ray trajectory code is also presented.