Got mange?

Smokey's got a funny thing going on.  His undercoat hairs are trying to fall out/shed, but only in one spot, on each side.  The guard hairs are fine and shorter there, and you can feel his skin right underneath them, as opposed to somewhere deep under a thick fur blanket.The ground hairs come out in clumps with the brush - but only in these two spots, each side of his hips.  Elsewhere they resist coming out. It gives him a funny, patchy look, like he's got mange.Maybe by the end of summer he will have lightened his coat, just in time to grow it again.  He's such a hot dog in the hot summer, always slinking into the shade and sprawling out.  When HW rousts him out for more walking around, he gives us the aggrieved Must I? Really? gaze.