Nothing to worry about at all. Pseudobulbs will shrink and wrinkle with age, especially as new growth appears (they're transferring nutrients into the new growth). They'll even shrink during a long blooming period where they've been sustaining the flowers for a while. I've even seen the PBs of some types get almost totally dessicated-looking, as if they weren't getting any water or their roots were rotten. A quick unpotting showed that that wasn't the case, so the behavior seemed to be just typical for the type.
Just make sure you're watering regularly for your conditions and growth medium, and that the medium isn't soggy....