Debbie,
I don't have much concrete news. Since the tingling, my wife stopped Humira in order to "remove it from the equation." She had an MRI at a neurosurgeon's suggestion and the results showed no lesions or damage to her brain (I'm sure your PCP will suggest this too). He had no conclusive information to share, but felt that Humira was not DIRECTLY causing the tingling. While he did not committ to any one cause, he suggested that because Crohn's and MS share some traits and there is much still unknown about the two, there could be some link between the tingling and the Crohn's.
The other potential cause suggested was that the Humira indirectly brought on the tingling in her hands and legs. We already knew the Humira caused extreme fatigue and soreness, so the theory is that an already tired and stressed person who then took the Humira injection became even more fatigued and this brought on the tingling and headaches.
Since the MRI, the tingling has subsided for whatever reasons. The bottom line for my wife was that the Humira didn't really work well, was expensive, and indirectly caused the tingling. So, we're probably done with it permanently and at least for now. She has a checkup with the neurosurgeon in 2 months and if there's no further symptoms including headaches I'd suspect we're done with this episode for now. As the neurosurgeon said, it's hard to diagnose the causes for much of what he deals with. I'll keep this post open though and respond if there is an update.