I have hyperpigmentation on my upper lip (it looks like I have a moustache!) that developed after an emergency bowel resection 2 years ago. I have no idea why, but I cam out of surgery with weird dark patches in various places. The ones around the stomach scar went away (mostly) but the patch on my upper lip stayed.
I started using Platinum Skin Care chemical peels and skin care products, and they have helped significantly. It's a bit expensive (around $200 for a full kit, plus I bought the fading cream too) but totally worth it.
I had been using Palmer's fading cream, but it did nothing!