Skin hyperpigmentation due to unknown inflammatory process?

What does a finding of post inflammatory of skin  mean if there was no inflammation at the site of the hyperpigmentation and its diffuse in multiple locations?

[Srfr_10]

        I'm wondering the same thing.  I have a large hyperpigmentation on my arm that has only been diagnosed as post inflammatory hyperpigmentation.  Yet there seems to be no known cause or trauma that would have lead to the inflammation.  The spot appeared about 2 years ago, looking like a faint bruise and now it is larger than the size of a quarter and is a dark brown/red.  
        Every so often, about 2-3 times a year, the spot will get inflammed, dark red, itchy and swollen for a couple of days. Again, I don't know what would be provoking this.  
        I've been to a couple dermatologists who have no answers and just prescribe bleaching cream (which hasn't really helped either). I'd like to know if anyone has experienced this as well or has any insight/theories for me. Thanks!