Hyperpigmentation after picosure focus even with strict compliance of tretinoin at night and sunscreen in the morning!

Got a 3 tx of picosure focus for an atrophic scar in my face,this scar is quite disfigured due to repeated cystic acne on the same spot.The scar is quite deep with dark & somewhat bumpy/raised, irregular borders.after 3 tx,the borders are still dark!How could this be i thought pico can lighten scars?I was thinking the borders might be hypertrophic scars & doesnt really benefit from a picosure.The depressed area did somehow effaced. The borders are now my problem since they are very visible/dark.

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