Repigmentation Occurring Six Months After a Dysplastic Nevus (With Severe Changes) Removed?

I would wait for findings from the second biopsy to see if there is any change in the pigment cells pathologically.  This will allow for a more clear picture of the mole and its recurrence.

It is possible to get a recurrence of a mole, or nevus, after having it excised. The recurrence usually occurs because a root or tiny piece of the original mole is left behind after the excision. Even though a pathologist says the examined margins or borders are clear, they do not typically examine 100% of the margins - just a sample. Therefore, if some of the nevus cells are left behind, they can grow and repopulate the area and appear as new pigmentation within the scar or on the skin. Often, dermatologists recommend re-ecising these recurrent moles to ensure they are completely removed.

When a pathologist reports a mole as a "dysplastic nevus with severe cell changes", the pathologist is basically saying that although the mole appears very atypical, they think the mole is benign. However, to be on the safe side, they recommend treating this lesion as if it were malignant. The treatment recommendation (i.e. excising the mole) is the same as if that mole were a malignant skin cancer. It sounds like your dermatologist has done all of these things.

If your biopsy was read by a board certified dermatopathologist, it would be very unlikely that they incorrectly read your slide as a benign growth (an atypical nevus) instead of a malignant growth. Recurrences are uncommon after an excision with clear margins but can occasionally occur as the pathologist cannot see all of the margins on the slides. A simple re-excision is all that is usually necessary. That is why it is so important for patients to return for their follow up examinations to recheck the surgical site and have the remainder of their moles checked routinely.