Let's break this down algorithmically.

Unilateral discharge in a patient >30 years warrants a mammography. Mammography for this patient was normal.

Next step should be to get a prolactin level, but the prompt didn't specify, so let's assume it was normal.

Given a normal mammography and presumed normal prolactin level, physiologic discharge would be the most likely diagnosis.

• Physiologic discharge: Non-spontaneous, non-bloody and minimal discharge with normal physical exam and mammogram
• Pathologic discharge: Unilateral discharge, bloody/serous discharge and/or palpable lump or skin changes

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