I am 23 years old female. I have a new black hyperpigmentation on my right thumb metacarpophalangeal joint. I do not have history of trauma, uv radiation exposure, or extremes sun exposure. It is around 6 mm in diameter with irregular color. Border is not clear. It has been there since a week or longer. I'm hoping that it's not malignant melanoma. Im a 4th years mbbs student so my half knowledge makes me panic for the smallest of things. Please tell me this is not one of them and what I could do about it?