Hi!,
Welcome To HealthcareMagic forum,
The condition what you have is called
ACANTHOSIS NIGRICANS(AN) ,in which one has thick and black skin over neck . Knuckles of fingers might also be involved in certain cases.This might be associated with over weight or can be familial.
This is not
fungal infection (in which one would give history of itching).
AN is resistant to treatment and there are very few options .The first being reduction of weight. One should start with
tretinoin cream locally at night over the area ,and a sunscreen in the morning. Also creams like
hydroquinone can help a bit. If this doesn't work then the latest is use of one anti diabetic tablets .For all this you need to consult a good
dermatologist .
regards,
Dr.chawda