Rare case of rash Spreading on Knuckles

Skin, nail and hair health
1
Hi, A 19 year old boy who is my cousin developed a rash on one of his knuckles around 6 months ago which started as dryness. He has tried many ointments and steroid ointments as well but it is not healing. No diagnosis has been given.

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2

Which ointments has he tried? Has he seen a doctor?Any blood tests? has he seen a dermatologist?