This could be due to infection, the presence of a foreign body, a tumour, a cyst, trauma, or general inflammation. I would not recommend treatment at home. The area needs to be clipped and closely examined by a veterinarian. If bony involvement is suspected xrays should be taken. If infection is suspected, antibiotics are needed for treatment, and pain medication may be indicated. If cancer is suspected, samples will need to be taken for diagnosis.
