Hi there
Has he ever experienced anything like this before? I am going to give you the link to our Diabetes site where they may be more familiar with diabetes symptoms.
The American Diabetes Association provides a fairly comprehensive list of diabetes skin complications.
Since it is spreading and there is swelling involved I would call your dad's doctor right away. You probably don't want to wait on this.
I hope he feels better soon. Let us know what happens if you can.
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