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No, not likely. At 18 yrs old the immune system is not what it used to be, most likely you are dealing with bacterial folliculitus (much like acne) and the bumps and bleeding is from that. Clean the area with phisoderm and apply benzoyl peroxide.
I recommend getting bloodwork to see why the weight loss, many times if there is a compromise in kidney or liver, a switch of food can help.
If your vet thinks they are other types of lesions...they can see them...I cant.
I recommend that you stagger with the ointment and then a hydrocortisone cream...to help with inflammation.