skin condition in 12 year old German Shepherd

Question
Hi, my 12 year old GSD has developed a skin condition recently. I have been reading up on Hot Spots and it sounds similar but some of the symptoms don't add up.
The main area is on his back, starting from the mid back, down to the tail. There are wet puss filled areas that spread like wild fire. He doesn't have fleas or any other visible bugs. His hair is fallen out in these patches and has thinned massively all over his body. It's non itchy, or maybe he's too old to reach it. He's generally well in himself and is eating and drinking normally. These areas seem to scab over, although under the scabbing it seems there is hard, almost calcified white stuff deep in the skin. Like hardened puss. He's never had this before and i haven't changed his diet etc so don't think this a cause. The only other site of injury on him is a bed sore on his elbow which sometimes flares up.

I hope you can offer advice as the vet has put him on very expensive antibiotics that don't seem to be doing much.

I don't know if to bath him, or keep him dry.

Look forward to hearing from you.

Joanne

Answer
This is most likely an allergy to something causing a severe inflammatory reaction. The skin that thickens can be softened and removed with an anti-seborrheic shampoo.  If the vet has not used any steroids in your dog, ask if that can be done.  That will slow down the excessive reaction of the skin to whatever is causing the thickening and oozing of the skin.