Hello I am Dr. Joey. Thanks for trusting me to help you and your pet today. I am a licensed veterinarian with over 15 years of experience. I look forward to working with you. I also apologize for the delay in having an expert get back to you.
The most common cause for recurrent sores on the paws, if on the skin (not the pads; and clarify for me if you are speaking of pad lesions because that is a different discussion) is chronic allergic skin disease. The conformation of the pad and accumluation of dirt is probably secondary to the fact there are sores that keep the area moist and sticky. This accumulation of debris is usually NOT the primary cause. It is, however, important to cleanse the paws regularly and be sure any time he comes indoors to have a towel by the door to wipe off all debris. This can help prevent infection tremendously.
There are several primary allergies that can lead to itchy paws, the secondary infection (and hence sores) which include food allergy dermatitis, atopic dermatitis (environmental allergy), contact dermatitis or flea allergy dermatitis. It is unlikely to be the latter two. What happens is the allergy leads to inflamed and itchy paws which Juno would then lick, creating a perfect moist environment for a secondary bacteria, yeast or mite infection to set in. This problem can be chronic and very frustrating! To clear this long-term requires working with your vet to treat the paws when they flare up and search out the underlying allergy. It is also very important at his age to screen him for an underlying endocrine disease such as hypothyroidism (underactive thyroid) or Cushing's syndrome which would contribute to the allergies and predisposition to skin infections.
So, what can you do at home? The most common infection we see on the paws is either bacterial or yeast. You could start doing paw baths in a good shampoo that would treat both of these issues such as Malaseb (you might need to get this from your vet or ask your vet to prescribe a good multi-functional shampoo). When you do this bath, you will not have him in standing water, but get the paws wet, work the shampoo into the skin/paws and then let stand for 5 to 10 minutes before rinse and towel dry. Over-the-counter you could try an antidandruff shampoo for people such as one with the active ingredient: selenium sulfide (this will help if the problem is bacterial). If you are sure this is a recurrent yeast problem then you can look for a people antidandruff shampoo that has ketoconazole in it. There is often one of the shelf. You may use an antihistamine such as diphenhydramine (dose is 1mg per pound every 12 hours) to help with itching but this is not that effective (only helps about 25-30%); a corticosteroid from your vet will be more effective.
In an ideal situation you need to have your vet take a look and then do a skin scraping for evaluation under the microscope -- looking for not just mites but also bacteria and yeast. Then appropriate medication can be prescribed to clear this. However, as I mentioned before this can be recurrent and frustrating. If you are already in this recurrent state, then you need to work with your vet to determine what underlying allergy is present. This usually involves first an 8-12 week hypoallergenic food trial using a prescription medication from your vet with specific/limited ingredients. It is not as simple as switching brands since most food allergic dogs are allergic to a protein (not grains; that is a marketing ploy) such as chicken or beef or lamb or milk. If you already know this is not a food allergy, then the step after this is to consider either allergy testing (serum which is via blood or intradermal) and then allergy shots to densensitize him to what he is allergic to OR considering a longer-term drug such as cyclosporine or the new Apoquel when it becomes available.
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