I'm sorry to hear that Oscar has had several medical issues recently.
With regards ***** ***** this is likely the cause of the fur loss. This is an important point as fur loss without scratching tends to be hormonal in older dogs.
Can I assume that this is a new thing for him i.e. he didn't suffer with itchiness or allergies when younger? If so, an allergy would be extremely unlikely at this age, unless you have started to do something dramatically differently e.g. offering a new food with ingredients he has never tasted or completely changing his environment.
The first thing to consider would be a parasitic cause. Fleas, mites etc. are not just found on pups and in fact are commonly found on older dogs, especially those that have been unwell. These can cause intense itchiness and fur loss and are not always visible to the naked eye. It is worth ensuring he is up to date with a strong preventative, such as Advocate, Prinovox or Nexgard Spectrum. There is also the option for the vet to perform a deep skin scrape in the affected areas to check for parasites under the microscope.
We would want to ensure there is no underlying cause for the itchiness on the head, such as a grumbling ear infection, dry eyes or dental disease. Any of these things in an older dog could potentially cause rubbing.itching and then fur loss. Examine the ear canals for a small or discharge and ensure the eyes themselves are clear and moist, with no ocular discharge. Look inside the mouth and ensure the teeth are white and clean with pink gums, rather than caked in brown/green calculus with red angry gums and a bad smell.
There are a number of other causes of fur loss and itchiness, including bacterial and yeast infections. These could be confirmed with a swab and may require a medicated wash and/or oral tablets to clear up. Again, those that are older and have been unwell would be more prone to them.
If none of the above gets us a solution, I would suggest a general blood test to check for any underlying medical issues (checking kidney/liver function, white cell count etc) as well as a thyroid hormone check; to ensure it is not under-active.
To protect the skin while he is itchy, use a buster collar to prevent further self-trauma.
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