This in no way a professional opinion...just a loving per owners! (just to clarify)

It MAY be something as simple as an allergy.

My dog Biggles (Cairn) has a few allergies, and before we knew this he used to lick his front paws excessively and pull the hair out, he also chased his tail and used to try and scratch his back on our pebble dashed garage.

Just a though... dog allergies can include :

Fleas

Atopic Dermatitis - caused by the dog’s immune system hypersensitivity to common substance around them, such as dust mites or mold

Bacterial Allergies - Bacterial allergies will cause hair loss that looks similar to ring worm. The areas that are infected need to be treated with antibiotics.

Inhalants (tree, grass, weed, dust mites, molds, and chemicals)

Food (fish, eggs, whey, milk, chicken, pork, beef, corn, wheat, soy products, chemical preservatives, and artificial sugars in their meal)

Food is the least common type of allergies in dogs. Some of the common items that may cause a reaction are wood bedding, grass, plants, and flea collars.

You might want to check out this page as it will give you more information...

The best thing you can do, it keep a diary of everything you Staffie does, everything he eats, absolutely everything you notice about him. Usually something that you wouldn't even think about can be the key to an allergy.

I hope you lil one gets back to his full coated self!

It always seems scary when there's something wrong with your dog, but if you can get it sorted your staffie will thank you for it!!