Skin disease - A 12-year-old dog has both backsides hairless and an ear haematoma 1/2

Around the last 4 weeks, this old cross-bred started losing hairs in his backsides including the tail. The causes are varied for this bilateral alopecia. It could be due to hormonal, tick bite/powder allergies, anal sacculitis, ear infections and injuries. Ringworm was diagnosed by Vet 1 and there is ringworm. However, this skin disease is due to a few causes.

It is uncommon to see a case similar to the bilateral endocrine alopecia in cats and dogs or "flea bite dermatitis" in cats.

Could this be a case of sex hormone dermotosis or just anal sacculitis? This is a case where there are more than one cause of skin itchiness. The causes include anal sac infection, ringworm infection and possible tick bite allergy.