While hyperadrenocorticism would probably be the number one differential diagnosis in dogs with classic clinical signs—pot belly, bilateral symmetric alopecia, polyuria, and polydipsia—this diagnosis may be overlooked in patients with more subtle clinical signs. Cushing's syndrome can be challenging to identify because of its variable clinical manifestations in our canine patients. One of the trickier clinical presentations for veterinarians to keep in mind is recurring pyoderma.
In our practice, we find that some patients with hyperadrenocorticism experience recurring skin infections, but show none of the classic physical findings usually associated with cushing's syndrome. Instead, the only visible manifestation of cushing's disease is their recurring skin infections (Figure 1).
Figure 1. A dog with pituitary-dependent hyperadrenocorticism and secondary mucocutaneous pyoderma.
Remember pyoderma causes
Superficial staphylococcal skin infections or superficial pyodermas are common in dogs and have many different underlying causes. However, these underlying causes can be separated into two major categories: allergy and endocrinopathy. The patient's age can be a diagnostic clue since many allergic dogs will initially be presented at a younger age, whereas dogs with an endocrinopathy, such as hyperadrenocorticism or hypothyroidism, will be middle-aged or older when their infections develop.
For patients that were confirmed to have and were treated for superficial pyoderma that resolved but then recurred, veterinarians should try to accomplish two goals: 1) address any active infection more intensively with topical products, and 2) identify and treat the underlying cause of the infection.
Address pyoderma topically
Because there has been a dramatic worldwide increase in the incidence of methicillin-resistant Staphylococcus pseudintermedius (MRSP) skin infections in dogs during the past five years (Figure 2),1-3 it may no longer be appropriate or acceptable to simply repeatedly treat such patients with systemic antibiotics. In my experience, topical chlorhexidine works well in patients with superficial bacterial skin infections. I have found that one of the more effective topical antimicrobial formulations to add to my pyoderma therapy regimen is 4% chlorhexidine combined with TrisEDTA (TrizCHLOR™ 4 – Dechra Veterinary Products). TrizCHLOR 4 is available in shampoo, spray-on, and medicated wipe formulations, and is indicated for support of healthy skin in animals with conditions responsive to chlorhexidine. In my practice, addressing an active superficial pyoderma topically with TrizCHLOR™ 4 may help resolve the infection without the use of systemic antibiotics, if the patient can be bathed several times a week and the infected area is sprayed twice daily. I also use these topicals to help reduce the recurrence of infection until the underlying cause can be identified and controlled.
Figure 2. Dorsal trunk of a bulldog with a large plaque of calcinosis cutis and draining furuncles caused by methicillin-resistant Staphylococcus pseudintermedius superficial and deep skin infection due to pituitary-dependent hyperadrenocorticism.