Canine pyoderma is a common disease. Its treatment is becoming more difficult due to the emergence of methicillin resistant Staphylococcus pseudintermedius in dogs. The key to success is to treat the pyoderma successfully with the correct antibiotic and topical therapy. Key diagnostic tests include cytology, and when indicated, culture and sensitivity. To prevent recurrence requires identification and management of the underlying cause.

Dane Disaster: How Can We Help Georgia?

Georgia is a 9-year female spayed Great Dane with recurrent deep infections previously responsive to cephalexin. She was diagnosed with hypothyroidism 2 years prior to referral and placed on thyroid supplementation; however, the owner stopped the thyroid medication 3 weeks later because the dog became very itchy. Since that time, she had taken several courses of cephalexin with diminishing response. Her itch level was considered mild (3 out of 10).

Physical examination showed a lethargic dog with extensive and generalized seborrheic skin changes, alopecia, and a dull brittle coat. Erythema and crusting was generalized ventrally, and there was extensive callus formation in her intermandibular space and on her pressure points, associated with deep infection. Given that her total T4 levels 2 years previously were measured at 0.2 microgram/dl (with normal greater than 1), we hypothesized that the persistence of her pyoderma was due to hypothyroidism. But the lack of response to cephalexin in spite of correct dosing for several weeks led to our suspicion that this dog had developed a methicillin resistant staphylococcal infection.

Our initial workup consisted of skin scrapings to rule out the possibility of demodicosis and they were negative. Our cytologies showed 4+ cocci and 4+ Malassezia yeast. We collected material for culture and sensitivity using a sterile culturette moistened with sterile saline. Three different areas underlying crusts were swabbed for the sample. We also drew blood for total T4 and free T4 by equilibrium dialysis. We started oral therapy with 300 mg ketoconazole daily for the yeast and recommended bathing every other day with chlorhexidine and miconazole shampoo (Malaseb, DVM, Bayer) until the culture and sensitivity results were available.

Five days later we received the culture and sensitivity results, as well as the thyroid test results. Georgia was infected with a methicillin resistant, multi-drug resistant Staphylococcus pseudintermedius sensitive only to amikacin, rifampin, and mupirocin. Her total T4 measured 0.1 microgram/dl (normal greater than 1) and her free T4 was 0.2 microgram/dl (normal greater than 0.7); these values confirmed our clinical assessment of hypothyroidism.

The bathing had helped reduce her infection but because her pyoderma was deep, we chose to use oral rifampin 5 mg/kg once daily and we continued bathing 3x per week. We also asked the owner to apply mupirocin ointment topically twice daily to the callus areas under her chin and on her elbows. We wanted to start thyroid treatment as well, but the owner was concerned about the previous increase in itch. The itch could have been due to a number of factors, including unresolved bacterial and yeast infections. We also considered that her hypothyroid state could have been masking the itch of atopic dermatitis. However, she had been taking Soloxine brand of L-thyroxine and we have observed that some dogs will show increased itch associated with the dye in these tablets. We therefore chose to use the dye-free 0.5 mg tablets, giving 1½ tablets twice daily.

In two weeks, the pyoderma was approximately 70% resolved, and the dog appeared to be tolerating the rifampin well (ALT and SAP were normal). We continued our therapy and planned to recheck her in an additional 2 weeks. Two weeks later, the pyoderma was 90% improved but her ALT levels were elevated and the owner reported that she was not eating as well. We therefore stopped the rifampin, but we continued bathing twice weekly and we continued the topical mupirocin. Two weeks later, the pyoderma was completely resolved, and Georgia was looking and feeling quite a bit brighter. We took blood 6 hrs after her morning thyroid medication to check her T4 levels and they were 2.5 microgram/dl, well within the normal range of 1–4.5. We stopped the mupirocin but continued bathing weekly to every other week and planned to see her in about 3 months. At that time, her coat and skin were normal and over the 3 years we followed her, she did not relapse with pyoderma again.

Important Points

1.  Hypothyroidism is one of the potential underlying causes for recurrent pyoderma.

2.  Pyodermas will not resolve completely and will recur until the dog is adequately supplemented with thyroid hormone.

3.  Pruritus can be seen in some dogs taking thyroid supplements that contain dyes.

4.  Failure to respond to the cephalexin indicated a need for culture and sensitivity.

5.  To use rifampin successfully, keep the maximum dose at 10 mg/kg/day.

6.  Topical therapy is a must to resolve pyoderma. Current evidence supports the use of chlorhexidine as the most effective antiseptic.

Daisy, Not Your Usual Pyoderma

Daisy is a 2-year female spayed Boxer with a history of pruritus associated with atopic dermatitis, as well as multiple outbreaks of mild pyoderma which had responded well to cephalexin. She was presented to her veterinarian for a recent acute eruption of pustules, for which she was treated again with cephalexin at 30 mg/kg twice daily. After 5 days she was much worse and was referred to our dermatology service. Physical examination showed a lethargic dog with a generalized eruption of variably sized superficial pustules on a hyperemic base. New lesions were developed as we examined the dog. She had a low-grade fever and appeared depressed.

We considered the possibility that this dog might have pemphigus foliaceus (PF), due to the sudden wave of pustules that developed as we observed the dog, but we couldn't rule out an infection, particularly with a methicillin resistant strain of Staphylococcus. We made a cytology to determine if we could find the acantholytic cells we would associate with PF. We did not find acantholytic cells; rather, we observed numerous toxic neutrophils and rod bacteria. We therefore suspected an infection with Pseudomonas aeruginosa.

Skin scrapings were done to rule out the possibility of demodicosis, and they were found negative. Material was obtained for culture and sensitivity by opening up the pustules with a 25 gauge needle and touching the swab to the exudate. We dispensed marbofloxacin (Zeniquin) to be given at 5.5 mg/kg once daily and a chlorhexidine shampoo to be used every other day. Five days later, the culture revealed Pseudomonas aeruginosa sensitive to amikacin, gentamicin, marbofloxacin, and intermediately sensitive to enrofloxacin. When we reported this to the owner, she said that Daisy was showing significant improvement already and that she was no longer depressed. We continued the oral marbofloxacin and decreased the bathing to twice weekly, with a plan to see the dog in about 2 weeks.

Two weeks later, Daisy was much improved in her demeanor and the pyoderma was about 90% resolved. Because there were a few active lesions present, we decided to continue the marbofloxacin for an additional week. One week later, Daisy returned and the pyoderma was completely resolved. Intradermal skin testing was performed and Daisy was found to be allergic to multiple pollens, house dust mites, human dander, and Malassezia yeast. Injection immunotherapy was begun, and we recommended that weekly bathing be continued. Daisy did not relapse with pyoderma again, and she had a favorable response to immunotherapy, requiring very little medication to control her itch.

Important Points

 The most common cause of canine pyoderma is Staphylococcus pseudintermedius; however, infection with Pseudmonas aeruginosa is not rare. It often occurs as a result of a grooming incident, although not in this dog.

 The use of cytology allows the identification of a bacterial rod quickly; culture and sensitivity is recommended in these cases.

 Infection with gram-negative rods is an indication for the use of fluoroquinolones; these antibiotics are not recommended for the routine treatment of staphylococcal infections.

 Topical therapy should be a part of the management of all pyoderma.

General Summary

These two dogs represent more severe cases of pyoderma. In general practice, it is important to develop a protocol that will allow for the effective treatment of pyoderma, while minimizing the risk of resistance. The most important part of pyoderma management is the realization that canine pyodermas have an underlying cause that must be addressed. Staphylococcus pseudintermedius is an opportunist. There are many potential underlying causes of pyoderma, including parasitic diseases (demodicosis, scabies, fleas), endocrinopathies, and keratinization disorders, but in many parts of the world, allergies are the most common cause for recurrent pyoderma in dogs. Ideal management of pyoderma combines topical therapy with judicious use of antibiotics, considering safety, efficacy, and compliance. Guidelines for the treatment of superficial pyoderma have been published⁸; keep in mind that there will be geographic variation in the susceptibility patterns for S. pseudintermedius.

References

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8.  Hillier A, Lloyd DH, Weese JS, Blondeau JM, Boothe D, Breitschwerdt E, Guardabassi L, Papich MG, Rankin S, Turnidge JD, Sykes JE. Guidelines for the diagnosis and antimicrobial therapy of canine superficial bacterial folliculitis (Antimicrobial Guidelines Working Group of the International Society for Companion Animal Infectious Diseases). Vet Dermatol. England; 2014;25(3):163–1 75,e42–3.