Diagnosing and treating superficial pyoderma (Proceedings)

Superficial and deep pyodermas are undoubtedly among the most common problems a veterinary practitioner faces. It is important to recognize the clinical signs of pyoderma and perform appropriate diagnostics to identify this problem. Appropriate therapy should be instituted and then the case should be followed up in a timely manner to determine response to treatment and potential underlying issues. It is very unusual to diagnose a primary superficial or deep pyoderma in our pet populations. These issues are almost always secondary to another underlying process.

There are 3 levels of pyoderma discussed in most dermatologic texts and articles. These would include surface, superficial and deep pyodermas. In this lecture we will be concentrating primarily on the superficial and deep forms. In the superficial form, a pyoderma manifests primarily as folliculitis (e.g. papules, pustules, serous crusting, epidermal collarettes and "moth-eaten" alopecia). In the deep form, it is manifested to varying degrees by furunculosis, fistulae and hemorrhagic nodules. When diagnosing folliculitis, three very basic diagnostics should be considered. These include skin scrapings/plucks, dermatophyte culture and cytology (impression smears or Tzanck preparations). When investigating this type of lesion, these 3 basic diagnostics will help rule in/out the basic causes of folliculitis. Skin scrapings/plucks can help determine whether or not there are ectoparasites (e.g. Demodex canis) or dermatophytosis. Dermatophyte cultures obviously will rule in/out dermatophytosis. Cytology provides a plethora of information including types of white blood cells, presence of intra/extracellular cocci, rods, Demodex canis, acantholytic cells or fungal agents. Just based on these 3 tests, you are well on your way to determining the appropriate therapies. Often a CBC/chemistry screen urinalysis is indicated to more thoroughly assess for underlying conditions especially in cases of recurrent or deep pyodermas.

If this is a first time occurrence of the pyoderma, you can empirically select an appropriate antibiotic. Appropriate first line antibiotics could include cephalosporins, amoxicillin with clavulanate potassium, sulfur based antibiotics, erythromycin, lincocin or clindamycin. It is very important to be sure to use these antibiotics for at least 3 weeks in the case of a superficial pyoderma or 1 week beyond clinical resolution. It is important to also begin looking at underlying issues that may be contributing to this process. If this is a recurrent, non-responsive pyoderma or a deep pyoderma, then a culture of appropriate lesions should be performed and submitted to an appropriate laboratory. In cases of deep pyoderma, you will need to treat for at least 4-6 weeks or for 2 weeks beyond clinical resolution of the pyoderma. It is imperative in cases of recurrent or deep pyoderma to evaluate for an underlying process.

When evaluating for underlying processes, many factors must be considered including age of onset of the pyoderma, whether or not pruritus is present when the pyoderma is resolved and whether or not the lesions respond completely to antibiotics.

In cases with a young age of onset, the most common issues may include nutritional deficiencies, ectoparasites, immature immune system. Many of the dogs in the 6 month to 4 year old age group may have underlying allergies. In the middle-aged to older dogs, endocrinopathies or other metabolic disorders or food allergies may be an issue. In cases that have continuing pruritus despite resolution of the infection, underlying demodicosis or allergies should be considered. In cases where pruritus resolves upon treatment of the pyoderma, food allergies, immune suppression or endocrinopathies should be considered. These are, of course, general guidelines.

Bacterial cultures are very important in cases of antibiotic resistant pyodermas, recurrent pyodermas or if rods are seen on the cytology. It is becoming increasingly important to do a bacterial culture and sensitivity if cocci are noted on cytology and an infection is not responding to seemingly appropriate lengths and dosages of antibiotics as we are seeing increasing numbers of resistant Staphylococcus organisms. It is critical that the microbiology laboratories perform the tests to differentiate the different types of Staphylococcus and reliably test and report methicillin resistance. Since methicillin is no longer commercially available in the U.S., the laboratories will instead report resistance to oxacillin which is the basis for determining methicillin resistance in the U.S. If an organism is oxacillin resistant, beta-lactam antibiotics should not be used. These isolates also have variable resistance to rifampin, fluoroquinolones, macrolide antibiotics and tetracycline.

Methicillin resistant Staphylococcus aureus has been an increasingly common occurrence in human healthcare. Unfortunately, veterinary medicine is seeing a rise in cases of methicillin resistant Staphylococcus species as well. In a relatively recent study at University of Pennsylvania, they found the rates of methicillin resistance to be: S. aureus 35%, S intermedius (pseudintermedius) 17% and S. schleiferi 40%. Methicillin resistant Staph. schleiferi was more common in superficial infections whereas MRSA was more common in deep infections. It is very important when these cases are diagnosed to identify the correct antibiotics, get these cases on appropriate length of antibiotics and recheck prior to stopping antibiotics to be sure that the infection is completely resolved.

In addition to appropriate antibiotic therapy, appropriate topical therapies are considered very useful adjunctive therapy. This author believes that topical therapies may be gaining relevance as we are seeing more and more resistant Staphylococcal infections. However, topicals should be considered important in all bacterial infections of the skin. Many choices currently exist including chlorhexidine based shampoos, ethyl lactate based shampoo and benzoyl peroxide based shampoos.

It is essential when crafting a therapeutic approach for pyoderma to be sure to treat the infection until beyond clinical resolution, use appropriate dosages of the designated antibiotic and search for an underlying cause. In cases of recurrent/resistant pyoderma, it is quite important to be doing cultures to identify appropriate antibiotics. Topical therapy is nearly always an appropriate adjunctive therapy.