Page 1528 - Clinical Small Animal Internal Medicine
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1466  Section 12  Skin and Ear Diseases

            as generalized muzzle,  periocular, and  pinnal involve-
  VetBooks.ir  ment clinically differentiate it from chin acne in many
            cases (see Chapter 164 for a more thorough discussion of
            juvenile cellulitis). Chin acne is supported by the pres-
            ence of cocci and a mixed population of inflammatory
            cells on cytologic evaluation.
              Treatment involves systemic antimicrobial therapy,
            ideally based on aerobic culture and sensitivity testing
            (see “Treatment of pyodermas” section below), with adjunct
            topical antimicrobial therapy. Benzoyl peroxide gel, silver
            sulfadiazine cream, clindamycin cream, and mupirocin
            (reserved for resistant staphylococcal infections), are
            often  well tolerated when applied to the facial area.
            Because furunculosis and subsequent deep pyoderma are
            frequently present, treatment for a minimum of six weeks   Figure 166.12  Dorsal interdigital nodule with hemopurulent
            may be required. Treatment should be continued for two   exudate due to furunculosis and deep staphylococcal pyoderma
                                                              in a cairn terrier.
            weeks past clinical and palpable resolution.

            Interdigital Pyoderma                             Treatment of this condition may include multiple carbon
            Interdigital pyoderma has a diversity of presentations and   dioxide (CO 2 ) laser ablations of the ventral cystic lesions
            therefore terms commonly used include canine pododer-  in addition to antimicrobial therapy as described subse-
            matitis, pedal folliculitis/furunculosis, and interdigital   quently in this chapter (see “Treatment of pyodermas”).
            “cysts.” Lesions may include interdigital erythema, sali-  Diagnosis involves obtaining a thorough history and
            vary staining of hairs, papules, nodules, hemorrhagic bul-  performing a physical examination to identify possible
            lae, and draining tracts. Clinical signs may include licking   primary causes. Deep skin scrapes or hair plucks for
            and biting of the feet, and lameness. Staphylococci are   demodicosis must be performed, as demodicosis may
            common bacterial etiologic agents of pododermatitis and   demonstrate all the aforementioned clinical manifesta-
            infection often occurs concurrently with Malassezia and   tions. In some cases of pododemodicosis, biopsy may be
            gram‐negative bacterial organisms. Interdigital pyo-  required for diagnosis.
            derma is a multifactorial disorder consisting of predis-  Perform multiple surface cytologic preparations of
            posing abnormal conformation, primary etiologies, and   erythematous interdigital spaces to confirm the presence
            secondary infections that perpetuate the dermatitis.  of bacterial organisms as well as Malassezia. Consider
              Abnormal weight bearing as a result of abnormal con-  aspiration of nodules and hemorrhagic bullae to assess
            formation, musculoskeletal disease, and/or obesity are   for secondary bacterial infection and other causes of
            predisposing factors for the development of interdigital   nodular dermatitis, including neoplasia. Consider the
            pyoderma. In such cases, rather than generalized inter-  possibility of a foreign body, particularly in the context of
            digital involvement, focal dorsal or ventral dermatitis is   a solitary nodular lesion with mixed inflammation.
            often recurrent in one or several interdigital spaces.   Culture and sensitivity of tissue biopsies or aspirates of
            Short‐coated dogs such as Labradors and English bull-  nodular lesions should ideally be performed with con-
            dogs appear to be predisposed.                    firmed or suspected  bacterial involvement, as  such
              Hypersensitivity, autoimmune, and inflammatory con-  lesions indicate deep pyoderma and require prolonged
            ditions are primary etiologies; secondary bacterial and   therapy. Avoid culture of draining tracts as they may not
            yeast surface overgrowth and/or bacterial folliculitis per-  be reflective of the relevant bacterial organisms within
            petuate the dermatitis. Occasionally, hypothyroidism   the tissue.
            and hypercortisolism may result in interdigital bacterial   Pedal pruritus (licking and biting of the feet) with gen-
            or yeast overgrowth.                              eralized dorsal or ventral interdigital involvement per-
              A conformation‐related disorder involving ventrally   sisting despite resolution of secondary infection is
            oriented cystic follicles, primarily on the forelimbs, has   suggestive of cutaneous adverse food reaction or atopic
            been described. These dilated follicles may be grossly vis-  dermatitis.
            ible as comedones and milia. The cystic follicles rupture   Topical antimicrobial therapy is ideal for secondary sur-
            in the dermis. The subsequent foreign body response   face bacterial and yeast overgrowth. Chlorhexidine, ben-
            clinically manifests as dorsal interdigital nodules, hemor-  zoyl peroxide, or ethyl lactate‐based shampoos may be
            rhagic bullae, and edema (Figure 166.12). Draining tracts   used as a soak, particularly for painful feet, every 24–48
            and deep secondary bacterial infection frequently ensue.   hours initially. Aluminum acetate solution (Domeboro)
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