Successful Treatment of Disseminated Nocardiosis Caused by Nocardia veterana in a Dog

Yaemsiri, S.; Sykes, J.E.

A CBC revealed a mild normocytic (MCV 72 fL, RR 65-75 fL), normochromic (34.4 g/dL, RR 33-36 g/dL), nonregenerative anemia (HCT 37.5%, RR 40-55%), neutrophilic leukocytosis with left shift and slight toxicity (neutrophils 48,059 cells/lL, RR 3,000-10,500 cells/lL; band neutrophils 1,056 cells/lL), and a monocytosis Thoracic radiographs showed a diffuse bronchointerstitial lung pattern. On abdominal ultrasound examination, there was a focal, eccentric, nonobstructing mural mass within the jejunum that was associated with loss of intestinal wall layering. The mass was surrounded by mildly hyperechoic mesentery. The liver was mildly enlarged and hyperechoic. Echogenic debris was present within the gall bladder, but there was no evidence of biliary obstruction. Radiographs of the right carpus revealed marked soft tissue swelling of the antebrachium, carpus, and forefoot without osseous lesions. Aspirates and punch biopsies of the skin nodules revealed marked pyogranulomatous inflammation that included neutrophils that were mildly to moderately degenerated and activated macrophages with both intracellular and extracellular filamentous branching bacteria that morphologically resembled Actinomyces spp. or Nocardia spp. The skin biopsies were submitted for culture for aerobic and anaerobic bacteria, fungi, and mycobacteria. Smears of the biopsies revealed grampositive filamentous bacteria. Specimens were inoculated onto sheep blood agar plates, MacConkey agar plates, and tryptic soy broth and incubated at 35°C in 5% CO 2 until bacterial colonies were observed (48 hours). Treatment with cyclosporine was discontinued, the dose of prednisone was decreased (0.6 mg/kg PO q24h for 5 days), and treatment with ampicillin-sulbactam e (50 mg/kg IV q8h) was initiated. Subsequently, the results of special staining of the biopsy smears and biopsies became available. The biopsy smears contained filamentous organisms that stained positive with gram stain and Kinyoun stain, and negative with Ziehl-Neelsen stain. On histopathology, the intralesional bacteria stained positive with Kinyoun stain, weakly positive with Gomori's methenamine silver, but negative with Ziehl-Neelsen and periodic acid Schiff (PAS). The Brown and Brenn gram stain revealed abundant grampositive, filamentous, and beaded organisms. The history of immunosuppression, together with the positive Kinyoun stain, supported a diagnosis of disseminated nocardiosis rather than actinomycosis, so ampicillin-sulbactam was discontinued and trimethoprim-sulfamethoxazole (TMS) (30 mg/kg IV q8h) was commenced. A Schirmer tear test performed before initiating treatment with TMS revealed mildly decrease tear production (14 mm OD, 10 mm OS).