Our differential diagnoses for the dermatologic lesions included systemic lupus erythematosus (SLE), pemphigus complex, demodicosis
with furunculosis and secondary bacterial pyoderma, folliculitis or furunculosis secondary to a staphylococcal dermatitis,
dermatophytosis, erythema multiforme, toxic epidermal necrolysis, and canine juvenile cellulitis. We considered a drug eruption
less likely because there was no known history of drug therapy before the lesions appeared. Our differential diagnoses for
the acute-onset right tarsal joint effusion included an infectious arthritis, an immune-mediated arthritis (erosive or nonerosive),
and degenerative joint disease secondary to unknown trauma. Our differential diagnoses for the multiple subcutaneous nodular
lesions included infection (e.g. bacterial, fungal, parasitic, protozoal), sterile inflammatory disorders (e.g. nodular panniculitis, sterile granuloma or pyogranuloma syndrome, reactive systemic histiocytosis, xanthomas, canine juvenile
cellulitis), and, less likely, neoplasia. We attributed the dog's tachypnea to pain and the fever, and we attributed the nasal
planum depigmentation to irritation from the serosanguineous discharge from the skin lesions.
Initial diagnostic tests
The dog was hospitalized, and we performed a complete blood count (CBC), serum chemistry profile, and urinalysis. The abnormal
results of the CBC (Table 1) revealed leukocytosis with a regenerative left shift, 1+ toxic change, and monocytosis. These changes were consistent with
chronic active inflammation. We interpreted a nonregenerative, macrocytic, hyperchromic anemia as an anemia of chronic disease
with artifactual increases in mean corpuscular hemoglobin and mean corpuscular hemoglobin concentration from in vitro hemolysis.
The abnormal results of the serum chemistry profile (Table 1) revealed mild hyperphosphatemia, hyperglycemia, hypercholesterolemia, and a mild increase in alkaline phosphatase activity.
We attributed the elevated phosphorus concentration and alkaline phosphatase activity to physiologic increases associated
with growth. We attributed the hyperglycemia to stress and the moderate hypercholesterolemia to a postprandial increase.
Abnormal Laboratory Test Results
The results of urinalysis (sample collected by cystocentesis) revealed a slightly low urine specific gravity (1.020), hematuria
(80 to 100 RBC/hpf) and trace proteinuria. The hematuria was iatrogenic, and the results of a urine protein:creatinine ratio
to quantify the proteinuria and rule out concurrent glomerulonephritis were normal (0.43, reference range < 1). Serum was
also submitted for an antinuclear antibody titer.
Treatment and further tests
On Day 1, we initiated intravenous fluids (Plasmalyte 148 [Baxter] with 16 mEq/L potassium chloride added), morphine sulfate
(0.2 mg/kg subcutaneously q.i.d.), and cephalexin (22 mg/kg orally b.i.d.) as prophylaxis for secondary bacterial skin infections.
On Day 2, the dog remained febrile, and inguinal lymph node enlargement and additional truncal subcutaneous masses had developed.
The dog was anesthetized and prepared for arthrocentesis of multiple joints, including the right tarsal joint. We performed
arthrocentesis of the right stifle, right carpus, and both tarsi. The synovial fluid was grossly normal from all joints except
the right tarsus. The synovial fluid from the right tarsus was serosanguineous and had decreased viscosity. This joint had
been aspirated by the referring veterinarian five days before, so we suspected secondary iatrogenic blood contamination.
4. A photomicrograph of the dog's skin showing multifocal to coalescing pyogranulomatous inflammation surrounding several
follicles (hematoxylin-eosin; bar = 500 µm).
While the dog was anesthetized, we obtained multiple representative full-thickness 4-mm punch biopsy samples of abnormal tissue
from the periocular region, muzzle, chin, inner pinnae, prepuce, and truncal skin for histologic examination. The enlarged
lymph nodes and truncal subcutaneous masses were also aspirated for cytologic evaluation. Grossly, the aspirate of the right
submandibular lymph node appeared abnormal, consisting of serosanguineous fluid. The referring veterinarian had previously
aspirated this lymph node and noted an increase in plasma cells and lymphoblasts.