Study Case – A German Shepherd Dog with Hypercalcemia

Dave M. Klugman, DVM; Irina Kim, BS; Heather L. Tarpley, DVM; Kenneth S. Latimer, DVM, PhD; Perry J. Bain, DVM, PhD; Bruce E. LeRoy, DVM, PhD; Christopher R. Gregory, DVM, PhD

Class of 2005 (Klugman, Kim), Department of Pathology (Tarpley, Bain Latimer, LeRoy), and Department of Small Animal Medicine (Gregory), College of Veterinary Medicine, University of Georgia, Athens, GA 30602-7388

Signalment - Canine, German Shepherd Dog, M/N, 6-year-old

Presenting problems - Weight loss, vomiting, and lethargy

Medical history – Azotemia and hypercalcemia

Laboratory Data -

1. Thrombocytopenia with increased mean platelet volume. Platelet aggregates were not observed on the stained blood film indicating that thrombocytopenia was not the result of platelet aggregation or laboratory error. In this patient, platelets are probably being consumed or destroyed and replaced by more immature platelets that have an increased mean platelet volume.

2. Echinocytes. Echinocytes (also known as crenated erythrocytes) may appear as an artifact caused by glass effects, slow drying of the blood smear, or pH shifts when blood smears are prepared. Alternatively, echinocytosis also may be associated with ATP depletion or uremia. For additional information on echinocytosis, please see http://www.vet.uga.edu/vpp/clerk/Stello/index.php.

3. Reactive lymphocytes. Reactive lymphocytes are large cells with moderately condensed chromatin, a scalloped nuclear margin, and a thin rim of dark blue cytoplasm. The presence of these cells suggests nonspecific antigenic stimulation.

4. Hypercalcemia. Differential diagnoses for hypercalcemia include hypercalcemia of malignancy, primary hyperparathyroidism, hypervitaminosis D (toxic or iatrogenic), hypoadrenocorticism, and chronic renal failure. Careful palpation of the lymph nodes and rectal area is indicated in any patient with hypercalcemia because hypercalcemia of malignancy is most common. Lymphoma and apocrine gland carcinoma of the anal sac are the two most common neoplasms associated with increased production of parathormone-related protein (PTHrP) and subsequent development of hypercalcemia. In this patient, digital rectal examination revealed a firm, 5 cm mass on the right side of the rectum. A fine-needle aspirate of the mass was highly cellular and composed of cuboidal epithelial cells in clusters and sheets, the appearance of which was consistent with an apocrine gland carcinoma of anal sac origin (Fig. 1). The cytologic diagnosis was subsequently confirmed by biopsy (Fig. 2).

Figure 1. Fine-needle aspirate of a rectal mass in a dog. Clusters of cuboidal cells have uniformly round, hyperchromatic nuclei and a thin rim of basophilic cytoplasm. Dog, apocrine carcinoma of anal sac origin, Wright stain.	Figure 2. Surgical biopsy of the rectal mass. Cuboidal epithelial cells are densely packed and have small, uniform, hyperchromatic nuclei and scant basophilic cytoplasm. Two mitoses are present. Dog, apocrine carcinoma of anal sac origin, hematoxylin and eosin stain.

5. Azotemia. Hypercalcemia has multiple effects on kidney function. First, the collecting duct response to antidiuretic hormone (ADH) is diminished leading to polyuria and polydypsia, hyponatremia, and decreased urine specific gravity. These changes are presumed to be caused by decreased cAMP concentration in collecting duct epithelial cells secondary to elevated serum calcium concentrations. Glomerular filtration rate also is decreased due to calcium-induced vasoconstriction of the renal vasculature. Pre-renal azotemia secondary to vomiting, diarrhea, and polyuria also may occur in hypercalcemic patients. In animals with a Ca x P product > 70, mineralization of soft tissues is possible. In this patient, the Ca x P product was 70.2 on the day of admission, indicating that the patient is at marginal risk of developing nephrocalcinosis. However, renal mineralization was not observed on survey radiographs indicating that any calcium deposition is likely to be reversible. Finally, serum calcium concentrations >14.0 mg/dl promotes hypercalciuria which increases the probability of urolithiasis.

6. Hyponatremia and decreased urine specific gravity. Both of these clinical abnormalities are caused by decreased responsiveness of collecting duct epithelial cells to ADH, leading to decreased sodium and water absorption and decreased ability of the kidneys to concentrate the urine.

7. Possible isosthenuria. A urine specific gravity ranging from 1.008 to 1.012 indicates that the kidney is not concentrating the urine, which is inappropriate in an animal with azotemia. However, further tests are necessary to determine if renal disease is actually present.

8. Positive blood reaction on urine dipstick. The blood indicator pad on the urine dipstick will react to intact erythrocytes (hematuria), free hemoglobin (hemoglobinuria), and free myoglobin (myoglobinuria). The presence of increased erythrocytes in the urine sediment indicates that hematuria is present. Blood contamination sometimes occurs during the collection of urine specimens by cystocentesis.

1. Thrombocytopenia with increased mean platelet volume. Please see above discussion.

2. Echinocytes. Please see above discussion.

3. Neutrophilia with mild toxic change and eosinophilia. Neutrophilic leukocytosis is an expected inflammatory response following surgery. The absence of a left shift indicates that the maturation and storage compartment of the bone marrow has an adequate supply of segmented neutrophils to meet tissue demands for these cells. However, the presence of mild cytoplasmic basophilia and Döhle bodies suggest toxic change of neutrophils that is sometimes observed in severe inflammation and infection. Eosinophilia may be associated with parasitism or hypersensitivity reactions (but the precise cause of this abnormality was not pursued in this patient). The previous eosinophil count (3/26) may have been slightly suppressed due to stress.

4. Hypocalcemia. After surgery, the source of PTHrP is eliminated and serum calcium concentrations would be expected to decrease, which did occur in this patient. However, the parathyroid glands can atrophy due to increased negative feedback from the elevated calcium concentration in the blood. In this patient, serum calcium was measured at 8.8 mg/dl on 04/01 indicating an inability of the parathyroid gland to respond to low blood calcium by increasing the release of parathormone (PTH). Therefore, supplementation with calcium carbonate was required to normalize serum calcium concentration. Mild hypocalcemia should always be assessed in light of the albumin concentration (not determined in this case). Furthermore, determination of the ionized calcium value may be useful because this is the biologically active fraction of total serum calcium.

5. Mild hyperkalemia. Potassium is largely an intracellular cation and serum concentrations are relatively low. The mild hyperkalemia may be due to ion exchange in acidosis, decreased glomerular filtration rate, or cellular injury. In this patient, acidosis is probably responsible for the mild hyperkalemia because surgical manipulation (injury) of tissue was not extensive and fluid therapy maintained renal perfusion for adequate potassium excretion. In acidosis, excess hydrogen ions in the extracellular milieu move intracellularly and are exchanged for potassium ions that move extracellularly. Thus, electroneutrality is maintained while the acidosis is partially abrogated.

6. Metabolic acidosis and anion gap within the reference interval. Decreased bicarbonate without an increase in the anion gap indicates a secretory acidosis (increased loss of bicarbonate). Possible causes for secretion-type acidosis include diarrhea, intestinal fluid sequestration, increased salivation, and increased renal loss.

7. Azotemia. See discussion above.

Additional diagnostic tests – A fine-needle aspirate of the mass was consistent with apocrine carcinoma of anal sac origin (Fig. 1). This cytologic diagnosis subsequently was confirmed by surgical biopsy which indicated that the neoplasm was locally invasive and incompletely excised (Fig. 2).

Patient outcome - The mass was debulked at surgery. However, its location and local neoplastic cell infiltration prevented complete surgical excision. Post-operative treatment included fluid therapy to promote renal perfusion and administration of a vitamin D analog to prevent hypocalcemia.

In summary, apocrine carcinomas of anal sac origin commonly are associated with hypercalcemia (serum total calcium averaging 16.1 mg/dl). These neoplasms usually are unilateral. Apocrince carcinomas of anal sac origin are observed most commonly in older (7 to 16 years of age), female dogs. Excision of these neoplasms may result in normocalcemia, while tumor regrowth or metastasis may be associated with hypercalcemia. These malignant neoplasms usually spread via local tissue invasion and lymphatic channels. Metastasis may involve the sacral, iliac, and sublumbar lymph nodes as well as the lung, liver, and spleen.

References

1. Feldman EC, Nelson RW: Canine and Feline Endocrinology and Reproduction. St. Louis, W. B. Saunders Co., 2004, pp. 416-436.

2. Osborne CA, Finco DR.: Canine and Feline Nephrology and Urology, Baltimore, Williams & Wilkins, 1995, pp. 669-673.

3. Latimer KS, Mahaffey EA, Prasse KW: Duncan & Prasse’s Veterinary Laboratory Medicine: Clinical Pathology, 4th ed. Ames, Iowa State Press, 2003, pp. 65-69, 72-74, 270-278.

4. Moulton JE (ed): Tumors in Domestic Animals, 3rd ed. Berkeley, University of California Press, 1990, pp. 73-75.

Image of "German Shepherd" by Gill Evans is from the Webury Gallery website.

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