Paraneoplastic Syndromes in Small Animal Medicine

Paraneoplastic syndromes are abnormalities mediated through a tumor product that affects a distant organ or tissue. Paraneoplastic syndromes are important because some (hypercalcemia, hypoglycemia) can be life-threatening and require treatment prior to identification of the underlying disease; failure to consider tumors could lead to therapy that delays diagnosis. Suspicion of a tumor may be aroused only by the paraneoplastic syndrome in the absence of other clinical signs. Some infectious diseases mimic paraneoplastic syndromes, so recognition is critical for accurate diagnosis and prognosis. Response to therapy, or tumor recurrence, may be reflected in resolution, or reappearance, of paraneoplastic syndromes.

(Table 1. Paraneoplastic syndromes observed in the CBC)

Paraneoplastic syndromes recognized on laboratory results

Some common laboratory abnormalities, their proposed mechanisms, and associated tumors are in Tables 1 and 2; there are many other causes for the abnormalities listed.

(Table 2. Paraneoplastic syndromes observed in the biochemical profile or urinalysis)

Erythrocytosis can cause hyperviscosity syndrome, signs of which are attributed to poor tissue perfusion/ oxygenation from increased blood viscosity and include retinal hemorrhage, neurologic abnormalities (stupor, seizures), polyuria/polydipsia, weakness and lethargy. Thrombocytosis, often clinically silent, may increase the risk for thromboembolism as has been described in a cat with metastatic bronchogenic carcinoma. Clinical signs of thromboembolism are variable and reflect the organ/ tissue affected. Profound thrombocytosis (> 700,000/µl) can cause an artifactual serum hyperkalemia.

A hypoglycemic animal should have neither increased nor normal insulin concentration; the presence of either with hypoglycemia is suggestive of an insulinsecreting tumor. Abdominal ultrasonography can help rule out other intra-abdominal tumors that can cause hypoglycemia, and evaluate the liver, a common site of insulinoma metastasis

Hypercalcemia is often considered of malignant origin until proven otherwise. Hypercalcemia mediated by parathyroid hormone (PTH) or parathyroid hormonerelated protein (PTHrp) is usually accompanied by low, or low normal, serum phosphorous in a non-azotemic patient. After a thorough physical examination and review of routine laboratory results, assessment of PTH and PTHrp can be useful if hypercalcemia is seen with hypophosphatemia. Normal or increased PTH with hypercalcemia would suggest primary hyperparathyroidism; low PTH would suggest humoral hypercalcemia of malignancy. A normal PTHrp does not exclude a neoplastic cause of hypercalcemia. Increased PTHrp should prompt an aggressive tumor search paying particular attention to the anal sac region, thoracic and abdominal cavities. Lymphadenomegaly may be detectable only on thoracic radiographs or abdominal ultrasonography, so imaging may be done with, or instead of, measurement of PTH and PTHrp. Giving glucocorticoids to hypercalcemic patients can delay the diagnosis of lymphosarcoma if this disease is not readily apparent. Some infections that cause granulomatous inflammation can also cause hypercalcemia, lymphadenomegaly, and pulmonary nodules. [...]