Wednesday, April 6, 2011

Vaccine-Associated Sarcoma

OVERVIEW
Cats—vaccination may induce development of sarcoma (primarily fibrosarcoma) at the injection site, primarily in the muscle, skin, and subcutaneous tissues; malignant fibrous histiocytoma, osteosarcoma, rhabdomyosarcoma, and chondrosarcoma also associated
FeLV and rabies vaccines—most common
Interval from vaccination to tumor development—may be as short as several months
Metastasis common
Fibrosarcoma—prevalence in cats unknown; estimated at 20/100,000 cats

Uveal Melanoma - Cats

OVERVIEW
The most common primary intraocular tumor in cats
Usually arise from the anterior iridal surface with extension to the ciliary body and choroid
Tend to be flat and diffuse, not nodular (unlike intraocular melanomas in dogs)
Initially has a benign clinical and histologic appearance
Unique feature—may develop metastatic disease up to several years later
Metastasize to regional lymph nodes, numerous visceral organs (especially those in the abdominal cavity), lungs, and less commonly, the skeleton

Uterine Tumors

OVERVIEW
Rare tumors, arising from the uterine smooth muscle and epithelial tissues
Compose 0.3%–0.4% of tumors in dogs and 0.2%–1.5% in cats
Dogs—usually benign; leiomyomas, 85%–90%; leiomyosarcoma, 10%; other types (e.g., carcinoma, fibroma, fibrosarcoma, lipoma) rare
Cats—usually malignant (adenocarcinoma); include leiomyoma, leiomyosarcoma, fibrosarcoma, fibroma, and lipoma
Metastasis—may occur with malignant forms

Urolithiasis, Calcium Oxalate

DEFINITION
Formation of calcium oxalate uroliths within the urinary tract and associated clinical conditions

PATHOPHYSIOLOGY
Presence of hypercalciuria, hyperoxaluria, hypocitraturia, and defective crystal growth inhibitors

Hypercalciuria
In dogs, normocalcemic hypercalciuria is thought to result from either intestinal hyperabsorption of calcium (so-called absorptive hypercalciuria) or reduced renal tubular reabsorption of calcium (so-called renal-leak hypercalciuria). Hypercalcemic hypercalciuria results from excessive glomerular filtration of mobilized calcium, which overwhelms normal renal tubular reabsorptive mechanisms (called resorptive hypercalciuria, since excessive bone resorption is associated with high serum calcium concentrations).

Hyperoxaluria
In humans, hyperoxaluria is associated with inherited abnormalities of excessive oxalate synthesis (i.e., primary hyperoxaluria), excess consumption of foods containing high quantities of oxalate or oxalate precursors, pyridoxine deficiency, and disorders associated with fat malabsorption.

Hypocitraturia
Urine citrate inhibits calcium oxalate urolith formation. By complexing with calcium ions to form the relatively soluble salt calcium citrate, citrate reduces the quantity of calcium available to bind with oxalate. In normal dogs, acidosis is associated with low urinary citrate excretion, whereas alkalosis promotes urinary citrate excretion.
Defective Crystal Growth Inhibitors
In addition to urinary concentration of calculogenic minerals, large-molecular-weight proteins in urine, such as nephrocalcin have a profound ability to enhance solubility of calcium oxalate. Preliminary studies of urine obtained from dogs with calcium oxalate uroliths revealed that nephrocalcin had fewer carboxyglutamic acid residues than nephrocalcin isolated from normal dog urine.