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PROCEEDINGS OF THE NORTH AMERICAN VETERINARY CONFERENCE VOLUME 20 JANUARY 7-11, 2006 ORLANDO, FLORIDA SMALL ANIMAL EDITION Reprinted in the IVIS website (http://www.ivis.org) with the permission of the NAVC. For more information on future NAVC events, visit the NAVC website at www.tnavc.org Exotics — Avian ______________________________________________________________________________________________ THE POLYURIA / POLYDIPSIA PROBLEM Susan E. Orosz, PhD, DVM, Diplomate ABVP (Avian) and ECAMS Perrysburg Animal Care Perrysburg, OH Birds have a kidney that is a cross between reptiles and mammals so their droppings reflect this difference. The normal droppings of birds consist of a partially coiled or soft mass of stool surrounded by a portion of white crystalline urates and often an outer portion of liquid urine. The stool originates in the intestinal tract but is stored in a part of the cloaca termed the coprodeum. It may acquire a coiled shape as observed in budgies and cockatiels from its storage in the cloaca. The kidneys of birds commonly are not bean-shaped organs that hang from the dorsal body wall as in mammals, but are firmly attached to the synsacrum and sit within the renal fossae. They extend from the lungs cranially to the distal end of the synsacrum caudally. Extensions of the abdominal air sacs from the pelvis can be found between the synsacrum and the kidneys. The combined mass of both kidneys are proportional to body mass. Birds without salt glands have 0.8% of their body mass as kidney tissue, while those with salt glands have 1.4%. The kidneys of bird do not have lobes as in mammals but have anatomical divisions. Each kidney has a cranial, middle, and caudal division. These divisions are often demarcated by the large arteries that run through this elongated organ. From a clinical perspective, it is important to note that the spinal nerves from the lumbar and sacral plexuses pass through the substance of the kidney. Nerve impairment to the pelvic limb from swelling or pressure as with neoplasia can result in neuropraxis or proprioceptive deficits to the limb. The avian kidney contains 2 basic types of nephrons—cortical or reptilian-type nephrons and the medullary or mammalian-type nephrons that contain medullary loops of Henle. The cortical type of nephron, as the name implies, is found in the cortical region only and does not have loops of Henle. They form the majority of the nephrons in the kidneys of birds. This is the type of nephron found in reptiles and these nephrons secrete primarily uric acid. The medullary type has a loop of Henle like in mammals that has a potential for producing and, to a certain extent, concentrating urine. However, avian kidneys are not as efficient as mammalian kidneys at concentrating urine. Medullary nephrons generally make up about 10% of the avian kidney. There appear to be habitat-related patterns to kidney structure as well–those species that live in an arid environment tend to have smaller kidneys, a larger medullary volume, and/or a smaller cortical volume. This is reflected in a dropping that is often devoid of urine where those that have more mammalian nephrons produce more urine. Birds are able to concentrate the urine produced in their mammalian nephrons often at 2–3 times that of plasma. The urinary concentrating ability generally varies inversely with body mass so that small birds (10–25 g) typically concentrate to 1000 mmol/kg, while birds greater than 500 g concentrate to 600–700 mmol/kg. Urine is normally stored in the urodeum of the cloaca. Further concentration of urine occurs by retroperistalsis of the urine up into the coprodeum and the large intestine. Both the coprodeum and the large intestine have a single layer of a columnar epithelium that has a great re-absorptive capacity for water. Urine production is controlled by arginine vasotocin (AVT). AVT is an 8-amino-acid peptide hormone that is released by the neurohypophysis. The most common reason for AVT release is a rise in extracellular fluid osmolality. Dehydration also results in an increase in circulating levels of AVT. As the AVT rises, the glomerular filtration rate is reduced, leading to reduced urine flow. Cortical nephrons are most sensitive to AVT. COMMON ABNORMAL DROPPINGS Abnormal urates or urine is often the result of polyuria. Polyuria presents in birds as a large volume of clear urine with little or no discoloration. Small amounts of crystalline urates may be present but the stool portion of the droppings is often well formed. If the urates are abnormal in color, that signals a problem that needs clinical attention. Yellow, lime green or bright green urates indicated that there is biliverdinuria or other bile pigment discoloration. This should point the clinician to look at liver causes, some of which may be infectious in origin like psittacosis. Pinkish or reddish urine or urates are the result of hematuria or hemoglobinuria. A port wine color to the urates of Amazons is associated with lead toxicosis. Other conditions that affect clotting or hemorrhage within the kidneys can cause this discoloration as well. A liquid stool (except in lories and other nectivores) is regarded as true diarrhea. This may be caused by a variety of factors ranging from decreased transit time, infectious bacterial, fungal, viral or parasitic enteritis to malabsorption. Dyes and other coloring agents from ingested foods are common causes of color changes that may stain the urine or urates as well. Beets, blueberries, blackberries, pomegranates and other fruits may cause color changes. Dyes in pelleted foods often result in the same type of discoloration. Colored newspaper may give the appearance of a change in the color of the droppings retroactively. Polydipsia often accompanies polyuria as it is a consequence of the fluid loss. However, some birds develop psychogenic polydipsia that results in polyuria. Water deprivation testing may be needed in these patients but should be performed with caution. DISEASES WITH POLYURIA/POLYDIPSIA There are a variety of diseases that can cause polyuria/polydipsia (PU/PD) in birds. The history should include information on the diet, its social and behavioral interactions and recent medications. In pigeons, it should include vaccination status as paramyxovirus serotype 1 can cause severe PU/PD. Hens that are about to lay 1563 The North American Veterinary Conference — 2006 ______________________________________________________________________________________________ eggs or those with possible peritonitis may have PU/PD as well. The behavioral history may point the bird to psychogenic polydipsia with secondary polyuria. Particularly in the smaller psittacines, PU/PD has been observed in those consuming a larger part of their diet as extruded kibble. Lesions were limited to nonspecific tubular nephrosis in those with suspected diet induced disease and where the kidneys were examined histopathologically (pre- and postmortem. The condition appeared to be reversible after feeding a non-pelletized diet for 1–3 months. Budgies and cockatiels in the wild are obligate seed eaters and so may require some seed in their diet. There are a number of diseases or conditions that are associated with PU/PD. A list of diseases include those of metabolic origin: liver disease, kidney disease, diabetes mellitus, and diabetes insipidus; those associated with diet: dietary-induced polyuria, excess fruit consumption, psychogenic polydipsia, excess dietary sodium, calcium or vitamin D and excess dietary protein; those secondary to medications: diuretics, gentamicin, corticosteroids, and progestins; renal glucosuria in African greys, paramyxovirus in pigeons, and excitement or fear when they come to visit the avian veterinary hospital. DIAGNOSTIC TESTING Diagnostic testing should be tailored to the history and clinical examination of the avian patient. Because uric acid is produced in the liver as a byproduct of protein metabolism and secreted in the reptilian nephrons, these organs need to be considered with PU/PD. Biochemical analysis of the plasma should include glucose, uric acid, AST, LDH, calcium, phosphorus, total protein, CPK and bile acids. A CBC and plasma electrophoresis may help determine if there is inflammation/ infection. Urinalysis Biochemical and cytological sediment analysis of avian urine is potentially useful in PU/PD. Wax paper should be placed in the cage floor and the bird allowed to void several droppings for analysis. The liquid urine should be aspirated with a 22g needle on a 1–3 ml syringe with minimal pressure as to not disrupt the cells or granular casts. The sample in the syringe should be held upright in a wire rack for 5 minutes so that the sediment can fall into the tip of the syringe before applying to the surface of a slide, cover slipped and the a drop of sedi-stain applied. The remaining sample can be checked for glucose and the simple dip stick tests can be performed. Hematuria may be noted on the urinalysis but its source needs to be determined. It may originate from the kidneys, reproductive tract or the GI tract. Toxic, neoplastic, bacterial and viral nephropathies may be associated with hematuria in birds. White blood cells have been observed in the urine sediment from approximately half of the pigeons with paratyphus, many of which had interstial nephritis. Sediment analysis should be a part of an avian urinalysis and specific cellular urinary components have been discussed. 1564 Several significant factors complicate interpreting avian urinalysis. First, urine is mixed with feces in the cloaca. The one possible exception is the ostrich, which appears to eliminate urinary waste separate from the feces. Second, in many species ureteral urine is refluxed into the large intestine where water, and sometimes electrolyte reabsorption takes place. Additionally, diseases of the lower intestine may alter urine production and composition. Gastrointestinal bleeding, inflammation, normal and abnormal organisms, etc may end up in an urinalysis. This could result in the false impression that red and white blood cells and/or infectious agents, respectively, came from the urinary tract. In short, the “urine” present in a dropping is not the same urine produced from the kidneys. Urinalysis results should be carefully interpreted because of the contamination of material from the GI tract. Water Deprivation Testing Water deprivation testing is considered when attempting to rule out unknown causes of polyuria/polydipsia (PU/PD) including central and nephrogenic diabetes insipidus and psychogenic polydipsia. Water deprivation results in increased plasma osmolality, which should then increase urine concentration. A presumptive diagnosis is based on whether birds can concentrate their urine. Birds with diabetes insipidus become dehydrated (as supported by plasma variables) but maintain dilute urine (low specific gravity and osmolality). There are numerous causes of PU/PD in birds that must first be ruled out using a complete history with a clinical examination followed by laboratory evaluation. A gradual water deprivation is preferable over sudden deprivation because it allows the kidneys and cloaca to respond gradually to the increasing plasma osmolality. Severe dehydration can result if the bird cannot concentrate urine and patients should be carefully monitored. Some of the many causes of PU/PD in birds include organic (liver, kidney, intestine, cardiac, etc), endocrine (diabetes mellitus) and metabolic (hyercalcemia) diseases. Radiography Plain and contrast radiography, nuclear scintigraphy, ultrasound, magnetic resonance imaging, and computed tomography (CT) can be used to inspect the avian kidneys. Imaging of the avian renal system is difficult because of the air sacs and its location within the ventral synsacrum. Indirect methods such as positive contrast radiography of the alimentary tract may be helpful in outlining renal masses. TREATMENT Treatment is based on the diagnosis of the cause for the PU/PD. If the cause is renal failure, then the bird may benefit from diuresis. Most commonly in birds, electrolyte solutions are provided by subcutaneous, intravenous or intraosseous routes. Lasix may also be administered but mannitol is given infrequently. Exotics — Avian ______________________________________________________________________________________________ Allopurinol should be considered with hyperuricemia. Allopurinol’s main action is to decrease uric acid production. Low dose non-steroidal anti-inflammatories may be used but with caution as their effect on the kidneys in birds is not understood. Dietary management is important but controversial in regards to protein levels. Current human and veterinary literature both supports and refutes protein restriction in patients with renal disease. The current recommendation is to provide adequate levels of protein. Vitamin A or beta-carotene should be provided at normal levels along with balanced omega 3/6 polyunsaturated fatty acids (PUFA). These omega fatty acids are important in reducing proinflammatory mediators. 1565