Download the polyuria polydipsia problem

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
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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
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The North American Veterinary Conference — 2006
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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.
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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
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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.
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