Featured case study:
5-year-old spayed female
Labrador retriever, Luna
Submitted by
Nina Morris, DVM, Cumberland Animal Clinic, Cumberland, ME
Complete history
Luna had a positive Lyme antibody result on
a SNAP® 4Dx® Test two years ago but
had no clinical signs of Lyme disease. As a precaution, her veterinarian treated her with
doxycycline (300 mg bid for two weeks). She has since been judiciously monitored for clinical signs
of Lyme disease and a Lyme Quantitative C6 Antibody Test performed three months later
was <10 U/mL. A concurrent SNAP 4Dx Test was negative. Luna is current on all appropriate
vaccinations and is on flea, tick, heartworm and intestinal parasite prophylaxis.
Physical examination
Luna was bright and alert and in good
body condition on presentation. Her weight has been stable and is currently 68.5 pounds. There were
no detectable abnormalities on the general physical examination. Rectal and vaginal examinations
were both unremarkable.
Differential diagnoses
Diabetes mellitus, diabetes
insipidus (central or nephrogenic), chronic renal failure, glomerulonephritis (previous history of
Lyme positive on SNAP 4Dx), hyperadrenocorticism, psychogenic polydipsia with medullary washout,
pyelonephritis, transitional cell carcinoma, vaginal or urethral mass and urinary tract infection
were all considered. Neurogenic (upper motor vs. lower motor neuron) and non-neurogenic
incontinence (hormone-responsive incontinence, urge incontinence) were also considered. Anatomic
abnormalities, such as ectopic ureter, patent urachus and vaginal stricture, were considered
unlikely given the patient’s age and the owner’s history of excellent compliance in reporting
unusual clinical signs.
Diagnostic plan
A complete blood count (CBC), general
chemistry profile, including electrolytes, complete urinalysis, and urine culture and sensitivity
were performed to screen for metabolic, inflammatory and infectious disease and to potentially
characterize primary and secondary organ involvement. If warranted, a urine protein:creatinine
(UPC) ratio would be included in the plan to help characterize any possible proteinuria that could
support early renal failure or Lyme-induced nephropathy.
Laboratory data
Erythron—There is a minimal and insignificant increased
hemoglobin concentration (HGB), which may represent a normal value for this animal or the
possibility of slight in vivo or in vitro hemolysis since the mean cell hemoglobin concentration
(MCHC) is on the high end of the reference interval. All other parameters are within reference
interval limits. No morphologic abnormalities are seen upon review of the blood film.
Leukon—All parameters are within reference interval limits. No
morphologic abnormalities are noted on blood film review.
Thrombon—No significant quantitative or morphologic abnormalities are noted.
Clinical chemistry
Kidney panel—There was a mild increase in both BUN and
creatinine suggesting a slight decreased glomerular filtration. Primary renal disease must be
strongly considered in the face of a nonconcentrated specific gravity. The finding of a slightly
increased sodium and a high within-reference-interval chloride was supportive of slight subclinical
dehydration and a prerenal component to the decreased glomerular filtration should be considered.
Further evaluation including characterizing any potential polyuria or polydipsia as well as
directly measuring water intake is warranted. In the urinalysis, there was a slight bacteriuria;
however, there was no sediment support for an active inflammatory process and the urine culture
was negative. These findings are occasionally seen and may be associated with contamination during
collection (free-catch specimen); repeat urinalysis would be warranted for further characterization. In the face of the mild decreased glomerular filtration rate and the nonconcentrated urine, repeat evaluation of the kidney chemistry profile, urinalysis and UPC ratio should be considered.
A repeat urinalysis on a free-catch specimen three days later revealed a 1.015 specific gravity, a
trace amount of protein and no red blood cells, white blood cells or bacteria seen. A UPC ratio was
also performed at this time and was within reference interval limits suggesting no significant
proteinuria. Also at this time, the BUN was within reference interval limits and creatinine was
just 0.1 mg/dL over the within-reference- interval limit; the creatinine value is well within the
third standard deviation from the mean for this parameter and the significance of this abnormality
must be questioned. Seven days later, the BUN and creatinine were the same and the creatinine was
interpreted to likely be “normal” for this animal; no previous data were available for comparative
purposes.
Diagnostic summary
Other than an initial mild decreased
glomerular filtration rate (corrected within three days without therapeutic intervention) and a
nonconcentrated urine specific gravity, all laboratory parameters returned to within reference
intervals. Furthermore, several weeks later, all laboratory parameters, including the BUN and
creatinine, were within reference intervals. Recently, the owner quantified water consumption for
one week with the average 24-hour intake being 4–5 cups. This would be considered normal water
consumption for a dog of Luna’s weight and well below 100 mL/kg/day, which would indicate
polydipsia. A clinical diagnosis of hormone-responsive urinary incontinence was made.
Therapeutic plan
The owner was offered a choice of
medications including phenylpropanolamine (PPA) and diethylstilbestrol (DES), and chose DES due to
the convenience of dosing. DES #30, 1 mg capsules, was dispensed with the following directions: one
capsule once daily for three days then one capsule weekly.
Clinical case outcome
Luna has responded well to DES
therapy with no obvious side effects and has had no further urinary accidents. The owner has not
observed any obvious PU/PD but will submit the urine for regular monitoring for proteinuria and
concentrating potential. A CBC will also be performed in one month to monitor for possible side
effects of DES therapy, such as pancytopenia. Side effects from DES therapy at low dosages are rare.
The UPC ratio testing
should always be performed on a urinalysis with an inactive sediment to prevent false-positive
results from protein originating from active inflammation or hematuria.
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