Download Screening and Management Considerations for the Geriatric Dog

Screening and Management Considerations for the Geriatric Dog and Cat
Sheri J. Ross, BSc, DVM, PhD, Dipl. ACVIM (Internal Medicine)
Significant advances in health care and nutrition in veterinary medicine has extended the life
expectancy of dogs and cats. Although “old age” is not a disease, it is a time when many
diseases are more likely to occur; often concurrently. Early detection of disease conditions
allows prompt intervention and more successful outcomes once treatment has been initiated.
Routine monitoring of the geriatric patient is essential to identify any new or emerging conditions
in addition to monitoring trends and response to therapy.
Significant advances in health care and nutrition in veterinary medicine has extended the life
expectancy of dogs and cats. As with humans, companion animals are living longer. The most
recent survey from the AVMA reported that 39% of the owned pet population in the United
States were ≥7 years of age. Although “old age” is not a disease, it is a time when many
diseases are more likely to occur, often concurrently. Early disease detection of disease
conditions allows earlier intervention and more successful outcomes once treatment has been
initiated. Routine monitoring is also helpful to monitor therapy, follow trends and identify any
emerging conditions.
The concept of senior wellness exams should be thoroughly explained to clients to increase
compliance. Clients need to be educated about the definition of a senior pet and the benefits of
detecting disease conditions early. The veterinarian should recommend patient testing to
establish a database when pets reach their senior years according to an age conversion chart.
Patients receiving long-term medications should be tested without exception.
Defining “Old-Age”
Generally speaking, patients > 8 years of age are considered to be geriatric. However the
influence of breed, genetics, nutrition and environment must also be considered. There is a
large disparity between the average life expectancy of a small breed dog and that or a large
breed dog. It may be clinically more appropriate to consider cats and small dogs (less than 20
pounds) to be geriatric after nine years of age, medium size dogs (21-59 pounds) at eight years
of age, large size dogs (51-90 pounds) at seven years of age and the giant breed dogs (more
than 91 pounds) at six years of age. If the owner is able to relate the age of their pet to the
equivalent human age, they are more likely to understand and consent to a geriatric screening
profile. (see Table 1). It may also be helpful to differentiate between a senior pet and a geriatric
pet. Although arbitrary, this distinction emphasizes to the owner the increasing risk associated
with advancing age and the need for additional diagnostic testing.
Patient evaluation
The minimum senior database should include a detailed medical history, comprehensive
physical exam, complete blood cell count (CBC), biochemical profile with electrolytes, complete
urinalysis and determination of thyroid function. Blood pressure is an important and often
overlooked component of the physical exam. As many common diseases of geriatric pets are
associated with hypertension. Depending on the clinical condition of the patient and the results
of the aforementioned tests, further testing may be indicated. A more complete senior panel is
outlined in Table 2.
Senior pets are more likely to have a multitude of disease with the most common being;
neoplasia, chronic kidney disease, hyperthyroidism (cats), hypothyroidism (dogs), dental
disease, diabetes mellitus, and arthritis. In addition, some deterioration in cognitive function and
sensory perception is often observed.
Virtually every organ system is affected by aging and it is important to differentiate true
pathology from expected, age related changes. When abnormalities are detected on screening
tests, they must be interpreted in conjunction with the clinical condition of the patient. When
assessing the results of any biochemical evaluation, it is important to define the “normal” range
in order to understand and appreciate the significance of reference values assigned to all
laboratory tests. Laboratory references ranges are typically established by measuring
biochemical parameters on a group of patients that have been declared “normal”. If an
adequate number of samples are obtained, the results should follow a bell-curve or normal
distribution. The references range is defined as the range of values that falls within two standard
deviations above or below the mean value. Therefore, by design, approximately 2.5% of the
“normal” population will have laboratory values that fall outside the upper and lower limits of
normal. When the minimum database is performed on a given patient, approximately 40
biochemical parameters will be assessed. Statistically, it is highly likely that at least one
parameter will fall outside of the normal range. It is incumbent on the clinician to assess the
magnitude of the abnormality. Assessment of the variance of a value outside the normal range
will differ among individual laboratory parameters. For example, a creatinine value of 1.5 x the
upper limit of the reference range definitely warrants further investigation, while an ALT of 1.5x
the upper limit may not.
The purpose of the above discussion was to stress the importance considering all aspects of the
clinical evaluation when dealing with senior patients. The remainder of the lecture will be
focused on the significance of some of the more commonly detected biochemical abnormalities
and the diagnostic plan once they have been discovered. Although problems with the
cardiovascular and gastrointestinal system are fairly common in senior pets, disorders of these
systems are more readily identified on physical exam and clinical history. Changes in
biochemical parameters are not consistent or typical and will not be discussed here.
Selected biochemical abnormalities of senior pets
Elevated liver values
One of the more commonly reported biochemical abnormalities of senior pets are isolated
elevations in alanine transaminase (ALT) and/or alkaline phosphatase (ALP). Assessment of
tests of liver injury should be approached in a stepwise and cost-effective methodological
manner, particularly if they are discovered in an otherwise normal patient. Normal ALT and ALP
values vary depending upon other factors such as age, weight, time of day, and level of
exercise. Unfortunately many tests of liver injury are neither highly sensitive nor specific. Thus, it
is imperative that the clinician confirms the result of an abnormal test by either repeating it
and/or ordering a more specific one. Initial evaluation of all patients with persistent ALT /ALP
elevations should include a thorough and accurate history and physical examination. The history
must include questions about previous diseases, prescription and non-prescription medications
or supplements, diet, environment, etc.
In asymptomatic patients with mild elevations of transaminases (less than two times the upper
limit of normal) or those with a low pretest probability of having liver disease the clinician should
decide if and when to repeat the evaluation. With mild changes, further diagnostic testing is not
indicated until the abnormality has been documented as being persistent or progressive. The
interval at which to repeat the abnormal test in asymptomatic patients with mild disease has not
been firmly established.
A persistent mild elevation in ALT in a cat should prompt evaluation of thyroid function, while a
more significant elevation (>4x normal) combined with clinical signs and biochemical findings
(hypoalbuminemia, hypoglycemia, hyperbilirubinemia, etc.) of liver disease should prompt a
hepatobiliary investigation. This would include liver function testing (bile acids), hepatic
ultrasound and potentially hepatic biopsy. The evaluation should proceed in a step wise fashion,
and the risks and benefits of more invasive procedures such as biopsy should be evaluated.
Azotemia
Chronic kidney disease is an extremely common disease in senior pets, particularly cats. Many
cats are diagnosed with kidney disease on pre-anesthetic lab work. Any elevation of BUN and
creatinine, in a clinically hydrated animal, outside of the normal range (and even within the high
end of the normal range) warrants further investigation. When performing blood work on senior
pets, it is very important that a urinalysis be obtained concurrently to help differentiate pre renal
causes of azotemia from intrinsic renal disease. If the azotemia is mild and paired with an
inappropriate urine specific gravity (ie. isosthenuric), the patient should be evaluated to assess
the degree of kidney disease. Recommended evaluations included a complete urinalysis, urine
protein determination, urine culture, blood pressure, and imaging (ultrasound and/or
radiographs). Other clinical syndromes that are commonly associated with chronic kidney
disease
include
anemia,
hypertension,
metabolic
acidosis,
hypo/hyperkalemia,
hyperphosphatemia, hypoalbuminemia, and urinary tract infection. Once a diagnosis of kidney
disease has been established, treatment recommendations will depend on the extent and
severity of the associated abnormalities. Treatment guidelines specific to the stage of kidney
disease are provided by the International Renal Interest Society (IRIS) at www.iris-kidney.com.
There is an increased incidence of urinary tract infections in older pets most likely due to a
combination of a decrease in the effectiveness of the immune system and the frequency of
comorbid disease states that predispose to urinary tract infections. (eg, chronic kidney disease,
diabetes mellitus, Cushing’s, etc.). It is recommended that patients diagnosed with any of these
disorders have a quantitative bacterial urine culture performed. Clinically silent bacterial urinary
tract infections have been documented in up to 50% of dogs with diabetes or Cushing’s.
Endocrine disorders
Endocrine diseases appear with greater frequency in senior pets. The most commonly
encountered endocrine diseases include hypothyroidism (dogs); hyperthyroidism (cats);
diabetes mellitus; and hyperadrenocorticism. Thyroid function testing is recommended as part of
the minimum senior screening database for both dogs and cats. If a T4 has not been measured,
there are other clinical findings that should raise the index of suspicion for thyroid disease and
prompt further investigation. Dogs with hypothyroidism may have typical physical exam findings
including a poor haircoat, lethargy, and weight gain. A common biochemical abnormality is
elevated cholesterol. In contrast, cats with hyperthyroidism may be active, exhibit weight loss
despite a good appetite and may have a heart murmur. The most common biochemical
abnormality is a mild to moderate elevation in ALT. Dogs with persistent elevations in ALP and
consistent clinical signs (poor hair coat/hair loss, weight gain, panting, pot-belly, excessive thirst
and appetite, should be evaluated for Cushing’s disease. Screening tests such as a urine
cortisol to creatinine ratio is a good screening test, but should not be used as a confirmatory
test. If Cushing’s disease is suspected, it may be confirmed with a low dose dexamethasone
suppression test or ACTH stimulation test. Other diagnostic testing should include an abdominal
ultrasound, urine culture, and blood pressure determination.
Hypercalcemia
Hypercalcemia in dogs is most often associated with chronic kidney disease and
lymphosarcoma, although many other causes are certainly possible. Mild elevations in serum
calcium, in the absence of any other clinical findings should be monitored. Moderate to
significant increases in serum calcium should be evaluated rapidly to prevent the adverse
metabolic consequences; most notably, kidney damage. Parathyroid hormone and parathyroid
hormone-like assays that include the measurement of ionized calcium are helpful in the
differential diagnosis of hypercalcemia.
Hypergammaglobulinemia
Hypergammaglobulinemia is a relatively common biochemical abnormality, especially in cats.
Most often, mild hyperglobulinemia is associated with significant dental disease. Marked
hyperglobulinemia should prompt further investigation. Any chronic inflammatory or neoplastic
disease can result in elevated gammaglobulins via immune stimulation (eg inflammatory liver
disease). Serum protein electrophoresis is useful in determining if monoclonal or polyclonal
gammopathy is present. Radiographs will help to rule out multiple myeloma.
Anemia
Mild anemia is a common clinical finding in older pets. Anemia of chronic disease, chronic
kidney disease and many neoplasias are associated with a normocytic, normochromic, nonregenerative anemia. Regenerative anemia is usually the result of blood loss. Patients with nonregenerative anemia should be screened for intestinal parasites. Clinical history may provide an
indication of gastrointestinal blood loss (ie. melena). Immune mediated destruction of red blood
cells will also result in a regenerative anemia, but this is usually associated with cancer in older
pets. Hemangiosarcoma is an example of neo-plastic-induced blood loss anemia. Bone marrow
examination is especially important in determining the cause of nonregenerative anemias.
Thrombocytopenia
Potential etiologies of thrombocytopenia include immune-mediated destruction, disseminated
intravascular coagulation, platelet sequestration, and decreased bone marrow production.
Neoplastic diseases may result in thrombocytopenia via one or a combination of these disease
mechanisms. Measurement of platelet factor 3 assists in the diagnosis of immune-mediated
thrombocytopenia.
There are many other abnormalities, but time and space preclude their discussion here.
Treating the senior patient
Once a disease has been diagnosed, it is important to re member that age-related changes in
physiology may alter the pharmcokinetics of many drugs. Most drugs are metabolized via the
liver or kidney. Liver disease, hypoalbuminemia (albumin binds many drugs), CKD, and chronic
dehydration occur frequently in older patients and impact drug metabolism. When treating
geriatric patients, the dose and/or dosing intervals of some drugs may therefore need to be
altered.
While veterinary medicine can often offer sophisticated therapeutic options, it is important to
remember that older patients are often poorly tolerant of the stress involved with hospitalization
and repeat examinations. Each diagnostic and treatment plan must be tailored to the individual
patient.
Table 1: Estimation of the human equivalent age of dogs and cats. *
Pet Age Human Equivalent Age (years)
(years)
Feline
Canine
1-10 Kg
11-25 Kg 26-60Kg
3
28
28
29
31
4
32
33
34
38
5
36
38
39
45
6
40
42
44
52
7
44
46
49
59
8
48
50
54
66
9
52
54
59
73
10
56
58
64
80
11
60
62
69
87
12
64
66
74
94
13
68
70
79
14
72
74
84
15
76
78
89
16
80
82
94
17
84
86
18
88
90
19
92
94
20
96
* table used with permission from Dr. Wiliam D. Fortney
>60Kg
39
49
59
69
79
89
99
Adult
Senior
Geriatric
Table 2: Example of a comprehensive screening panel for senior patients.
Diagnostic test
Thorough medical history
Complete physical examination
Complete blood count
Blood pressure
Complete chemistry profile
Thyroid evaluation
Complete urinalysis
Urine culture
Urine protein:creatinine
Fecal examination (zinc sulfate flotation)
ECG/ Echocardiogram
Thoracic and abdominal radiographs
Urine cortisol:creatinine ratio
Medical, surgical, vaccination, dietary,
behavioral and travel history.
Including fundic exam
Include differential white blood cell count
Including electrolytes
Obtain sample by cystocentesis
If any proteinuria detected on UA
Especially if arrhythmia/murmur auscultated
Dogs: screening for Cushing’s disease.
If laboratory abnormalities are discovered on any patient, further testing may be warranted.
Remember that it is always important to consider any laboratory result in context with the history
and clinical status of the animal. The following are recommendations for follow-up testing in the
event that abnormalities are detected and verified on any of the screening laboratory tests. An
early diagnosis in many cases allows for a better chance to control a problem.
Table 3: Initial Follow-Up Recommendations for selected biochemical abnormalities
commonly found in senior pets. The first step with any abnormality is to verify the
problem.
Abnormality
Increased liver enzymes
Increased BUN/creatinine (Azotemia)
Anemia
Hyperglycemia
Hypoalbuminemia
Proteinuria
Glycosuria
Initial Work-up
- Repeat biochemical panel in 2-4 weeks to
reassess enzymes
- Bile acids (both pre and post prandial to
assess liver function
- Check T4 first in cats over 5 years of age
- Urine cortisol:creatinine ratio or another
screening test for Cushing’s in dogs
- Complete urinalysis
- Urine culture (cystocentesis)
- Urine protein:creatinine ratio
- Blood pressure
Repeat
panel
(complete,
including
phosphorus and electrolytes) in 2-4 weeks to
determine progression
- Reticulocyte count
- Evaluation of MCV, MCHC
- Fecal (parasites, occult blood)
- Iron stores
- Bone marrow evaluation
- Stress induced (cats)
- Repeat blood glucose (fasting)
- UA to detect glucosuria
- Fructosamine
- Urinalysis
- Urine protein:creatinine ratio if there is
proteinuria
on UA(assess magnitude of
proteinuria)
- Bile acids (pre and post prandial) to assess
liver function
- Assess for primary GI disease, especially if
panhypoproteinemic.
- Complete urinalysis
- Urine culture
- Urine protein:creatinine ratio, if culture
negative and benign sediment on UA
- Blood glucose