Page 309 - Withrow and MacEwen's Small Animal Clinical Oncology, 6th Edition

288 PART III Therapeutic Modalities for the Cancer Patient

channels). 34–36 The resulting inflammatory response and neuro- allow for a broader and more comprehensive view of the patient’s
nal injury lead to the increased nocifensive behaviors observed in general state and disease progression when establishing an analge-
sic regimen. Additionally, the examination of every patient must
patients undergoing chemotherapy. In these patients, pain usually
VetBooks.ir has an insidious development, but acute or subacute onset can be include palpation of the tumor area. One of the most useful ways
of determining if a tumor is painful is to palpate the area and
observed. Clinically, reported signs include paresthesia, abdomi-
nal pain, painful muscle cramps, burning-like sensations, numb- evaluate the animal’s response. This may not correlate precisely
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ness, and a specific paclitaxel-associated acute pain syndrome. with the amount of pain the animal spontaneously experiences,
Cisplatin, oxaliplatin, gemcitabine, vincristine, and others drugs but if a tumor is painful on manipulation or palpation, it is highly
can induce both peripheral and central modifications. To date, likely that spontaneous pain is associated with it. As veterinarians
only two reports have confirmed CIPN in veterinary medi- we struggle to measure spontaneous pain. It is perhaps reassuring
cine. 38,39 This low rate of reporting may reflect a truly low inci- that the way to measure spontaneous pain in rodent models is the
dence of CIPN in dog and cats or, alternatively, it may reflect the subject of considerable debate among researchers.
inability to diagnose accurately what may be a higher incidence of
low-grade subclinical CIPN. Currently no systematic studies in Clinical Metrology Instruments
veterinary medicine have annotated the prevalence of cancer pain
caused by chemotherapy. Given the difficulty in assessing pain, In humans the importance of patient-reported outcomes (PROs)
especially chronic conditions resulting from prolonged courses of is widely recognized. PROs may refer to a large variety of differ-
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chemotherapy, only subjective states of chemotherapy-induced ent health data reported by patients, such as symptoms, functional
pain have been evaluated, from the pet owner’s perspectives. 40–42 status, quality of life (QOL), and health-related quality of life
(HRQOL). QOL is a complex, abstract, multidimensional con-
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Assessment of Cancer Pain cept that defines an individual’s satisfaction with life in domains he
or she considers important. The designation HRQOL reflects an
The prevalence of cancer-related pain in humans ranges from 33% attempt to restrict this complex concept to aspects of life that are
in patients after curative treatment to 64% in the setting of meta- specifically related to the individual’s health and that potentially
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static disease. Despite the fact that pharmacologic strategies have could be modified by health care. In veterinary medicine assess-
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improved in the past 10 years, a significant fraction of surviving ing the effect of cancer in a companion animal’s life has become
cancer patients still endure pain that is ineffectively managed ; a fundamental practice to ensure an animal’s welfare. Assessment
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this makes chronic pain one of the key elements underlying dete- of the QOL has become a worldwide outcome measure in cancer
rioration in the quality of life of these patients. In small animal patients, and it is an extremely useful tool when making decisions
practices cancer is one of the leading causes of morbidity and about treatment and continuity of life.
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mortality. Even though currently no documentation exists of A pragmatic approach to the recognition of cancer-related pain
the actual prevalence of cancer pain in dogs and cats, it is reason- has been adopted in veterinary oncology and pain research, and the
able to deduce that a significant population of companion animals establishment of CMIs in clinical and research practice is essential
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experiences cancer-related pain during their disease progression, to reduce the inherent variability in pain assessment in animals.
in a manner similar to humans. CMIs use a proxy to provide information about the effect of both
Assessment of pain in animals, although often difficult, is disease and interventions in pets. The use of validated question-
extremely important. It is likely that the tolerance of pain by an naires has made pet owners an important component in the assess-
individual animal varies greatly and is further complicated by the ment of animals with painful diseases. Table 16.2 presents a list of
innate ability of dogs and cats to mask significant disease and pain. pain behaviors associated with cancer and/or cancer therapy in cats
It is important to remember that cancer pain significantly differs and dogs. Owners have the advantage of being able to detect behav-
from other types of chronic painful conditions, and differences ioral changes in their pets in nonstressful circumstances. However,
in clinical and behavioral manifestations among individuals and to evaluate properly behaviors affected by pain, in addition to the
breeds can be influenced by the type of cancer, tumor location, animal’s QOL, pet owners need to be educated by veterinary practi-
disease progression, and general state of the patient. In general, if tioners on what signs and behaviors may indicate pain.
a tumor is considered to be painful in humans, it is appropriate to Owner-completed questionnaires have been designed to mea-
give an animal with a similar condition the benefit of the doubt sure the severity of pain in dogs and cats. Several features are eval-
and treat it for pain. uated to determine pain severity and subsequent analgesic efficacy.
The approach of the author (BDXL) to the assessment of can- The best developed and validated of these were created to mea-
cer pain is to evaluate these aspects (Fig. 16.1): sure chronic musculoskeletal pain; in dogs they are the Liverpool
• Physical examination findings Osteoarthritis in Dogs 49,50 ; the Canine Brief Pain Inventory 51,52 ;
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• Owner observations using clinical metrology instruments and the Helsinki Chronic Pain Index ; and in cats it is the Feline
(CMIs) Musculoskeletal Pain Index. 54–57 Some work has focused on
• Activity developing cancer-specific owner questionnaires in dogs and cats
• Quantitative sensory testing undergoing either chemotherapy or RT. 40–42,58–65 In general, ques-
tionnaires include questions about the owner’s perceptions of the
Physical Examination pet’s physical state (appetite, sleep patterns, gastrointestinal prob-
lems), interaction with the owner (anxiety, depression, happiness),
Physiologic variables, such as heart rate, respiratory rate, temper- activity levels (mobility, play activity), and perceived pain level,
ature, and pupil size, are not reliable measures of acute periop- in addition to the owner’s level of worry about the pet’s health
erative pain in dogs and are unlikely to be useful in chronic pain issues. 42,60,64,65 Several QOL scoring systems have been created to
states. However, physiologic parameters and the use of comple- evaluate cancer patients; however, the use of nonvalidated instru-
mentary clinical techniques (i.e., imaging and laboratory studies) ments currently represents a source of bias in the measurement