FOR VETS

THE FMPI—Origins and Features

The Feline Musculoskeletal Pain Index (FMPI) was developed at the Comparative Pain Research and Education Centre at the North Carolina State University (NCSU) College of Veterinary Medicine. One goal of the Comparative Pain Research and Education Centre is to produce valid instruments for the assessment of pain, physical function, and quality of life. These tools are targeted at measuring one or more of the impacts of pain:

1. Pain (adverse sensory and emotional experience)
2. Mobility (the quality of moving freely)
3. Activity (the ability to perform specific activities)
4. Affective Effects (mood, feelings)
5. Cognitive Function

Such tools may be used for veterinary studies evaluating an intervention or treatment; translational studies using naturally occurring disease in animals as a model of human disease; and clinical veterinary patient management. For example, the FMPI can be used to monitor individual feline patients in a practice setting, and also for assessing the efficacy of a new therapeutic to manage chronic pain in cats.

THE IMPORTANCE OF VALIDATION

On the surface of it, a questionnaire seems very easy to produce. However, prior to using such a tool, one must know that it reliably measures what it is purported to measure and that it is able to pick up clinically significant changes in the population in which it is being used. This is the process of validation.

The process of validation is thus an important one, and consists of several stages:

• Item generation: The generation of the questions to be tested needs to be carefully undertaken, and have input from appropriate stakeholders.
  • Using patients (painful and healthy populations)
  • Using focus groups
• Readability: It is important that the instrument be easily understood by those using it.
• Reliability: The stability of a tool examines the reproducibility of the tool administered on different occasions. When the tool is a questionnaire, its internal consistency is based on a single administration of the tool and represents the average of the correlations among the questions in the tool. Both internal consistency and stability must be proven before a questionnaire is to be deemed reliable.
• Validity
  • Face Validity indicates whether, on the face of it, the tool appears to be assessing the desired qualities
  • Content Validity refers to a judgment regarding whether the tool covers all of the relevant content
  • Construct Validity refers to testing that is used when the tool is measuring something (a construct) that cannot be directly observed (pain, quality of life, etc.). While the construct cannot be directly seen, behaviors resulting from it can be observed. Obviously, it will be impossible to “prove” that something that cannot be measured directly is being measured. Several approaches can be used:
    • Hypothesized factors tested with factor analysis
    • Discriminatory Validity: Does the instrument discriminate between healthy animals and those with musculoskeletal pain? Does it discriminate between different severities of the condition?
    • Responsiveness of the tool to a treatment known to change what is being measured (e.g., arthritis pain), or to a change in the condition over time
    • Correlation to overall quality of life
  • Criterion or Concurrent Validity refers to, How well the instrument correlates with some other measure – a measure accepted as the “gold standard.” Often, in the development of subjective assessment tools, the best approach is to use an accepted objective measure. Because pain cannot (yet) be directly measured, a surrogate objective measure can be used, e.g., objective measurement of activity as pain is expected to impact activity. However, it must be remembered that pain impacts many different dimensions, and the changes in different dimensions with pain, and with pain relief, are not always of the same magnitude. Therefore, caution has to be used when using even an objective measure of one dimension to assess another dimension.

JOINT PAIN IN CATS

Arthritidies are common in companion animals, and joint pain, particularly associated with osteoarthritis (OA), is common in companion animals such as dogs, cats, and horses. It results in impairment in mobility and performance of activities and is associated with spontaneous and induced pain.

In pet dogs, osteoarthritis is a common condition probably affecting two fifths (40%) of the population. In pet cats, radiographic evidence of OA/degenerative joint disease (DJD) is apparent in up to 90% of all cats (Lascelles et al 2010), with an estimated 50% of these having clinical signs of impairment due to joint pain, such as changes in mobility, particularly gait, jumping, and use of stairs (Klinck et al 2012). Other painful degenerative joint diseases such as the immune-mediated arthropathies occur in dogs and cats, but less frequently than the inflammatory arthropathies (such as rheumatoid arthritis) in humans.

DIAGNOSING JOINT PAIN IN CATS—ETIOLOGY AND PATHOPHYSIOLOGY

In contrast to humans, OA in dogs is mainly due to developmental orthopedic diseases—hip dysplasia, elbow dysplasia, osteochondrosis dissecans, non-traumatic cranial cruciate ligament degeneration—and so is considered an early onset disease and a lifelong disease. The joints most commonly affected are the hip, stifle, and elbow.

Less is known about the etiology of OA in cats than in dogs, but the degenerative disease process appears very similar to that of other species. The joints most commonly affected are the hip, stifle, tarsus, and elbow. For feline synovial joints, there are several recognized and postulated primary and secondary causes of joint degeneration. DJD associated with Scottish Fold osteochondrodysplasia (Malik 1999), mucopolysaccharidosis (Konde 1987), and age-related cartilage degeneration have all been described as primary DJD. Postulated secondary causes of DJD in cats are congenital, traumatic, infectious and inflammatory, nutritional, and immune-mediated, although there is little evidence for many of these causes. Indeed, one of the most common causes of elbow OA in dogs is fragmented coronoid process (part of the developmental elbow dysplasia), but recent evidence indicates this does not occur in cats (Freire 2014). Conversely, hip dysplasia occurs in cats, as it does in dogs, and is similarly associated with OA (Keller 1999).

All tissues of the joint are involved in the degenerative process, and pain is commonly associated with the disease, although, as in humans, pain cannot be predicted by radiographic appearance. Radiography does, however, predict alterations in range of motion (Lascelles 2012). Peripheral and central nervous system plasticity associated with joint pain has been demonstrated in cats (Guillot et al 2014) and is thought to contribute to the overall pain state.

Pain associated with joint disease results in impaired or altered mobility, impaired ability to perform activities, and altered behavior. It is thought to disrupt sleep and impair cognitive function. The multidimensional effects of pain appear similar to the effects in humans.

MANAGING JOINT PAIN IN CATS—CLINICAL SIGNS AND DIAGNOSIS

In clinical veterinary practice, diagnosis is centered on four elements:

1. Owner-reported activity impairment. Owners know their pets’ behavior better than veterinarians do, and veterinarians need to capture this information. This is most easily done by using clinical metrology instruments, such as the FMPI.
2. Observation of resting position, body carriage, and muscle mass.
3. Evaluation of gait and the quality of movement, or performance testing, such as observing fluidity of movement in the room, and ability to jump onto a chair or down from the examination table.
4. Pain on manipulation of affected joints during an orthopedic evaluation, with pain being measured as a behavioral response of varying intensity. Crepitus, decreased range of motion, and joint thickening can be detected associated with the disease of OA.
5. Radiographic evidence of DJD (effusion; osteophytes; subchondral sclerosis; joint-associated mineralization).

Additionally, synovial fluid analysis is sometimes performed. This is infrequently performed unless the clinical picture and examination findings suggest an inflammatory arthropathy, such as an immune-mediated arthritis.

In referral centers or in the comparative research setting, the effects of musculoskeletal pain can be measured by:

• Measuring limb use (kinetic variables measured using force plates or pressure sensitive walkways).
• Measuring spontaneous activity through accelerometry.
• Measuring central plasticity through quantitative sensory threshold testing and measurement of temporal summation and diffuse noxious inhibitory controls.

In clinical veterinary practice, treatment is centered around a multimodal approach:

The dominant approach to treatment of joint pain associated with OA and DJD in cats revolves around medical management, with surgery being used infrequently. The same is true for the inflammatory arthropathies, although there is emphasis by clinicians on detecting and removing the underlying cause if identifiable. Increasingly, confounding co-morbidities are a focus of the treatment of OA, such as obesity management:

• A multimodal drug and non-drug approach is recommended to manage OA and DJD- associated pain.
• There are no FDA-approved drug treatments and only one approved drug in the European Union (an NSAID), though other classes (felinized anti-nerve growth factor and prostaglandin E4 receptor antagonists [piprant], among others, are in development).
• Most evidence exists for efficacy of NSAIDs and dietary modulation through omega-3 fatty-acid supplementation.
• Adjunctive drug therapy is employed, but studies evaluating these therapies are currently lacking.
• Surgical joint replacement is commercially available for the hip, and other custom joint replacements have been performed.
• Non-fatty acid dietary supplements are commonly used, although there is currently no scientific evidence for any benefit in reducing pain.
• Some veterinarians also prescribe the use of non-pharmaceutical anti-inflammatory devices, such as laser, and pulsed electromagnetic field (PEMF) therapies, although scientific evidence of efficacy in cats is lacking.