Feline Osteoarthritis: Etiology & Symptoms (part 2)

OA & DJD

Osteoarthritis (OA) is a type of degenerative joint disease that is clinically characterized by a gradual and progressive development of joint pain, stiffness and limitation of joint motion.
Pathologically it has been considered a non-inflammatory disorder of moveable (synovial) joints characterized by deterioration of articular cartilage and consequentially by new bone formation at the joint surfaces and margins.
OA is often referred to as a non-inflammatory disease. However, the dichotomy between inflammatory and non-inflammatory/degenerative arthritis is becoming less clear.  

Degenerative joint disease (DJD) is often used incorrectly to describe the same as OA.
DJD is an umbrella-term that includes all types of degenerative pathology in any type of joint. For example, DJD includes OA but also isolated degenerative lesions such as enthesophytes, isolated degenerative soft tissue mineralization within joints not related or secondary to OA (for example: mineralization of menisci or ligaments), spondylosis deformans of the intervertebral disc (non-synovial) joints and arthritis secondary to joint trauma.

Etiology
Feline OA is most commonly primary or idiopathic, which means that there is no obvious underlying cause for the development of the disease. While Secondary Feline OA is where the disease is associated with existing joint pathology.
Other underlying causes of secondary feline OA include mucopolysaccharidosis, medial patellar luxation, cranial cruciate ligament disease, acromegaly, developmental luxation of the radial head, and other arthropathies.
Breed predisposition to certain pathologies should be taken into consideration.
Main Coon cats are prone to hip dysplasia and therefore high prevalence of hip OA should be expected; the Burmese breed appears predisposed to elbow OA and Scottish Fold Osteochondrodysplasia associated to an inheritable gene mutation unique to this breed.
It is very difficult to confirm or rule out the occurrence of joint trauma during the lifetime of a cat, since repetitive low-grade trauma over a period of time may go unnoticed by the owner.

Risk factors:
The main risk factors for both increasing prevalence and severity of feline OA is the advancing of age and obesity.
The median age of affected cats is 10 years and increasing age is clearly a risk factor for the development of OA and other degenerative arthropathies. 
Obesity in the older cat undoubtedly worsens clinical signs due to the mechanical overload of the diseased joint.
The role of obesity in the pathogenesis of OA is uncertain but is increasingly becoming implicated by contributing to synovial inflammation and chondrocyte damage. Adipose tissue is now considered an important secretory and endocrine gland that secretes many cytokines associated with cartilage degeneration (TNF-alpha, IL-1, IL-6), as well as fat-specific hormones such as leptin and adiponectin which can promote cartilage degeneration.

Clinical signs
A cat affected by OA may present signs such as lameness, stiffed gait, weight loss, anorexia, depression, urinating outside the litter box and poor grooming.
Radiographs and synovial fluid analysis should be performed to distinguish OA disease from other forms of inflammatory arthritis.
Many authors reported inconsistency between clinical signs and radiographic changes, suggesting that lameness may not be a major clinical sign of painful arthritic disease in the cat. 
In effect, it has been shown that most cats present alterations in their behaviour and lifestyle associated with OA, which improved significantly after analgesia. The most significant lifestyle changes were a reduced ability to jump and reduced activity levels.
The study showed decreased mobility (less jumping, decreased height of jump, stiffness and problems walking up and down stairs), less grooming and change in habits and behavior (such as increased elimination directly over the edge of the litter tray) as being associated with OA.
In a subsequent study, an owner questionnaire was used to gather information on mobility, activity, grooming and temperament, before and after the cat was administered a 28-day course of meloxicam. Owners were asked to score their cat’s current lifestyle/ behavior compared with how it was when it was a young adult, and then to make the same comparison after the course of treatment. Owners reported a change in their cat’s behavior and lifestyle over time, and a reverse in these behavioral patterns when pain relief was given; the greatest changes were noted in the activity and mobility of the patients. Changes in jumping behavior are particularly obvious to owners.

Part 3: diagnosis, radiographic features, treatment.

• Questionnaire with examples of behaviors to consider for evaluation when trying to identify cats suffering chronic arthritic pain is available in here: https://journals.sagepub.com/doi/10.1177/1098612X11432828
  

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