management of chronic/ pathological pain

What is chronic or pathological pain

Pain that outlasts the original injury and expected healing time or lasts

longer than a specified period (??>3 months in humans)

• Changes in central pain processing (hyperalgesia and allodynia)

• Maladaptive

what are the top causes of long-term pain in dogs

1. Osteoarthritis

2. Dental disease

3. Ear disease

4. Vertebral / spinal cord

5. Neoplasia

6. Skin conditions

what are the types of chronic pain

Nociceptive/inflammatory

Neuropathic

Neoplastic e.g. osteosarcoma

Mixed

Referred

Myofascial

Sympathetically mediated pain

myofascial pain

Significant component of many chronic pain states

Under-diagnosed in veterinary practice

Myofascial trigger points – arise due to muscle ‘wear and tear’ = damaged motor end plates = acetylcholine release = local sarcomere contraction = distinct knot or taut band in muscle

Commonly affects postural muscles (neck, shoulders, lumbar and hip girdle)

Detection requires specific palpation technique = often elicits dramatic

response from patient when knot/band is ‘twanged’

May occur secondary to postural strain, blunt trauma, spinal pain (e.g. nerve root impingement, facet joint disease, spondylosis, intervertebral disc disease), osteoarthritis (OA), visceral pain or chronic otitis

implications of chronic pain

Sensory - initially

Emotional – after multiple inputs to limbic system

Cognitive – dog thinks more about the pain/may alter behaviour

Motor - response to above – eg unable to jump up

Welfare and quality of life – animal and owner

‘Suffering’ must be addressed

assessment of chronic pain

Quantitative sensory testing

Force plate analysis - lameness

Validated chronic pain scales:

• e.g. - Glasgow University Vet School questionnaire (GUV-Quest)

• Liverpool Osteoarthritis in Dogs (LOAD)

• Canine Brief Pain Inventory (CBPI)

• Helsinki Chronic Pain Index (HCPI)

• Feline Musculoskeletal Pain Index (FMPI)

approach to chronic pain consultation

Identify owner concerns and expectations

Identify the problem

Assess degree of pain

Classify the components of pain (cognitive/motor etc)

Identify sources of pain and classify type of pain for each source

Identify aims of pain management

Devise treatment plan

Implement plan for review and provide clear outcome measures

what does PLATTER stand for

plan

anticipate

treat

evaluate

return

treatment of chronic pain

A = analgesia

B = bodyweight

C = control of complication, common sense and comfort

D = disease modification

E = exercise

analgesia

Analgesic drugs:

• NSAIDs

• Piprants (grapiprant)

• mAbs

• Paracetamol

• Tramadol

• NMDA antagonists

• Gabapentin and pregabalin

• Tricyclic anti-depressants e.g. amitriptyline

• Others: bisphosphonates, lidocaine patches, capsaicin and cannabinoids

Analgesic interventions (complementary and physical therapy):

• Acupuncture

• Physiotherapy

• Hydrotherapy

• Photobiomodulation (laser therapy)

• Transcutaneous electrical nerve stimulation (TENS)

• Palliative radiotherapy

NSAIDs

Mainstay of treatment for nociceptive/inflammatory pain – particularly

OA

Multiple side effects – GI, hepatic, renal, coagulation etc.

Serum biochemical testing and urinalysis indicated with long term use

grapipant

Non-steroidal, non-COX inhibiting anti-inflammatory drug

• piprant class

PGE2 EP4 receptor antagonist (EP4 receptor involved in development of pain and inflammation)

Recently licensed (2018) for management of mild to moderate pain secondary to OA in dogs

Marketed as first line treatment but may be useful in dogs that do not tolerate NSAIDs

Common side effect: mild, transient vomiting

librela

I see mild injection site pain

Anecdotally owners report PU/PD

Often see an immediate response

• Up to 3 months to improve

Around 50-60% of dogs improve in my clinic

SIDE EFFECTS

solensia

I see skin reactions (itching, skin inflammation and hair loss)

Should not be used in cats under 1 year of age or weighing less than 2.5 kg

Can take up to 3 months = 3 injections

Vital to have good assessment

NMDA antagonists

Ketamine

Amantadine (not licensed in veterinary species)

• Current EU ban

Memantine (not licensed in veterinary species)

• Slow onset (3-4 weeks) for memantine

• Common side effects: transient GI signs

• May cause agitation/restlessness

• May lower seizure threshold

gabapentin and pregabalin

Not licensed in veterinary species

Calcium channel antagonists – analgesic mechanisms not fully understood

Neuropathic pain – ONLY for this type of pain

• How can we be certain?

May be useful in animals that cannot tolerate long term NSAIDs

• Side effects: sedation, vomiting and ataxia (sometimes polyphagia in cats)

• May cause seizures if stopped abruptly

• Renally excreted (care with renal disease)

Pregabalin – oral absorption more rapid and predictable than gabapentin with longer dosing interval but expensive

Concern over appropriate use!

Amitriptyline

Not licensed in veterinary species

Tricyclic anti-depressant

Neuropathic pain with behavioural component

Central opioid receptor activity and serotonin and noradrenaline reuptake inhibitor

• do not use with other serotonin or NA reuptake inhibitors e.g. tramadol

May cause cardiac arrhythmias (ventricular tachycardia and fibrillation) in dogs

Bitter taste = ptyalism in cats

Bisphosphonates

pamidronate or zoledronate for bone pain e.g. osteosarcoma

lidocaine patches

Licensed for postherpetic neuralgia in humans

No veterinary evidence for analgesic efficacy

capsaicin

activates TPRV-1 receptors = initial burning pain = receptor desensitisation

Perineural and intra-articular injections reduce pain and improve mobility in rodent models

Some evidence of anti-pruritic effect in atopic dogs (topical ointment)

Cannabidiol (CBD oil)

ndocannabinoids depleted in chronic disease states and may be involved in development of neuropathic pain

CBD oil can be purchased ‘over the counter’ but designated as a medicine by the VMD

Issues with purity = may contain THC (psychoactive)

Current evidence: adding CBD to NSAIDs in dogs with OA = reduced owner-assessed pain but not vet-assessed pain so better-quality evidence needed before can be recommended

acupunture

Indicated for OA pain, myofascial pain and central sensitisation

Human evidence - stifle OA, chronic lower back pain and migraines

Limited veterinary clinical studies

Generally, well tolerated in cats and dogs without sedation

Analgesic effect depends on patient responsiveness and degree of stimulation (needle size, number of needles, treatment duration etc.)

physiotherapy

To rehabilitate animals and return them to function following surgery, disease or injury

Muscle strengthening and useful for myofascial pain

Includes massage, passive movement, joint mobilization, myofascial release and trigger pointing

Best to utilise trained veterinary physiotherapist

hydrotherapy

Water helps animals to regain strength, fitness and balance – provides

buoyancy and resistance

Joints can be worked and extended without concussive pressure

Various techniques

• Swimming pool

• Underwater treadmill

• DIY (free swimming with owner)

Photobiomodulation (laser therapy)

May be useful in fractious animals that will not tolerate acupuncture or as an adjunct to acupuncture

Limited veterinary evidence for analgesic efficacy – has been used for many painful conditions in humans

Different classes of laser

• Risk of thermal injury and ocular damage (Class IV lasers)

May also be useful for wound healing

TENS

Relies on sensory nerve depolarisation to suppress pain at level of spinal cord – similar to acupuncture

Used widely in humans but may not be well tolerated in animals

Muscle strengthening - rehabilitation/ physiotherapy

Contraindications – cardiac pacemaker, seizures, abdominal area during pregnancy, site of malignant neoplasia

Palliative radiotherapy

Well recognised for palliative treatment of pain associated with osteosarcoma in dogs

Also been shown to be effective for canine OA = reduced inflammation and joint swelling

• Still under investigation using animal models

• Limited availability

• Multiple side effects e.g. long-term tissue damage - including nerve damage) and scarring

• Cannot currently be recommended as a treatment for OA

bodyweight

Obesity is common in animals with OA

Obesity = chronic, low level inflammatory state

• adipokines can exacerbate OA

Moderate weight loss (up to 10%) can reduce pain scores and improve quality of life in animals with OA

Control of complications, common sense and comfort

Owner compliance improved if they are aware of potential side effects and complications of treatment

Involvement of the owner in the management process e.g. teaching appropriate massage techniques that can be performed at home = improved compliance and owner satisfaction

Common sense and comfort = environmental modifications

• optimisation of core territory is essential for cat welfare

environemental modifications - dogs

Ramps for vehicular access

Non-slip rugs/mats on laminate flooring

Restriction of upstairs access

Raised food and water bowls

Carts to allow rest periods during walks

Supportive bedding

environmental modifications - cats

Use of steps/ramps to allow access to heights/favourite areas

Provision of new hiding places

Raised food and water bowls and ensure easy access to these resources (ideally different rooms)

Modification of cat flaps/outdoor access

Introduction of new games to adapt play behaviour

disease modification

Correct diagnosis (blood testing, diagnostic imaging, arthrocentesis etc.)

• Specific medications e.g. corticosteroids for IMPA

• Surgical intervention e.g. arthrodesis or joint replacement

Polysulphated GAGs, pentosan polysulphate and hyaluronan injections

• Potential chondro-protective and chondro-regenerative effects

• Inconsistent results reported in literature

‘Nutraceuticals’

• Omega-3 fatty acids e.g. green-lipped mussel √ √

• Elk velvet antler √

• Palmitoyl ethanolamide (PEA)

• Glucosamine/chondroitin

• Turmeric

• Hydrolysed collagen

exercise

Strict rest only for acute conditions (e.g. post surgical or OA flare up) or

those where pain is exacerbated by exercise

Rest = first step of rehabilitation process

Exercise useful for weight loss and muscle strengthening

Emotive component

Restricted exercise should be varied to provide stimulation

Ask owners to video their animal’s exercise

Use of appropriate harness

Modification of exercise e.g. scent training

horses

Many conditions = chronic pain e.g. OA, laminitis, impinging dorsal spinous processes (DSPs) etc.

Recognition challenging (prey species)

• lameness, reduced appetite, weight loss, reduced interaction with owner, changes in facial expression etc.

Surgical intervention e.g. neurectomy and fasciotomy for suspensory desmitis, DSP resection

Holistic approach recommended

Physiotherapy

Acupuncture

Weight management

NSAIDs

Ketamine CRI (sub-anaesthetic doses) – limited evidence

Paracetamol – laminitis and compartment syndrome

Gabapentin – laminitis and neuropathic pain

Tramadol – limited evidence

Soluble epoxide hydrolase inhibitors e.g. t- TUCB – laminitis

Continuous peripheral nerve blockade (local anaesthetics)

food producing animals

Chronic pain likely under-recognised but exists (e.g. chronic lameness in dairy cattle, footrot in sheep etc.)

Recognition very difficult (especially prey species)

• locomotion scoring, changes in appetite, reduced productivity?

Limited licensed pharmaceutical options:

• NSAIDs

• Paracetamol (licensed in pigs)

• Ketamine – licensed for sedation and GA

• Cannot use opioids

Consider withdrawal periods

‘Pet’ ruminants, camelids or pigs may not enter food chain but still subject to the same drug regulations

Acupuncture

Weight management – especially rams, bulls and pets