Pain in animals part 1: what is pain?

Pain. Everybody knows what it feels like, and – apart from a few determined individuals – we tend to avoid it. But what is it? The International Association for the Study of Pain (IASP) defines it as:

“an unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage.”

Or, in other words, when you damage yourself it hurts. And if you’re feeling down already, it hurts more. And if you’re not feeling down already, then pain may make you feel down. And then it will hurt more.

The IASP mainly looks at pain in humans, but it’s a long time since we stopped trying to pretend that animals either don’t feel pain like we do, or else don’t get upset about it. They do, and their inability to communicate pain effectively (or else our inability to properly listen) means that for a lot of animals, pain is a chronic, miserable constant in their lives, despite help being close to hand.

There are tiny pain receptors all over the body, inside and out, attached to nerve fibres. When a tissue is damaged, they’re triggered to send impulses up to the brain, which senses them and registers the feeling we call pain. Hard to describe, but we all understand what it is and we’ve all got experience of it. Pain receptors are usually well embedded in tissues, and usually need a fair bit of triggering – otherwise, any form of touch would be painful.

When we describe pain in ourselves, we often use terms like sharp, jabbing, dull or throbbing, and they can give an indication of how bad it is. But in a more fundamental sense, we differentiate into two types: physiologic and pathologic.

Physiologic pain is ‘protective’ – it’s the pain we get when picking up a hot pan. Very quickly, the body registers the ‘ouch’ and the pan is dropped, hopefully before too much damage is done. Without this kind of reflexive response, we’d just keep on holding the pan until our hands were badly damaged.

Physiologic pain, more or less, is our friend.

Pathologic pain, on the other hand, is the pain that comes from existing damage, such as a broken leg or a arthritis. Whilst it can initially be useful to draw our attention to the condition, it becomes debilitating quite quickly and can be a problem in its own right. It’s this kind of pain that we need to deal with in our patients: the pain that is ever-present or recurrent, at whatever level. If we don’t, the pain becomes responsible for stress, depression and a reduced quality of life.

For example, the pain of arthritis can actually make the condition worse:

1. being unwilling to move around makes the joints stiffen up through lack of use
2. lack of exercise piles on the weight, putting more pressure on the joints
3. increased pressure on the joints means more pain, so less movement, more stiffening and more weight gain

A vicious cycle is created where the problem becomes worse and worse under its own steam – and pain is as the root of it. Whilst we can’t cure the arthritis itself, by removing pain and getting our patients moving we can reverse the stiffness and get some weight off.

Pathologic pain can have its uses, but isn’t always our friend.

How do we recognise pain?

In order to be able to keep our pets out of pain, we must be able to recognise the signs of pain. Remember, though, that absence of signs doesn’t guarantee that there’s no pain – if in doubt, assume it’s there.

Understanding how a pet feels depends on a number of things:

• Empathy
• Understanding of normal behaviour
• Observation

Some owners are just better at spotting pain. Some patients are better at showing it. But unless we look for it, we’re never going to find it.

Dogs tend to be the easiest patients in which to spot pain: their outward responses to pain are more similar to ours than for most species. They’re designed for pack-living, and their conditioning in our homes makes them more likely to be willing to show pain to us, and even to seek help with it. I have, over the years, seen a small number of ‘malingerers’ who were hopping lame at home, but completely normal when away from their owners – generally because being hopping lame at home meant cuddles and treats and all things good.

Do beware, though, of behavioural changes as the only signs of chronic pain in dogs. When our collie, Juno, was a younger dog, a combination of being overweight (yes, shame on me), hip dysplasia and the appearance of screaming toddlers with grabby hands made her mildly aggressive – which, for Spoony, was so out of character that it was immediately apparent. Early recognition of the central issue, along with pain control measures (weight loss, acupuncture, educating the kids) sorted it all out quickly.

Cats are different, very different. When in pain, they tend to isolate and may just become distant and/or grumpy. There may be aggression towards inanimate objects, or self-directed as overgrooming to the point of self-harm, and accidentally touching the sore spot will usually lead to bloodshed, none of which will be the cat’s. But cats are relatively worse at expressing pain in other ways which are immediately recognisable. Drop in food intake is, though, a classic sign of pain in cats.

Rabbits and other herbivores (traditionally, the prey animals) can be very difficult to recognise as being in pain. Their entire survival in the wild depends on not looking weak – predators will tend to go after the stragglers first, to reduce energy expenditure and risk in obtaining food. Survival in the wild depends on being invisible as a target, so hiding signs of pain is standard in these patients. Sometimes, you have to look very hard to find it, which doesn’t mean that the pain isn’t significant. It’s entirely connected that these are the species whose general welfare gives us the most worry.

General signs of pain in animals include:

• Reduced mobility or abnormal movement – if it hurts to move, pain is reduced by not moving. Equally, if a pet is moving in an odd way, then it’s because moving in a normal way hurts. A major, major problem that we encounter is the attitude that reduced mobility is a normal part of ageing – so pain is often not recognised in older patients. It’s amazing what a trial on painkillers can do to change minds.
• Guarding and defence – hiding away or trying to protect the bit that hurts. A common entry on clinical notes is ‘guarding the abdomen’ which usually relates to a tenseness in the belly when we’re trying to palpate.
• Inappetance – most animals will either eat less or stop eating altogether when in pain. When the pain is settled, we often see rebound eating, where intake is increased for a while. This can be a cardinal sign for assessing response to treatment.
• Adipsia or polydipsia – most animals will also drink less, although some, often as a response to stress, will drink too much. Patients with abdominal pain will often swallow great bowlfuls of water, possibly because of a temporary soothing effect.
• Altered interaction – many animals will hide away and reduce their interactions with other members of the household; others, particularly dogs, will become more needy and seek more interaction. Normally friendly relationships may explode into world war three and, rarely, vice-versa. It’s not so much how the interactions change, but that they change in the first place.
• General distress – other signs of distress include increased breathing rate, increased pulse rate, abnormal breathing (cats DON’T pant as a normal behaviour), vocalisation (howling, mewing, whimpering), a certain glassiness of the eyes, hunched body position, bubbling at the mouth (reptiles), fluffing of the feathers or over-stimulation and anxiety from normal noises and events.

Even allowing for all of these symptoms, pain can be a vague and difficult thing to spot. One of our classic presentations in the consult room is ‘S/he’s just not right’, where a patient just isn’t him- or herself. It’s astonishing how many of these patients have some kind of pain complex, and full marks from me to any owner who can spot when their pet is just not happy, however subtle. Nothing ever happens for no reason, and absence of any particular symptom in a depressed patient should always trigger suspicion of pain as a cause.

What factors make pain worse?

Inflammation is a big one. Inflammation is the swelling you get around, say, a cut or a sprain. It’s also the reason why a sprained ankle tends to hurt more the next day than it does at the time of injury. Inflammation is the body’s reaction to detecting damage and is its way of drawing the immune system in to start repairing things. Once damage is detected, a sequence of events is triggered called the inflammatory cascade, which goes a bit like a line of dominoes – once started, it takes on a life of its own. The end result is the release of a lot of chemicals which promote blood flow into the area and, importantly here, an increased sensitivity of the local pain receptors so that almost any pressure sets them off.

A good illustration of this is to imagine someone poking you lightly in the arm. For most of us, it’s not painful, just annoying (and strangely familiar for those with brothers and sisters). However, if you’d been to the doctors for a jab earlier in the day, suddenly the touch is extremely painful. The inflammation around the injection site has switched all the pain receptors on to the point where even light pressure sets them off. This phenomenon is at the heart of much of the chronic pain that our patients suffer from, with conditions like arthritis. Drugs which try to stop the inflammatory cascade are called anti-inflammatories.

Other things that make pain feel worse are:

• The amount of time that it’s been going on for – most of us are fairly stoic, at least at first, but sooner or later an inability to get comfortable, to sleep, to do the things we want to, all start to get us down. It’s the same for our pets.
• Having more than one painful bit – two plus two in this case tends to make five.
• Previous experience of pain. Our pets have a phenomenal memory for pain, which translates to a fear of repeating the experience. Pain at the vets can put a patient off us for life, which is why we try to make the first couple of visits as stress-free as possible.
• Being in a bad mood already. If you walk down the street on a happy day and stub your toe, it hurts. If you’re already in a bad mood, the world seems to cave in. This is where the vicious cycle of pain and depression starts to bite: being in pain causes stress and depression, and stress and depression make pain feel worse.

Pain control is one of the most progressive aspects of veterinary medicine, which means that pain in our pets is no longer acceptable. It might not always be possible to get right on top of it, but that doesn’t mean we should ever be happy about it – and there are now so many available treatments that giving up is simply not a reasonable option.

In the next instalment, I want to discuss the various drugs that we can use in dealing with pain in animals, and how they might fit together. After that, we’ll briefly go on to integrated (non-drug) treatments and how they can make all the difference to some patients.

If you are worried about any symptoms in your pet, please talk to your vet or use our Interacitve Symptom Guide for advice on how urgent the problem may be.