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With summer hopefully well on the way, many of us are spending more time being active, either in the garden, walking or doing more strenuous exercise. This is all good for our mental and physical well-being and I’m sure our pets enjoy the benefits of happier owners. As Tracey and I discovered last week, there is a down-side to a sudden increase in exertion, when muscular effort one day results in significant pain the next (speak for yourself, I hear my wife say!). We walked 20 miles of the Pembrokeshire coast path in 6 hours, a good pace by my standards and even Portia the black Labrador was snoozing by 8pm. She could have had the decency to look a little bit stiff the next day.
The reason I mention this is to follow on from last month when I discussed pain and its control. One of the commonest sources of pain is inflammation and for this reason we use anti-inflammatory medicines to help control it. Acute inflammation is the body’s response to injury and disease and it makes us feel painful and ill, so clinicians obviously have a vested interest in treating it, not forgetting the underlying cause. The mechanism of inflammation is complex and involves chemicals that are released from damaged tissue that in turn stimulate pain receptors and increase blood flow to the affected area. It’s not difficult to imagine why this response has evolved, as the pain discourages further use of the injured part while the increased blood flow starts the healing process but also causes local heat and swelling.
This system works well for relatively minor, acute trauma that affects an isolated part of the body’s tissues and for systemic diseases that are self-limiting, for example, a viral infection. The problems start when the inflammation becomes chronic (ie long-standing) or affects an organ trapped inside a rigid container, like the brain and spinal cord. Swelling inside the cranium is very serious as the brain is compressed, which it really does not like. Depending on the location and severity of the swelling, symptoms can range from personality and behavioural changes to seizures, coma and acute death. Although much more common in human medicine, we do encounter increased intra-cranial pressure in dogs and cats, often as a result of trauma or as a congenital defect (hydrocephalus and breed-specific cranial deformities). There is another organ that cannot tolerate inflammation and its been a topic of conversation over the last couple of years; the lung. Just a tiny amount of extra fluid in the lung prevents the exchange of oxygen with carbon dioxide and this is how certain viral infections can be fatal (don’t we all know). It’s not the virus per se that’s the problem, it’s the body’s response. Non-steroidal anti-inflammatories are not powerful enough for serious cases of lung inflammation which is why the use a potent steroid, dexamethasone, is considered.
I mentioned the complexity of inflammation and through the clever techniques developed by molecular biochemists, we now know the sequence of events. Pivotal to the inflammatory response are a group of fatty molecules called “prostaglandins” (PGs). Named after an exclusively male genital gland (guess which one!) this diverse group of hormones orchestrates inflammatory responses. Non-steroidal anti-inflammatories (nsaids) like meloxicam (widely used in human and veterinary medicine) reduce the production of PGs and so reduce inflammation and hence pain. But it’s never that easy. Some PGs are really helpful, maintaining blood flow to many parts of the body, e.g. gut, kidney and many other tissues and these helpful PGs are affected by nsaids along with the pain-producing PGs. That’s why long-term nsaid use comes with a risk i.e. ulceration of stomach or intestine and reduction in kidney function. Having said that, these medicines are used safely millions of times a day in both humans and animals and can provide significant pain relief without any problems.
Most of the above applies to acute inflammation but like pain, inflammation can become chronic. The healing process becomes long-standing in an attempt to finish the job but the destructive element of the inflammatory process prevents this. What results depends on the part of the body affected but many of us are familiar with the effects of chronic joint inflammation. Here, joint surfaces are damaged, scar tissue causes permanent thickening and new bone is formed around the joint (osteoarthritis). This is an area where inflammation meets degeneration, a very unfortunate part of getting older for us and our pets. The point is, chronic inflammation makes the degenerative effects of ageing worse and clinicians should not lose sight of this. So no matter how old your dog or cat is, treating inflammation can be beneficial, not just to reduce pain but also to slow down the effects of the advancing years.