What is amyloidosis?
Amyloid is the term used to describe deposits of fibrils of protein folded in a particular, abnormal way in the cells and tissues.
When these misfolded proteins form an insoluble deposit in an organ in the body — for example, the heart, the kidneys or nerves — the condition is called amyloidosis.
Cases of amyloidosis were first described in humans 350 years ago, but it has only been in the past 20 years that physicians have understood the specific make-up and structure of amyloid protein.
Vet Andy Durham says: “An underlying cause of amyloidosis is usually a chronic inflammatory condition, such as an infectious disease or a tumour — something that triggers the over-production of proteins as the body tries to fight the condition. Sometimes the driving force is obvious, but often the cause is not known. This means there is not a ‘typical’ case of the disease.
“In horses, the spleen is the most commonly affected organ, but it can also impact upon the respiratory tract.”
What are the signs?
Amyloidosis can present in various different ways, but in the first instance there will nearly always be abnormal swellings, abdominal masses and large lymph nodes.
Other signs depend on which organ — or organs — are affected. Affected horses may have difficulty breathing, suffer weakness and weight loss.
Bleeding from the nose usually means that the respiratory system is affected, while if blood is being passed in the urine the kidneys are usually implicated.
When the amyloid protein deposits in the heart, it reduces the heart’s ability to fill with blood in between heartbeats.
This means less blood is pumped with each beat and can lead to breathlessness.
How common is it?
Andy adds: “Amyloidosis is rare in horses. Typically, I would only see one or two cases [at Liphook] a year.
“There is no obvious susceptibility and as far as we know there is no genetic component, however the cases we see tend to be older ponies rather than fit, young competition horses.”
What is the prognosis?
Early identification — and treatment — of the trigger factor for amyloidosis is crucial.
“Once the disease has set in, you would be lucky to be able to reverse it,” says Andy.
“The prognosis also depends on the underlying driving force — something that is, in itself, life threatening, would be impossible to treat.
“In some cases administering steroids can help if the disease is still in its early stages, but it is by no means an exact science.”
Why do we know so little?
There has been little research carried out into equine amyloidois because there is simply not enough case studies to examine.
Andy says: “Equine research tends to focus on young, athletic horses rather than diseases than typically affect older horses and ponies. This, together with the fact that it is so rare, means that there is unlikely to be funding made available for research into amyloidosis in the near future.”
For the full veterinary article on amyloidosis, see the current issue of Horse & Hound (14 July, 2011)