21 December 2014

Cats: Causes of Chronic Renal Failure

What causes chronic renal failure(CRF) or chronic kidney disease(CKD)?  That is one of the most important questions that remains unanswered in veterinary medicine.  The problem, as I see it, is the cause in one cat may be different from the cause in another cat, which may explain the different progressions of the disease.

A small percentage of cats with CRF have this disease clearly because of genetic problems.  In Persians and related cats, the PKD (polycystic kidney disease) gene goes produce kidney failure due to the growth of multiple cysts in the kidneys which eventually are destroyed by the cysts.  Similarly, amyloidosis is a genetic disease in Abyssinians, Oriental shorthairs, and Devon rexes.

With the exception of genetic problems, the causes of CRF are not clearly known, but there is a list of potential causes.

1.  The after effect of acute renal failure.  Often any type of acute renal failure will scar the kidneys enough that full function is never restored.  With prompt treatment, some of these cats can reach a status where the damage does not lead to more kidney problems.  With others, the damage is too much and the scarring seems to hasten the development of CRF.  This latter group experiences a feedback cycle of lowering kidney function which leads to more stress on the kidneys which leads to lowering the function more.

2.  Immune problem which attack the kidneys.  The main two agents in this category are FeLV and mycoplasma polyarthritis (haemobartonella – feline infectious anaemia).

3.  Infections in the kidneys.  These range from chronic bacterial, to viral (FIP, FIV), to fungal.  Untreated, these infections interfere and then destroy the kidneys’ ability to function.

4.  Cancer.

5. Mechanical problems, such as large kidney stones, granulomas, or even the occasional cyst.

6. Idiopathic – no known cause.  This is, unfortunately, for most cats the ‘cause’ of CRF.   As late as 2 years ago, researchers still had no clear clue as to the causes (and there are probably multiple causes) for the development of most cases of CRF/CKD.  See http://www.ncbi.nlm.nih.gov/pubmed/21262581 

What is interestingly missing from this list is food.  As I will explain in a future post, the moment a cat is diagnosed as having CKD, many veterinarians ask clients to switch the cat to a low protein food.  A few vets and some pet owners have taken this a step further and argued that the protein level in a cat's food should be restricted to prevent CKD from developing.  While researchers have looked into this, there is no scientific support for limiting protein levels to prevent CKD and there are a number of reasons why this could lead to other health problems.

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