Cat - Vitamin A Toxicity

Cats do have a requirement for vitamin A in their diet and deficiency can lead to problems. However, too much vitamin A can also be harmful and this can lead to toxicity.

Signs of vitamin A toxicity

Signs of vitamin A toxicity take a long time to develop and do not usually appear until the cat is quite old or at least middle-aged. The most common problem associated with vitamin A toxicity is a form of arthritis in which new bone develops around joints. This leads to immobility of the joints with stiffness and in extreme cases the joint may become totally fused. A common site of new bone formation is between the vertebrae of the neck which interferes with movement of the neck. Affected cats often have difficulty grooming themselves and the coat may become very unkempt and tatty. In extreme cases the cat is completely unable to move its neck and has difficulty feeding. Limb joints can also be involved e.g. the elbow, carpus ('wrist'). This can lead to lameness and some pain. Owners may notice that the cat cries out when picked up.

Causes of vitamin A toxicity

Vitamin A toxicity is usually caused by eating too much offal, particularly liver and kidney, which contain high levels of vitamin A. There seems to be considerable variability in how susceptible cats are to this problem. Some cats never develop problems even though they may receive liver or kidney in their diet for most of their lives. Other cats seem much more prone to develop the problem. This problem is unlikely to arise in a cat that is fed largely commercial cat diets provided by reputable manufacturers and is associated with feeding home-prepared diets. Some cats develop a particular liking for offal and may eat this in preference to other forms of meat.

Diagnosis

The dietary history usually gives a strong clue to the diagnosis. The new bone associated with the arthritis has a very distinctive appearance that can be recognised on radiographs (x-rays).

Treatment

Once cats have developed signs of toxicity, there will usually be very high levels of vitamin A stored in the cat's liver which will last indefinitely. However many cats will improve if the diet is changed and offal is avoided even though there is little change in the bone which has formed around the joints. Occasionally it may be considered beneficial to remove some of the new bone surgically, but this is not always helpful. In very severe cases no treatment may be possible.