Management of IHC
Currently, there is no known cause of Feline Idiopathic Hypercalcemia (IHC). However, experts know that feeding dry food with its inherently low water level, causes the kidneys to concentrate the urine. This concentrated urine contains minerals such as magnesium and phosphorus which may produce struvite crystals (stones) that can lead to urethral blockage in the cat. This condition is deadly.
When this condition became prevalent, pet food companies decided that the urine was too alkaline (perfect environment for struvite crystals to grow) and decided to add an acidifier and reduce the amount of magnesium in the typically dry food. The acidifiers that are commonly used are ammonium chloride or dL-methionine and some companies use phosphoric acid or sodium bisulfate. However, while struvite crystals became less prevalent in the following decade, calcium oxalate crystals became more prevalent (1990's). These crystals grow in an environment that is too acidic.
Many experts now believe that acidifying, magnesium-restricted diets lead to IHC in genetically predisposed cats, perhaps due to the calcium resorption from bones. It is interesting to note, that carbohydrates produce an alkaline (basic) urine in the cat while meat protein produces a slightly acidic urine (pH 6.5) which is the natural pH of cat urine and has the higher magnesium level required by felines [Funaba et. al. 2003].
There is also some indication that the acidosis that occurs due to feeding acidifying diets, may also be causing kidney failure with or without hypercalcemia [Purina Nutrition Forum 1998]. Acidifying diets may also play a role in Feline Oral Resorptive Lesions (FORLs).
At least one researcher theorizes that high levels of Vitamin D may be at fault, especially in kittens fed a high Vitamin D and high calcium diet. Unfortunately, scientists do not know exactly how much Vitamin D is required by cats in their daily diet.
Loss of appetite, lethargy, mild weight loss, and constipation may be some of the signs associated with IHC. Typically, most cats with mild to moderate IHC show no signs at all.
A change in diet is warranted with the discontinuation of an acidifying diet, if one was being fed, and many experts suggest orally administered glucocorticoids or both. Diets should be wet-only to promote urinary dilution. Diets that are low-fat and high-fiber have been used with the idea that the fiber will reduce the availability of the calcium for intestinal absorption (Hill's Prescription Diet w/d - Midkiff et al.). This diet has has been proven to be helpful with only some cats and ionized calcium will typically rise again after some time.
There is evidence that a wet-only diet of high meat protein without dL-methionine or other added acidifiers may help some of these cats. Moving toward a more natural species-appropriate diet may help the majority of the cats diagnosed with IHC, particularly the mild form. Since, as of date, there is no known mechanism to help resolve or control IHC in most of these cats. So far, research of dietary changes have not included this type of diet. Further studies are warranted. Read Dr. Mark E. Peterson's suggestions.
In lieu of a high-fiber diet, some cats that are diagnosed with IHC may be given a canned/raw only diet. The diet should consist of high-meat protein, moderate-fat, and low-carbohydrates. Magnesium levels do not need to be reduced and acidifiers should not be used. Cats may become starved for protein and fat on high-fiber diets which may also cause constipation. Suggested high-protein, grain-free canned foods are Wellness, and Nature's Variety. Nature's Variety also produces a quality raw food. The Wellness varieties of Beef & Chicken, Chicken, and Turkey have the lowest amount of calcium in them (as acquired from Wellness).
Adding some raw or cooked chicken meat will also help raise the protein level of the food without increasing calcium content. However, make sure that only small amounts (less than 10% of your cat's daily caloric intake) are fed, as the meat is not properly balanced since it does not include calcium and other nutrients derived from bone and organs. All other "treats" should be removed from the diet and fresh water should be available at all times. Feeding meal times instead of "free choice" may also help the body with control of calcium levels and urinary pH.
Remember to seek out your veterinarian's advice before attempting any diet change. For more information on switching cats over to a canned/raw diet, please see the Feline Nutrition Awareness Efforts' website.
Corticosteroids (a steroid hormone produced by the adrenal cortex) promote reduction of serum calcium concentration by reducing bone resorption (reabsorption), decreasing intestinal absorption of calcium, and increasing renal excretion of calcium in the urine. Prednisone is used at 5 - 12.5 mg/day and may produce a partial or complete reduction in serum total or ionized calcium concentration during treatment. However, this increased excretion of calcium may lead to greater likelihood of calcium oxalate urolithiasis (bladder stones). A wet-only diet must be used to promote dilution of urine. Administering steroids over a prolonged period of time also has damaging effects on the body so the doctor and owner must weigh the benefits of sustained use. According to Dr. Elizabeth Hodgkins, cats that are fed a dry, high-carbohydrate food tend to have some level of liver dysfunction when on corticosteroids, however, on wet, high-meat-protein foods, this does not typically occur.
Bone Resorption Inhibitors & Alkalinizing Agents
|diphosphonates||inhibits bone resorption|
|calcitonin||inhibits bone resorption|
|mithramycin||inhibits osteoclastic bone resorption|
|sodium bicarbonate||decreases serum calcium by alkalinizing blood, thereby shifting the ionized calcium into protein bound calcium, which is less harmful|
|potassium citrate||decreases serum calcium by alkalinizing blood, thereby shifting the ionized calcium into protein bound calcium, which is less harmful|
The FVRCP combination vaccine is for Feline Viral Rhinotracheitis, Calicivirus, and Panleukopenia. Rhinotracheitis and calicivirus cause upper respiratory infections while panleukopenia (feline distemper) is deadly, most particularly to kittens. However, the cells used to grow the viruses to create the vaccines are from cat kidneys. When these kidney cells are injected into the cat (along with the vaccine), the immune system views them as foreign and makes antibodies against them, this is how vaccines work. Unfortunately, those antibodies don't know the difference between the injected kidney cells and the cat's own kidney tissue resulting in an autoimmune attack on the cat's kidneys. This can lead to inflammation and permanent damage in some cats.
Prednisone is used to suppress the immune system and reduce inflammation. It is also prescribed for FIHC cats to promote reduction of serum calcium concentration. However, with the immune system already weakened due to steroid use, injection of the Rabies vaccine may further weaken the immune system and/or fail to provide immunity. Many adverse side effects can follow vaccination immediately or up to 45 days after the shot, says Jean Dodds, DVM, and can cause minor symptoms, such as swelling at the injection site, and life-threatening conditions such as seizures, and liver and kidney damage. For those living in areas that by law require the rabies vaccine, your veterinarian may provide a vaccine waiver for you to use to register your cat legally without administration of the vaccine.
Unhealthy animals should never be vaccinated. Before vaccinating an FIHC cat, discuss with your veterinarian the need, especially when the affected cat may have smaller than normal kidneys and/or kidney disease or one that is being administered steroids.
Over time, the excess calcium will deposit in the kidneys and other organs and soft tissue. The damage to the kidneys may eventually lead to renal failure. With successful management of IHC, kidney failure may be delayed indefinitely. If, or when, kidney failure does occur, there are ways to manage it as well. Please see the Feline Chronic Renal Failure website for more information and support. You may also want to check out FNAE's information on a new way to manage cats with renal disease/failure, that is proposed by Dr. Lisa Pierson and renal disease control by Dr. Elizabeth Hodgkins.
Many cats may lead happy normal lives for many years after initial diagnosis depending on their calcium levels, management of IHC, and management of renal failure, should it occur.In summary:
- IHC cats should be fed a wet-only diet with no acidifiers
- a high-quality, canned or raw, high-meat-protein, moderate-fat, low-carbohydrate, grain-free diet should be tried
- diets comparably lower in calcium then others should be used - contact manufacturers for values
- adding a small amount of chicken muscle meat (raw or cooked) will increase protein without increasing calcium content
- feeding meal times instead of free choice may help the body with control of calcium levels and urinary pH
- medications can be added if the above does not produce sufficient or lasting results
- without successful management, IHC may lead to kidney damage and renal failure but this may also be managed for some time