By Wendy C. Brooks, DVM, DipABVP
Educational Director, VeterinaryPartner.com
Calcinosis cutis on dog
Calcinosis cutis caused by long-term corticosteroid exposure. Photo by Dr. Carol Foil
Most people are familiar with the term cortisone and may even know that it is a steroid, but while steroids are commonly prescribed to people and animals, much more knowledge than that is not really mainstream. Let's take a few moments to straighten out the vocabulary of steroids hormones so as to understand what is actually contained in that bottle of pills so frequently dispensed.
Steroids produced by the outer area (the cortex) of the adrenal glands. Corticosteroids can be either glucocorticoids (involved with sugar metabolism) or mineralocorticoids (involved in electrolyte balance). We will limit our discussion to the glucocorticoids, as the mineralocorticoids are only used therapeutically to treat a deficiency in mineralocorticoids known as Addison's disease.
This is the natural hormone produced by the adrenal glands to regulate sugar, fat, and salt metabolism in times of stress.
Just another name for cortisol.
A synthetic but inactive version of cortisol.
In order for cortisone to become an active hormone, it must be processed by the liver. The first step in activating cortisone is its conversion into prednisone. Prednisone can be produced in the laboratory and is readily available as a medication.
In order for prednisone to become an active hormone, it must be processed by the liver into prednisolone. Again, prednisolone can be produced in the laboratory and is readily available as a medication.
Adding a methyl group to the predisolone molecule reduces the salt retention effects (thereby reducing the increased thirst side effect. This is frequently desirable for pets as increased thirst translates to increased urination which in turn translates to urinating in the house. Obviously, this would be a side effect to reduce.)
More methylation creates an even stronger steroid with even less salt retention side effects. Dexamethasone can also be manufactured in the laboratory and is readily available as a medication.
Further modifications of the cortisol molecule can create steroids that last for a prolonged period (methylprednisolone acetate), or that are more water soluble (prednisolone sodium succinate). These further modifications are generally for the injectable products while those listed above are oral.
There has never been a class of drug that has more application in disease treatment than glucocorticoids. Indeed, this group is rivaled only by antibiotics in lives saved.
That said, side effects from the glucocorticoid group are numerous and can be classified into those seen with short-term use and those seen in long-term use.
Short-Term Side Effects
A pet taking glucocorticoids is likely to experience the following:
- Increased hunger
- Increased thirst (and possibly urinary incontinence if there is inadequate access to an area for appropriate urination)
- Panting (dogs)
- Hard plaques of diseased skin called calcinosis cutis; this is calcium deposited in the skin.
- General loss of energy
- Hidden infection being unmasked.
Furthermore, pre-diabetic animals may be tipped over into a diabetic state with steroid use. Often in these cases, the diabetes resolves once the steroid wears off.
A similar situation exists for patients with borderline heart failure (a situation for which cats are notorious). The extra salt retention from steroid use can prove to be just too much for a heart that can barely manage its normal fluid volume. The salt retention causes fluid retention and a borderline heart may not be able to manage.
If inconvenient side effects become problematic, adjusting to a lower dose of medication frequently solves the problem. The goal with glucocorticoids is always to find the lowest dose of medication that is still effective. For more serious side effects, a medication of a different class may be needed.
Long-Term Side Effects
Latent urinary tract infections in up to 30 percent of patients. Monitoring for these is necessary with periodic urine cultures. The patient will not have the usual symptoms of urinary infection as the steroid will suppress the associated inflammation. Culture may be the only way to detect the infection. There are many conditions that require long-term suppression of the immune system. Glucocorticoid doses generally include an anti-inflammatory dose that is lower and an immune suppressive dose that is higher; when used long enough, lower doses will suppress the immune system. When steroid use stretches out for more than 4 months, a new set of side effects (in addition to those listed above) becomes of concern:
- Developing thin skin, blackheads, and poor ability to heal wounds or grow hair
- Developing obesity and muscle weakness
- Hard plaques of diseased skin called calcinosis cutis. These plaques are deposited calcium in the skin.
- Predisposition to infection of any kind, weakening of immune defenses
- Developing Cushing's syndrome
All of the above listed effects can be seen and can be considered symptoms of this syndrome.
When long-term therapy is needed, monitoring tests become important; requesting refill after refill without regard for the potency of these medications is not appropriate. Periodic urine cultures and even blood testing is part of responsible on-going corticosteroid use. For details on what tests are best for your pet, consult your veterinarian.
When a long-term dose of steroids is deemed to be excessive, it's time to seek another medication so as to spare the amount of steroids needed if not replace it altogether. There has recently been a proliferation of medication for itch relief without the use of steroids. For alternative immunomodulating drugs, consult your veterinarian.