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An Internists Perspective

Ah yes, the prednisone treatment trial.  Steroids have an important role in treating a wide range of disorders.  They are inexpensive and can be life saving for some owners.  So when should steroid trials be considered and when can they really become dangerous?  Really any time I am reaching for steroids without a diagnosis I am considering any disease that can be made worse by steroids, the part of the body being treated, and of course the dreaded lymphoma diagnosis.  The two single-most (relatively) common dangerous diseases we can guess wrong for a steroid trial are lymphoma if a client would at all wish to treat with chemotherapy and in our part of the country, histoplasmosis. 

Lymphoma of course is one of the more challenging diseases to diagnose after starting steroid therapy.  This is true for large cell lymphoma as well as small cell lymphoma.  I have had both cats and dogs get endoscopic biopsies after having failed or partially responded to steroid trials only to keep getting a diagnosis of inflammation and later find lymphoma on the necropsy floor.  Sadly, there are no guarantees for stopping steroids and being able to obtain a diagnosis.  Response to chemotherapy will often be less compared to if steroids and chemotherapy are started at the same time.  I have even seen dogs go into complete remission for multicentric lymphoma from a single dose of prednisolone eye drops.  There are no real rules other than all owners should have a discussion regarding chemotherapy prior to starting steroids if lymphoma is at all possible.  Remember that finding mild thickening of the muscularis layer of the intestines in cats on ultrasound can be inflammation, small cell lymphoma, or histoplasmosis.  Some radiologists do not provide all these differentials, but they can and often do look identical.

Histoplasmosis is another one that can become a problem.  In particular, because the patients can feel better for a couple of weeks so there is a false sense of security.  Then the histoplasma becomes much worse and the patient becomes much more ill.  This is especially devastating in animals getting depomedrol for presumed lung diseases.  I have seen some cats require oxygen cage therapy for 3 weeks or longer after getting depomedrol for presumed asthma who actually had pulmonary histoplasmosis.  Daily oral steroids are easier to remove if there is an issue, so are always preferred when possible, for empiric treatment trials.  Also from a gastrointestinal disease standpoint, I find depomedrol rarely is a helpful steroid even with inflammatory bowel disease.

Addison’s disease can be tricky to diagnose once steroids are started if an ACTH stimulation test was not performed.  We are taught that dexamethasone does not interfere with an ACTH stimulation test.  Technically, this is true if the test is performed quickly enough because dexamethasone will not read as cortisol on the assay.  However, remember that we use dexamethasone for suppression tests, and it will interfere with the hormone axis.  When in doubt, if possible, try to obtain and hold post cortrosyn serum.  There are ways around this in the future, but it is ideal to have an accurate diagnosis prior to lifelong therapy.  The easiest way to have an unclear ACTH stimulation test is to perform it the day after dexamethasone is started.  However, Addison’s can be life threatening so this is a situation where I would still recommend treatment if an owner cannot afford testing. 

Nasal disease tends to only partially respond to steroids.  The biggest downside to a steroid trial for these patients is the rare lymphoma or fungal cases.  Inflammatory lung diseases tend to respond very well to steroid therapy.  For these cases if owners cannot afford lung or nasal sampling, there is a lower relative risk with steroid therapy.  In these cases, unless the disease is very chronic and very stable, I always offer histoplasma urine antigen testing to be safe.

There are many times where steroids are used empirically without a diagnosis.  And many animals who will have their lives saved with this therapy.  It is just important to have these discussions prior to committing to such treatment.  Creating a handout can be helpful that can bullet point pros and cons of steroids without a diagnosis.  I often will have clients sleep on it or discuss with family members prior to committing to therapy without a diagnosis.  This is to be sure we are all on the same page for what is best for each individual family and patient.


Crystal Hoh DVM, MS, DACVIM

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