Dear Dr. Jody: Our six year old golden retriever, “Honey”, has just been diagnosed with a dangerous form of lupus. What is lupus, and what can we do to help her?
Systemic lupus erythematosus (SLE) is an uncommon condition characterized by massive body-wide destruction of healthy tissues by a faulty immune system. There are several complicated reasons as to why a previously healthy immune system would suddenly turn on its own body and attack it. However, in most cases, we are unable to accurately identify why this deadly disease occurs in each individual patient. Allow me to explain a little Immunology 101.
Imagine antibodies as microscopic Y-shaped structures floating around in the bloodstream. When an antibody spots a foreign invader such as a virus or bacteria, it attaches to the invader (also called an antigen) with the arms of its “Y”.
Like pieces of a jigsaw puzzle, antibodies are usually specific to which antigens they can bind and therefore destroy. This is why disease-specific vaccinations are important. For example, when you get a tetanus vaccination, the bits of tetanus bacteria that are injected into your body have been killed or altered in some way that they cannot actually create the disease. But they still structurally resemble live tetanus bacteria, and so your body churns out antibodies that it has specifically manufactured that match the “shape” of the tetanus bacteria. The antibodies attach to the bacteria and lead to its destruction. Once the “infection” is cleared, there are still some leftover antibodies that hang around in your body indefinitely, so that if you ever step on a dirty nail in a horse pasture and get tetanus bacteria in your bloodstream, the leftover antibodies that have the right “shape” go to work and bind the invading bacteria and lead to its destruction. On a side note, one reason why vaccines fail – as in the case of the ever-changing flu vaccine – is that the disease-causing organism is constantly mutating. The jigsaw puzzle mechanism of the antibody only partly fits onto the newly changed shape of the antigen. Your immune system will be better equipped to fight the infection than if you didn’t have the vaccination, but it may not be effective at completely preventing the disease.
Once an antibody has both of its Y-shaped arms bound to antigens, the entire unit causes a chemical reaction in the body that stimulates the rest of the immune system (there are a lot more players in this complicated process) to destroy the entire antibody-antigen complex, including the kamikaze antibody itself.
In SLE, the dog has somehow developed antibodies against its own tissues. More specifically, it has developed antibodies against nucleic acid, an important ingredient in a cell’s nucleus. And when an antibody binds to the nucleic acid in the body’s cells, it triggers the chemical reaction in which the rest of the immune system destroys the entire antibody-antigen complex: cells, antibody, and all.
Because nucleic acid is everywhere, and because the immune system of an SLE dog is destroying cells that contain nucleic acid, SLE dogs experience destruction of cells in almost every body system, including skin, joints, muscles, kidneys, blood (red blood cells, white blood cells, and platelets), lymph nodes, spleen, lungs, and central nervous system. It’s a terrible disease, and it can be very painful, especially if joints are involved.
Unfortunately the disease can be tricky to diagnose because there is no 100% reliable test for SLE. There are, however, several key tests and physical exam findings that will allow your veterinarian to diagnose the disease with relative confidence. Once the diagnosis is made, the treatment for lupus is usually multi-faceted. Not only do we have to try to shut down the rampant immune system, we need to treat what is wrong in each of the affected body systems. If there is kidney damage, we need medication to make the kidneys feel better. If there is joint pain, we need medication to take away pain. If there is blood cell destruction, we need medication to bring the blood cell counts back up.
One of the most frequently used medications for SLE dogs is prednisone. Prednisone is a steroid that can be wonderful and terrible all at the same time. When used at high doses, prednisone strongly inhibits the immune system. If a healthy individual were to take prednisone, we would be more susceptible to all kinds of infections in the respiratory tract, skin, and gastrointestinal tract, because we have wiped out our immune system. When an SLE dog (whose immune system has gone haywire) takes prednisone, the drug can be fairly effective at halting the immune system’s destruction of the dog’s own tissues. Unfortunately, the side effects of prednisone (massively increased thirst and urination, increased appetite, weakness, continued weight loss, and some risk of developing diabetes) make the drug less than perfect.
If prednisone does not work, there are other drugs that can be considered, but most of them are very expensive. It is nearly impossible to predict which medication will work the best for your dog, and this decision is often a matter of trial and error.
Unfortunately, SLE cannot be cured. At best, it can only be managed. This means that your dog will always have SLE, no matter how successful the treatment is. The disease may go into remission for a while, but will likely flare up from time to time. Some dogs do not respond to treatment and continue to deteriorate. And some dogs experience such severe side effects from the treatment that treatment is not an option. (Remember: the treatment should not be worse than the disease!). There is a relatively poor prognosis for SLE dogs. Sadly, 40% of dogs diagnosed with SLE do not survive more than a year.
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