When the Brain Becomes Inflamed

Early diagnosis and aggressive treatment can control encephalitis

BY DAYNA GARNEAU

Veterinary medicine has progressed to a level where surgeons can manipulate nearly every body system. They can remove large parts of diseased liver, excise lung lobes and trans-plant kidneys. But they face a major challenge in neurology. The central nervous system is the body's control center, and small changes in it can result in profound effects. Infections and immune system disturbances can affect brain tissue, causing inflammation, or encephalitis, which may be accompanied by swelling and abscesses.

The disease occurs in nearly all species. Although its incidence among dogs is low, a genetic predilection exists for small dogs and toy breeds, especially Yorkshire Terriers, Pugs, Maltese and Chihuahuas. Because the disease can progress rapidly and lead to death within days, it's important for all owners to recognize the symptoms. Most are readily noticeable and should send up major alarm flags: lethargy, tilting of the head, disorientation, walking in circles, blindness, stumbling, dullness and seizures. Owners should know, too, they can control the disease with early diagnosis and aggressive treatment.

30 Cases Annually

"In the neurology department, we see around 30 cases of encephalitis per year," said neurologist Dominik Faissler, DVM, at the Cummings School of Veterinary Medicine at Tufts University. "It is difficult to predict the prognosis of these cases ahead of time, but a significant response to treatment over 72 hours is a good indication that the pet will pull through."

Diagnosis itself may prove daunting because the symptoms can mimic other neurological diseases — strokes and tumors might cause similar signs. In some cases, veterinarians may never be able to uncover the exact cause.

Most signs should send up major alarm flags — lethargy, blindness, seizures.
Inflammation may involve only a portion of the brain or become disseminated, leading to small lesions throughout it. The greater the spread of lesions, the worse the prognosis. In the case of stroke, symptoms do not progress. Patients will compensate for them and even improve over time. Tumors usually develop slowly, with symptoms gradually surfacing and progressing. By contrast in encephalitis, spontaneous brain swelling can cause uncontrollable seizures.

In identifying encephalitis, veterinarians first rule out more common disorders. If the symptoms involve seizures, they'll do a seizure disorder work-up, involving blood work and perhaps an examination of the cerebrospinal fluid that bathes the brain and spinal cord. Patients with a classic congenital seizure disorder tend to show normal chemical composition of the fluid while encephalitis patients will have elevated protein and white blood cell counts indicating inflammation.

At the laboratory, technicians analyze the fluid in molecular diagnostic tests that check for specific viral, bacterial and fungal organisms that could cause the disease. With the dog under general anesthesia, they'll image the brain with an MRI. Large lesions may be discernable with CT scan, but diffuse lesions may be missed. The MRI is the better choice because it permits advanced delineation of soft tissue. The analysis of cerebrospinal fluid, or CSF is another helpful indicator of brain inflammation. With a CSF tap costing around $250, a CT about $700 and an MRI nearing $1,200, the total expense of a diagnosis could top $2,000.

Patients with encephalitis generally require lifelong treatment with steroids or low-dose chemotherapy medication. The monthly cost for them is about $75 to S150, depending on the dog's size. n cases of bacterial and fungal encephalitis, veterinarians prescribe antibiotics or antifungals.

Inflammatory Response
Aside from viral, bacterial, fungal and parasitic causes, there is presumed to be an immune-mediated process at work in some patients — one in which the body's own immune system recognizes healthy tissue as invader cells and mounts an unfounded inflammatory response.

Fortunately, the disease is rarely passed from animal to animal, but it isn't completely known how each develops the disease. Contagious viral diseases that affect the nervous system like rabies and distemper are easily passed from dog to dog, but routine vaccinations eliminate the possibility of their infection.

Despite extensive testing, it's often never determined whether a pathogenic agent is causing the encephalitis. Many patients have been vaccinated against common pathogens that may cause encephalitis or weren't exposed to other dogs or geographical areas with infectious agents. in these cases, the cause is deemed "idiopathic," or of unknown cause.

We are testing most dogs with suspected encephalitis for infectious causes, Dr. Faissler said. "The results show that only around 10 per-cent of these cases are of infectious origin, most predominantly fungal and tick-born disease, while the other 90 percent test negative. These cases are then considered immune-mediated and are treated with steroids and/or chemotherapeutic agents to suppress the abnormal activity of the immune system on the brain tissue."

Decreasing Dosage
Steroids and occasionally other drugs are the mainstay of treatment for encephalitis. Commonly used drugs include the steroid Prednisone, the immunosuppressants Azothioprine and Cyclosporine, and Procarbazine and Cytosine Arabinoside, both chemotherapeutic agents. Long-term administration of steroids takes a toll on the body, predisposing the dog to side effects, such as liver disease, muscle wasting, ravenous appetite, weight gain, restlessness, behavioral change, excessive thirst and urination. Your veterinarian may request that blood work be performed every 3-6 months to assess liver function while treating with long-term steroids. But generally, if initial treatment is successful, the maintenance dose can he decreased over time to a relatively benign level. When the dose of Prednisone is reduced, the side effects are less severe, and the signs of the brain inflammation can be better controlled.

The benefit of the initial steroid therapy is that the medications often work miracles, creating a rapid, nearly complete recovery. Relapse is possible if the medication is discontinued. In general, most of these dogs improve if they are brought in for treatment before the disease becomes advanced," said Dr. Faissler. "In the instance that a patient suffers adverse side effects to the medication, we try to taper the dose after eight to I2 months of therapy. Many of them relapse while others do well. It is truly a case-by-case basis, so we take it slowly, one step at a time."

Because encephalitis can quickly worsen and cause irreversible brain damage, the most important advice for owners is to immediately take their dog to the veterinarian when they see the symptoms. With early treatment, affected dogs have a significant chance of recovery.

Dayna Garneau, a certified veterinary technician, is a veterinary student at Texas A&M College of Veterinary Medicine in College Station, Texas.






 

FROM: CUMMINGS SCHOOL OF VETERINARY MEDICINE AT TUFTS UNIVERSITY