Meningitis in dogs is difficult to diagnose, a challenge to treat
Isaac, a five-year-old golden retriever, has always been special. Emotionally sensitive and energetically excitable, he has had his share of mishaps. Like when a big board fell two stories and hit him on the head, knocking him unconscious. Or when he ate his Frontline
Plus flea and tick medication, which, for the uninformed, is supposed to be applied topically, not taken internally. Or when he ate a tube of antibiotic cream. Or when he ate a bottle of ibuprofen. Isaac likes to eat stuff, even food. By the age of three and a half, he was seriously overweight, topping 100 pounds. Then the seizures started.
Commonly called convulsions, or fits, seizures are the result of abnormal electrical activity in the brain. Although they can be caused by many things — including infection, poisoning, trauma, and metabolic disorders — in dogs between one and five years old, the most common cause is an inherited genetic disease called idiopathic epilepsy for which there is no definitive diagnostic test. The decision about whether to give anti-convulsant medication depends on the seizures' severity and frequency.
In Isaac's case, his episodes were rare. "Keep track of them," I advised his dad. "They may worsen over time, in which case we'll start medication, but right now I'm more concerned about his weight."
Golden retrievers are prone to obesity, sometimes due to an underactive thyroid, but Isaac's thyroid levels were fine. He just likes to eat. I can relate.
We put him on a high-fiber, low-fat, calorie-restricted, portion-controlled diet but at his next weigh-in, he had gained three more pounds. I suggested we try Slentrol®, which contains the drug dirlotapide, classified as a Gut Microsomal Triglyceride Transfer Protein Inhibitor. Just saying that should make you lose weight.
How it works to cause weight reduction is not completely understood, but it appears to do two things. It reduces fat absorption from the intestines, and it sends a message to the dog's brain that says "You're full. Stop eating."
Slentrol® is for dogs only and requires regular monitoring by a veterinarian. We started Isaac on the product. One month later, he was down a stellar five pounds. But not long after Isaac's dad called me from Florida.
"A friend is watching Isaac while I'm away," he said anxiously. "He says something's really wrong. Isaac is acting dazed and bumping into things. I told him to stop the Slentrol. I read some things on the Internet. Can you test for Cushing's disease?"
Cushing's disease? I wondered, what has that got to do with anything? Cushing's disease is an adrenal gland disorder usually caused by a benign but hormone-producing pituitary tumor. Symptoms include excessive eating, drinking, urinating and panting, thinning skin, hair loss, and pot belly.
I suggested aloud that I examine Isaac and then decide what to do. I knew his dad was just far away and feeling pretty powerless to help his buddy. Waiting for Isaac, I reviewed the Slentrol adverse side effects — vomiting, diarrhea, lethargy, anorexia, salivation, constipation, and dehydration. No mention of behavioral or neurological changes. Dogs with Cushing's should be treated before starting Slentrol, but no indication the drug could cause the disease. Although Isaac pants and overeats, he never struck me as Cushingoid.
Isaac bounded into my office, happily holding his leash in his mouth, and proceeded to bump into the door jamb. He then bounced excitedly around the exam room, tripping over the scale, knocking into the floor lamp. We got him on the table, checked his vital signs, then began evaluating his eyes. Both pupils responded appropriately to light. I darkened the room, then quickly flashed a bright light at him. At first he exhibited a slight "dazzle" reflex, i.e., he squinted. But just a little. And the second time, he didn't respond at all. I poked my finger at his eye, testing his "menace response." When someone pokes their finger at your eye, you're supposed to blink. Isaac did not react at all. He was going blind.
Grabbing my ophthalmoscope, I looked inside his eyes. I'm not an ophthalmologist, but I was able to rule out such causes of blindness as detached retinas and progressive retinal atrophy. Based on the lack of significant retinal abnormalities or other clinical signs, I suspected Sudden Acquired Retinal Degeneration Syndrome (SARDS), a disorder causing rapid and irreversible blindness in dogs. No one knows why it happens. Middle-aged to older dogs are most commonly affected. Girls more than boys. Dachshunds, miniature schnauzers, and Brittany spaniels more often than other breeds, but any dog can get it.
Oddly, dogs with SARDS sometimes show symptoms similar to Cushing's disease prior to the onset of blindness, including excessive drinking, eating, urination, and panting, lethargy, and obesity. There is no treatment.
"There are other possibilities," I told his dad. "Optic neuritis. Cortical blindness. Even a brain tumor. But I think SARDS is most likely."
Definitive diagnosis requires referral to a specialist for an electroretinogram (ERG), so Isaac's owner cut his trip short and came back to take his boy to the ophthalmologist and neurologist.
Several days later, after three ERGs, cerebral spinal fluid tap, and an MRI, Isaac was diagnosed. No SARDS. He has "immune-mediated meningitis" — inflammation of the membranes covering the brain, most marked along the pituitary area and optic chiasm, hence the blindness. Like with epilepsy, there is no definitive diagnostic test nor known cause. For some reason, Isaac's immune system was attacking his own meninges.
The Slentrol ® is in no way implicated, nor does he have Cushing's, but we have discontinued his diet for now and started Isaac on corticosteroids to suppress his immune system, and doxycycline, to rule out any possible connection to tick-borne diseases. One week after starting this regimen, he has regained his vision completely. He will stay on corticosteroids for many months as we watch for signs of relapse. He may regain the weight he lost too, but right now that is a minor concern. Besides, his dad loves him...just the way he is. Special.