Pet Medical Mystery: He ate and ate but lost more and more weight

Built like a well-muscled torpedo, Tyson was a typical boxer - all 70 pounds of him.

But last fall, he began to experience profuse diarrhea. Despite a ravenous appetite, his weight melted off. The 7-year-old's energetic wiggle gave way to a constant tremble.

"He was a big soccer player, but he didn't even want to do that anymore. He just wanted to lie around," recalled his owner, Alyssa Maule, of Levittown.

In October, she brought him to her veterinarian, who detected back pain. X-rays indicated spinal disc disease. Prednisone was prescribed for that. For the diarrhea, Tyson was switched to a bland diet.

He only lost weight faster, and produced soft, yellow stool over six times a day.

A tick panel showed elevated antibodies for Rocky Mountain Spotted Fever. Although his blood work was normal except for low cholesterol, Tyson was treated with antibiotics to be on the safe side.

But the pattern continued; by January, his ribs and hips were protruding. The vet referred him to the Center for Animal Referral and Emergency Services (CARES) in Langhorne.

CARES ran the tests again, and added more. The clinic suspected - and biopsies confirmed - a moderate case of inflammatory bowel disease, an allergic condition resulting in food intolerances. It interferes with absorption and would be a good explanation for Tyson's problems.

Treatment didn't work. By late February the dog had lost half his weight. Tyson's owners kept a T-shirt on him - both for warmth and to avoid accusations of neglect.

Although all the test results pointed to problems with intestinal absorption, the team of specialists began to wonder whether the issue involved digestion - food must be broken down into simpler substances before the body can absorb it.

Jennifer Adler, Tyson's veterinarian at the CARES clinic, had never seen such a severe case of weight and muscle loss.

"We were really worried that he was going to starve to death in front of us," she said. "So we added [digestive] enzymes out of desperation."

The enzymes break down dietary proteins, carbs and fats. Within a week, Tyson had gained more than seven pounds.

He was also switched to a low-fat, highly digestible dog food. Gradually, the diarrhea resolved.

The diagnosis: exocrine pancreatic insufficiency (EPI). The condition, also known as "maldigestion syndrome," is characterized by the inability of the pancreas to produce the enzymes necessary to whittle nutrients down to molecules small enough for the intestines to absorb them.

No matter how much animals with the condition eat, food just runs right through them. Like Tyson, they lose weight and are depleted of nutrients such as vitamins and essential fatty acids.

Exocrine pancreatic insufficiency is rare in cats as well as people. It's not uncommon in dogs, and any breed can be affected. But most canine cases are in German shepherds, typically striking when they are young.

Adler had, in fact, run a test weeks before to gauge Tyson's enzyme levels. They were normal.

But response to treatment sometimes trumps test results, which can be falsely negative. (A repeat test confirmed the diagnosis.)

What's more, the dog apparently did have the inflammatory bowel syndrome that he had been treated for earlier. It was probably caused by his digestive issues.

Now about 65 pounds, Tyson is nearing his ideal weight. His stool is normal, and he is no longer starving. He will remain on a low-fat diet, pancreatic enzyme supplementation, and vitamin B12 injections indefinitely.

Joan Capuzzi, V.M.D., is a small-animal veterinarian in the Philadelphia area. jpcapuzzi@outlook.com