Jennie Cardin just needed to get her groceries inside.

But when she opened the front door of her Kensington home, she was swept aside by her American foxhound, Troy, who ran off June 7 into the woods at the end of the street.

Jennie chased Troy past 10 houses, but he outran her.

“He was just gone,” she said. “He just evaporated.”

Jennie and her husband, Tom, spent five days searching for Troy. Tom drove around the neighborhood listening for Troy, who often barks loudly because of his disorder. Jennie visited and contacted animal shelters.

They were especially worried because Troy has received a diagnosis for anxiety, for which he takes medication; they feared that if people picked him up, they wouldn’t be equipped to handle his needs.

“I was just on high alert because Troy was on medication,” Jennie said.

Luckily, after passing out fliers and e-mailing, contacting animal shelters throughout the Washington area, Jennie received a call June 11 from an Albert Einstein High School employee and a student from the school.

They’d found Troy. He was safe; he’d been living in the student’s backyard for several days.

The Cardins’ search for Troy highlights the problems that owners of pets with special needs face. The owners of such animals often must make environmental and lifestyle adjustments to accommodate their pets, said Carlo Siracusa, a lecturer in animal behavior at the University of Pennsylvania.

Veterinary behavioral medicine developed in the 1980s — so recently that doctors haven’t come to a consensus on a definition of animal anxiety. No exact data exists on how many pets receive a diagnosis of the disorder, Siracusa said.

But Nicholas Dodman, director of the animal behavior clinic at Tufts Cummings School of Veterinary Medicine in Medford, Mass., estimated that 35 percent of the 80 million dogs in the country suffer from anxiety. He thinks the number of cases has increased in recent years, which he attributes to bad breeding.

“Breeders don’t understand how to make use of the critical period of learning,” Dodman said. Dogs in many puppy mills are given little to no socialization during their first few months, so many develop anxiety disorders when they’re surrounded by people and other animals later on.

Troy has been prescribed Prozac and Benadryl for his anxiety. He often gets hyperexcited, panting and barking excessively, Jennie said. He also struggles with learning.

The couple has owned Troy for a year, and just succeeded in teaching him to fetch a ball.

“He used to just stand there and bark at it,” Tom said.

The Cardins adopted Troy last May. They have also owned another dog, a Jack Russell terrier, for 12 years. When they began to be concerned by Troy’s barking, they took him to animal behaviorist Kathryn Meyer at the Veterinary Behavior Clinic in Gaithersburg.

“Troy was one of only two dogs in my 12 years in the practice that I’ve had to medicate during the appointment,” Meyer said. “He was barking incessantly. He’s a little out of the ordinary.”

Pet behavioral problems are getting increased attention, said Heather Bialy, director of Shelter Services for the Humane Society of the United States.

“Owners are starting to realize that what they thought were little quirks in their pets are actually problems,” she said.

She attributed the problems to dogs’ relative inactivity. Dogs used to be working members of a family — herding and guarding other animals — and were mentally exhausted at the end of the day, with little time to develop behavioral problems. Now, many owners don’t have the time or resources to keep their pets’ environments mentally stimulating.

Allison Seward, a University of Pennsylvania behavior clinic veterinary assistant, said she thinks the opposite is true — with more dogs living in urban areas and near other pets, they face more social pressures, she said.

“We used to just take dogs on walks,” Seward said. “Now, we want to take them to the dog park, and we want them to be friendly to the neighbors . . . and we don’t want them to bark at the Malteses next door. We’re making a lot of demands.”

Genetics can also be a factor in anxiety, Siracusa said.

He recommends helping animals avoid the stimulus that upsets them, in addition to changing their environment to include a quiet place where they feel safe. Medication should be a last resort, he said.

Dodman recommended desensitizing pets to the stimulus they fear — in other words, exposing them to the stimulus little by little until it is no longer a source of anxiety.

The Washington Humane Society tries to accommodate stray animals with anxiety, said Chief Operating Officer Stephanie Shain. During the five days in which District shelters are required to hold pets, the shelters place animals with behavioral problems in quieter parts of their kennels.

Troy settled back in without incident at home after being reunited with his owners. Despite the Cardins’ fears, Jennie found Troy sitting in the Einstein student’s back yard, only a mile away from home. She gave the student a $100 reward.

“The fliers worked,” she said. “I’m elated.”