What's causing dog's tremors?

Auggie, a 11/2-year-old male Jack Russell terrier, presented to our clinic with muscle tremors. The owners first noticed the tremors the previous evening, when the dog appeared to have tripped on the stairs.

Fine muscle tremors, primarily in the buttocks, were apparent on physical exam. The neutered dog showed no pain upon palpation of his spine and manipulation of his neck and limbs but seemed somewhat stiff. He was well hydrated and pulse was normal.

"This is the calmest Jack Russell I've ever seen," I said several times, perhaps ominously.

In a dog, tremors can indicate many things, including fear, pain, or exposure to toxins.

I recommended bloodwork to help categorize the tremors, but Auggie's owners declined due to cost ($115). With a generally unremarkable exam and no bloodwork, I reluctantly defaulted to the possibility that his tremors were associated with pain, perhaps from a sprain caused by his stairway fall.

He went home on a non-steroidal anti-inflammatory medication with instructions to bring him back if tremors persisted past a day or two, or if new problems arose.

His conscientious owners brought him back two days later. Not only was Auggie still shaking, he also had stopped eating.

He appeared weak, and his tremors had worsened slightly. His skin had lost its elasticity, indicating dehydration. His body temperature, 99.2 degrees, was low for an adult dog, and his heart rate had slowed. Normally, heartbeat depends on body size: The smaller the dog, the faster the beat. Auggie, at 18 pounds, had a rate that resembled a Labrador retriever's.

There were several possible explanations, most notably shaker syndrome. It is a neurologic disease that afflicts primarily dogs with white coats but that can occur in canines of other colors. With his widely dispersed body tremors, Auggie looked like a shaker dog. The condition is treated with corticosteroids (prednisone) to reduce nerve inflammation. His slow heart rate and low temperature, however, didn't completely fit the diagnosis.

The owners wanted to pursue prednisone, but first some other possibilities had to be ruled out. They declined a full blood panel, but agreed to one quick, inexpensive - and perhaps significant - test: blood glucose ($20).

If the dog's blood sugar level were high, indicating possible diabetes, corticosteroids could cause harm.

Likewise, low blood sugar could indicate diseased adrenal glands - and corticosteroid therapy would interfere with confirmatory testing for adrenal disease.

The dog's blood glucose came back very low. Though that might have been explained by his recent lack of food or incessant muscle tremors, it also fit the clinical picture of adrenal disease. Luckily, there was a $45 blood test that could rule it out: electrolytes.

The electrolyte panel showed elevated potassium and decreased sodium that were consistent with Addison's disease, caused by underactive adrenal glands, although not sufficient for diagnosis.

Auggie was stabilized with intravenous fluids for rehydration and electrolytes, plus a shot of dexamethasone to improve his circulation. The final bloodwork - an ACTH stimulation test - was positive for Addison's.

Situated at the pole of each kidney, the two tiny adrenals churn out more than 30 hormones that control heart activity, blood pressure, blood flow, energy storage, immune function, sex hormone secretion, and more.

Human adrenal insufficiency (hypoadrenocorticism) was first recognized by the English physician Thomas Addison in the mid-1800s. The first canine case was reported in 1953. The breeds most affected are the standard poodle, West Highland white terrier, wheaten terrier, Portuguese water dog, Rottweiler, great Dane, and Basset hound. It is most often seen in young to middle-aged dogs, more commonly females.

The most famous purported human case was President John F. Kennedy. But Addison's is quite rare in humans and canines - two or three dogs out of 10,000, though it may be underdiagnosed due to its subterfuge.

Known as the "Great Pretender," it typically causes nonspecific problems like lethargy, weakness, dehydration, weight loss, excessive urination, vomiting and diarrhea, signs that can mimic gastrointestinal illness, heart disease, infection . . . almost anything, in fact.

Auggie had already been experiencing weakness, tremors, slowed heart rate, and dehydration. But due to the vigilance of his owners, who noticed early problems, he was diagnosed before going into "Addisonian crisis," an often-irreversible situation.

Soon after treatment, Auggie was eating and full of energy. His tremors disappeared. He will get lifelong monthly injections of Percorten-V, a synthetic corticosteroid, plus daily low-dose prednisone, regular bloodwork, and instructions to avoid stressful situations, which could aggravate his condition.

Three months later, his prognosis is for a full and healthy life.