I have a confession to make, actually two.

First off, I am way behind on addressing letters. Second, I do not necessarily respond in order received. I try, but if there is a letter describing a situation that is more critical, I will move it to the top of the pile.

Today's patient would represent one of these situations.

Scud is a 2-year-old male bearded dragon, a species of lizard found wild in Australia. These guys are popular for those seeking a hardy, friendly pet.

Scud, however, is having a problem. He is shaking when he moves, said Dana. She said the shaking seems to be getting worse. Initially, it was quite subtle, but lately, Scud seems to shake with every motion. His ability to get around has decreased, but Dana says he is eating his crickets and occasionally various green leafed vegetables.

There are multiple possible causes for Scud's shaking, but a likely one is nutritional secondary hyperparathyroidism. Now that's a mouthful.

Nutritional secondary hyperparathyroidism is a disease that occurs as a result of a poor calcium balance in the diet. More correctly, it is an issue with the calcium-to-phosphorous ratio. This disease can occur in virtually all vertebrate animals, including humans. If left unaddressed, it results in death.

The pathophysiology of this disease - its mechanism of action, if you will - involves the interaction between the calcium taken in through diet and the parathyroid gland, which is primarily responsible for calcium balance in the body. Parathyroid hormone is secreted by this gland in response to lowering calcium levels in the blood. The response within the body is to absorb more calcium from the gastrointestinal tract, i.e. the food eaten. In cases of longer-term low-calcium levels in the blood, usually because of improper diet, calcium is robbed from the bone. It is this cascade of events that is likely responsible for Scud's tremors.

Calcium is necessary for normal muscle function, but in Scud's case, the blood level of calcium is too low and his muscles are not able to function properly, thus leading to the symptom of tremors.

These lizards usually start with tiny little tremors within muscles and then progress to uncoordinated limb and body motion. In severe cases, these animals cannot effectively move or even raise their bodies.

There are cases when the tremors can come on very acutely if the calcium level drops rapidly before the parathyroid response can occur. This is more common in older lizards.

What is happening to Scud is that his calcium intake has been too low for a while, leading to the body's response discussed above. Because of the calcium release from his bones, his skeleton is actually dissolving. This is a survival mechanism, primarily because the body cannot function without calcium and, at least initially, this makes the bone expendable. In severe cases, I have seen these patients with virtually no bone density on radiographs. Surprisingly, although logically, their blood calcium levels can be normal owing to the calcium being liberated from the bone, at least until there is no more bone to dissolve.

Scud's calcium levels are low; otherwise, he would not be showing the tremors.

Treatment for this disease is multifaceted, depending on the severity of the patient's calcium problem. If the process is caught at an early stage, before the body has responded by significantly cannibalizing its bone, calcium supplementation in the diet can bring about resolution. In patients with severe bone loss, we not only have to supplement the calcium in the diet but we must also attempt to reverse the bone-dissolving mechanisms that have been activated as a result of improper diet. This requires special injectable medications and, depending on the severity of the lizard's condition, it simply may not be possible to cure.

There are other factors that are involved in calcium metabolism, including exposure to ultraviolet wavelengths of light that affect calcium absorption from the diet. However, that discussion is for another time. Right now, Scud needs veterinary medical attention and hopefully it is not too late for something to be done.

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(Jeff Kahler is a veterinarian in Modesto. Questions can be submitted to Your Pet in care of LifeStyles, The Modesto Bee, P.O. Box 5256, Modesto, CA 95352.)