Iguana Bone Disease (NSHP, MBD)

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The most common reptile brought to our hospital is the green iguana. The primary reason owners bring in their ill green iguana’s is because they have developed a disease called metabolic bone disease (MBD), also known as nutritional secondary hyperparathyroidism (NSHP). The cause of this disease is poor husbandry, especially an inadequate diet. Unfortunately, the literature abounds with erroneous information on the precise needs of these creatures. This outdated an incorrect information continues to be propagated by individuals and organizations with good intentions but limited knowledge.

Iguanas are not the only reptile that encounters this problem. We find it in many types of lizards, turtles, and tortoises. It does not occur in carnivorous reptiles like snakes and monitor lizards very often because the whole prey they consume provides a proper diet.

We have a short Quicktime movie on an Iguana with twitching muscles. You need Quicktime from www.apple.com to view it.


Cause

This disease has many factors that work together in causing this condition. The primary reason iguanas develop this disease is due to a diet too low in calcium. More specifically, the ratio of calcium to phosphorous (usually the phosphorous is too high) in their diets is inadequate to promote growth and sustain normal physiological functions. As a result, they become very ill, and can even succumb to the disease.

Other factors that exacerbate the poor diet problem are common in most households that have iguanas. Inadequate exposure to direct sunlight (not through glass), not keeping the humidity at 90% and not keeping the temperature at 90 degrees F all add to the problem:

    • Sunlight of a specific ultraviolet frequency is needed to produce vitamin D3 by the iguana’s skin. This vitamin is needed for the absorption and utilization of calcium in the diet. No matter how much calcium there is in the diet, without this vitamin the calcium would not be be absorbed or utilized . This is why milk that we drink is fortified with vitamin D. Black Lights and other artificial ultraviolet lights are helpful, but they can not replace sunshine.
    • In order to maintain normal bodily functions (ability to digest food, fight infections, etc.) an iguana needs to maintain a high body temperature. Since they are reptiles, they maintain this temperature by absorbing the heat from their environment. They can not produce enough internal body heat like birds and mammals can when placed in a cold environment. also, the precursor to vitamin D needs to be at the proper temperature to be converted to the active form of the vitamin.

In the semi arid environment in some parts of the country, or the heat needed to warm homes in the winter, many iguanas live in a perpetual state of dehydration. This dramatically interferes with their physiology and predisposes them to many problems.

This is a typical Iguana cage that is inadequate. There is no branch with leaves to bask on, no access to any sun, let alone through the glass, and inadequate humidity. The bowl of water does not give enough moisture, and the heat lamp that is present in the corner does not supply proper ambient heat. Putting dirt in the bottom of the cage is a good idea.

Symptoms

Iguanas with this disease have many problems. The bones might be swollen, soft, or even fractured. In severe cases the blood calcium level becomes so low that tremors occur. The jaw might be swollen (called lumpy jaw by some people) because nature is trying to bring in supporting tissue to make up for the lack of strength to the bones of the jaw. The same thing happens to the bones of the legs, and when the problem is severe enough, or has gone on long enough, the bones of the arms and legs can fracture (called a pathologic fracture) all by themselves.

Some of these iguanas will be unable to walk properly due to spinal cord damage, and many of them will be more susceptible to common infections because they are too weak to develop a proper immune response. As the bones of the jaw become weaker it becomes impossible to eat, further exacerbating the problem.

They might have distended abdomens and bones leading their owners to the erroneous conclusion that their pet is fat and sassy, and receiving an adequate diet. Growing iguanas and females laying eggs have a greater need for calcium and might be more prone to this problem. Females with eggs might not have the strength to lay them, and sometimes even require surgery if they become egg bound.

Lumpy jaw occurs when the body brings fibrous tissue to the area to stabilize the weak bones. A lump at the jaw can also be caused by an abscess.

The fold of skin on the side of this iguana is evidence of dehydration.

This Iguana has such a low calcium level that the muscles are twitching. This is called tetany, and is a serious sign. The two most common causes of tetany in an Iguana are MBD and Kidney failure.

This Iggie is so weak it cannot move properly

 

Diagnosis

A diagnosis of NSHP is made based on history, physical exam findings, and radiography. The history might indicate a diet of iceberg lettuce, dog or cat food, or packaged iguana meal. Swelling of the jaw and legs, low body weight, weakness, dehydration, poor appetite, and lethargy all might be noted on physical exam. X-rays are very diagnostic. Even though this is a problem of low calcium level, blood samples show normal calcium levels commonly.

This is the femur (thigh) bone of a healthy iguana. Compare it to the diseased one below.

This is the thinning (arrow) that occurs in this disease. In addition to poor bone strength, this iguana has an infection.

This iguana has a severe form of the disease. The spine is deformed which has interfered with the nervous system, so it is unable to walk or eat well. This creature is gravely ill. To let a creature deteriorate to this point is a crime.

An x-ray reveals the extent of the curvature problem to the spine.

Treatment

Iguanas that are diagnosed with NSHP are usually very ill and often need to be hospitalized. During hospitalization they are given fluids to correct dehydration, a special liquid diet, injections of vitamin D3, injections of calcium, oral calcium, and antibiotics if they have an infection. Those that have pathologic fractures are splinted.

After they are stabilized in the hospital they are sent home with calcium supplements, antibiotics if needed, and their dietary deficiency is corrected. They need to return weekly for at least several weeks for vitamin D3 injections and calcitonin injections.

A typical splint applied when both rear legs have pathological fractures.

An x-ray of this splint shows the padded paper clips that are used for support.

This different case was referred to us. The splints on these front legs are inadequate, as evidenced by the displacement of the fractured ends.

We performed surgery in order to correct this problem. These pins will be removed in 1-2 months.

 

This disease occurs in other lizards, like this young chameleon with numerous pathological fractures. There are differences in why this species gets this problem as opposed to the green iguana, but the main problem of inadequate husbandry stays consistent.

This little guy has fractures on all 4 legs due to inadequate husbandry.

In some cases the bones that allow the tongue to move normally are permanently injured and the tongue is rendered useless.

This disease also occurs in tortoises.The shell is soft due to inadequate nutrition.

Prevention

It must be fully understood that iguanas are ectothermic animals. This means they are highly dependent on their environment for their normal physiological functions, much more so than birds and mammals. They come from Central america where the temperature and humidity are consistent- 90% humidity and 90 degrees F. In addition, they bask in the direct sun many hours each day. If these conditions can not be replicated then these animals should not be kept in captivity. Ignorance of their needs is no excuse.

Their diet should consist heavily of dark green leafy vegetables in order to have the proper ratio of calcium to phosphorous. Contrary to what you may read elsewhere, these animals are not omnivores, they are strictly vegetarians, even when they are young. Therefore, high protein diets (dog food, cat food, protein supplements) are not to be fed to them. These high protein diets will cause them to grow bigger and faster, but will also cause their kidneys to fail. Vitamin supplements that contain calcium should be given weekly.

The following list describes would should and should not be fed. A combination of several items from the “Should Be Fed List” need to be fed, not just one or two items. For small iguana’s it is helpful to dice up your vegetables into very small pieces so that they don’t eat only a few items.

Foods That Should Be FedCollared GreensMustard GreensGreen LeafRed LeafButter leafDandelion GreensMango and PapayaBroccoliNon toxic flowers Foods That Should Not Be FedDog FoodCat FoodRodentsEggsIceberg LettucePizzaMeatInsects

Prognosis

This disease is correctable and preventable. If a pet iguana is brought to us in an advanced state of the disease then the prognosis is not good. Otherwise, we are able to return a large percent of them to relative normalcy if our full treatment regimen is followed. After the immediate problem is corrected it is mandatory to provide the optimum environment for their proper quality of life.