The Description - Metabolic Bone Disease, or MBD, is the collective name given to a number of symptoms and problems commonly seen in captive iguanas. Other names for MBD include Fibrous Osteodystrophy and Secondary Nutritional Hyperparathyroidism. The bad news is that MBD is the most common ailment seen in pet iguanas. In fact, most reptile vets would agree that it is way too common. The good news is that it is easily preventable with proper care and is treatable if it is spotted early enough. The Causes - MBD can be caused by a variety of factors or a combination of factors, most of which are related to improper husbandry. MBD is ultimately a calcium deficiency. It can be thought of as the iguana equivalent of rickets. Some cases of MBD are caused by hormone imbalances brought on by other diseases. Most often, however, MBD is caused by one of the following factors: not enough calcium in the diet, lack of exposure to UVB light, and inadequate temperatures. Calcium is a very important nutrient. In addition to other things, calcium is used to build bones, and it plays an important role in nerve functioning. In a healthy animal, calcium is in balance in the body. It interacts with other nutrients, such as vitamin D3 and phosphorus, and is regulated by various hormones. Too much or too little of the calcium, the other nutrients it interacts with or the hormones that regulate it will cause the delicate calcium balance in the body to be thrown off-kilter. One of the causes of MBD in iguanas is a lack of calcium in the diet. As explained in our Foods and Feeding section, iguanas should be given a diet that contains twice as much calcium as it does phosphorus. If the diet lacks calcium, the body will attempt to get it from some other source, and that means pulling it from the bones. MBD will result. UVB light also plays a very large role in MBD prevention. Upon exposure to UVB, an iguana’s skin will manufacture vitamin D3. This vitamin plays an important part in regulating how the body absorbs and uses calcium. Without exposure to UVB light, either through artificial UV bulbs or, better yet, unfiltered sunlight, iguanas cannot manufacture vitamin D3. Without vitamin D3, their bodies cannot properly absorb and use calcium from the diet. Since there is little evidence at this time that iguanas can efficiently use vitamin D3 received from their food, the best way to provide your pet with it is by making sure it gets adequate exposure to UVB. This, along with providing a calcium-rich diet, is one of the most important preventative measures you can take to avoid MBD in your iguana. Lastly, making sure you keep your iguana at the right temperature is another way to avoid MBD. Since they are cold-blooded reptiles, iguanas rely on their surroundings to provide them with the heat necessary to properly digest their food. Iguanas that are kept too cool will be unable to digest their food well, and will not adequately absorb the nutrients, including the calcium, available. This can also contribute to MBD. To learn more about proper temperatures, visit our Habitat page. There is another reason why an iguana may develop MBD - breeding season. This is really only a problem for females. As breeding season progresses, female iguanas develop eggs in their ovaries, even if they have not mated. As the egg shells develop, large amounts of calcium are needed. During this time, females are highly susceptible to MBD. Owners of females should be especially wary during this time of year, and should keep a close eye out for MBD symptoms. Extra calcium should be provided during this time. For more information on breeding season, see our Breeding Season Issues page. The Symptoms - MBD may manifest itself in many ways. Most often, the first symptom to appear is thin, easily broken bones. Many owners do not realize that their iguana has MBD until it breaks a bone doing something that a healthy iguana would have no trouble with, such as climbing or jumping. As bones weaken, the body will attempt to strengthen them by laying down fibrous connective tissue at the points of strain. This will often result in swollen, “popeye” legs. The legs may feel bumpy to the touch. They may become bowed as the weak bones bend under the pressure of the muscles pulling on them. Breaks may result in twisted and crooked backs, toes and limbs. Spinal cord injuries from such breaks may result in permanent paralysis. This badly twisted arm belongs to Devo, a female green iguana who suffered through a bad case of MBD with her previous owner. Notice that her foot does not lay flat, making it difficult to climb and walk. This is Quasi, a female iguana whose obviously twisted spine is the result of past battle with MBD.

Another common symptom of MBD is a soft or spongy lower jaw bone. Like the limbs, the jawbone may swell as connective tissue is laid down to replace lost bone. Eating may become difficult or painful, resulting in lost appetite. In severe cases, the bottom jaw may recede from the top or grow at a slower rate, resulting in an overbite which contributes more to eating difficulties. The overbite may also lead to gum abrasions and other related problems. This is Devo again. Notice her small size. Stunting is another symptom of MBD. Devo was four years old when this photo was taken, yet she is barely bigger than her adoptive owner's hand. Also notice her receded lower jaw, twisted arm and hunched back. If MBD affects the nerves, trembling or weakness in the limbs may occur. In worst cases, partial paralysis may result. Often this is evident in the back legs and tail. The iguana may drag itself along with its front legs. It will be unable to climb or get around properly. Any of these symptoms will produce an iguana that doesn’t feel well. Iguanas suffering from MBD will often show general signs of illness, such as lethargy, weakness and lack of appetite. If you see any of these symptoms, your iguana may have MBD and should be seen by a qualified reptile vet immediately. If left unattended, MBD can permanently maim or kill your iguana. DON’T RISK IT! The Treatment - Thankfully, MBD can be reversed if it is treated early enough. There are many courses of action that may be taken to treat MBD, depending upon the severity and particulars of the case. Broken bones will be set and allowed to mend. Extra calcium and exposure to UVB light will be given. Any other necessary changes in husbandry will be recommended. Physical therapy may be applied to weakened muscles and paralyzed limbs. Many of the symptoms can be reversed. Trembling, weakness and partial paralysis will often go away once treatment is begun. Bones will become strong again, and appetite will return. Some things, however, will be there forever, even long after the iguana has recovered from MBD. Distorted jaws, toes, backs and limbs will remain. Normal movement and climbing activities may still be restricted. Pain may continue. Females may be unable to lay eggs due to twisted spines. Devo eventually became healthy enough to develop eggs, but was unable to lay them due to her twisted spine. As a result, she had to undergo an emergency spay. Problems with defecation may occur for the same reason. And, of course, any spinal cord injuries obtained from broken backs will result in permanent paralysis. Conclusion - Many iguanas have recovered from MBD and lived fulfilling lives, despite permanent physical deformities. But why put your iguana through such a terrible experience when MBD is so easily preventable? It is extremely telling that wild iguanas do not suffer from MBD. This disease is completely the result of improper care in captivity. You are your iguana’s caretaker. It relies on you for everything it needs. Do not let it down, for it will surely suffer for it.

Tricia Power's page, Metabolic Bone Disease, is short and sweet but loaded with more detailed information.

For a more technical and detailed discussion of MBD, visit Melissa Kaplan’s MBD pages: Identification and Treatment of MBD and Calcium Metabolism and MBD.