Metabolic Bone Disease in Iguanas
Metabolic bone disease (MBD) is most commonly seen in young, rapidly growing reptiles and amphibians and it is one of the most common reason iguanas are presented for veterinary care. MBD results when an imbalance in the ratio of calcium to phosphorus in the blood results in absorption of calcium from the exhisting bone thus weakening the bone. This imbalance may result from calcium deficiency, phosphorus overload, and/or inadequate vitamin D3. Many iguanas are fed diets that consist of only lettuce, broccoli, and a few other vegetables. These diets are deficient in calcium and very high in phosphorus. A desired ratio is 2:1 i.e. 2 parts calcium to 1 part phosphorus. Many mineral supplements contain adequate calcium but also contain equal or excessive amounts of phosphorous thus defeating the purpose of feeding a supplement. Vitamin D3 is necessary for the Iguana to absorb and use calcium from food sources. Iguanas require exposure to a very specific wave length of light in order for them to make vitamin D3 . This light can be provided through exposure to direct, unfiltered sunlight or by use of very special artificial light sources that provide broad spectrum light such as a Vita-Lite or Rep-ti-lite. If this light passes through glass, plastic or Plexiglas then the beneficial wavelengths will be filtered out and rendered useless. Please refer to Green Iguana Care, by Steven D. Garner, DVM, DABVP Diplomate, for further information on feeding, diet, and lighting suggestions.
In juvenile reptiles, most symptoms are related to the skeletal system such as fibrous osteodystrophy (FO) and fractures. The earliest and most consistent sign is partial to complete lack of truncal lifting i.e. a normal iguana lifts its trunk or chest and proximal tail up off the ground while walking or disturbed. Early on in MBD , the iguana may drag its pelvis and tail but is still able to lift its chest. As the metabolic bone disease progresses, the lizard drags its entire chest while walking. In advanced stages of MBD, the lizard can no longer lift its body, the legs move vigorously yet the lizard is unable to walk. Another common finding is a soft or pliable lower (mandible) and/or upper (maxilla) jaw. This is best evaluated with the mouth held open. To do this, gently restrain the upper jaw and pull down on the dewlap with the other hand. Once the mouth is open apply gentle pressure to the tip of the jaw pushing it backward towards the neck with an index finger. The jaw should feel hard like bone and should not give or deform. With MBD, the jaw will feel soft and collapse or deform inward. As MBD progresses, traction of the muscles of the jaw result in the tip of the jaw being pulled inward and the lateral portion of the jaw bowing outward causing the appearance of an underbite. Single and multiple fractures of the long bones of the legs are common in reptiles with MBD. Lizards may show lameness or reluctance to move. The fractures may occur simply from the bending forces exerted on the bones by the muscles of the leg as they contract during normal movement. Fibrous osteodystrophy (FO) generally affects the long bones or the bones of the jaw. Superficially, the legs look well fleshed and muscular (popeye legs) however when felt, the legs have a firm feel-more like bone. This is due to the presence of excessive fibrous tissue deposited by the body along the long bones in an attempt to provide strength and support. Lizards with MBD have a gradual decline in appetite and weight loss. If the jaw bones are affected, the lizard may want to eat but can not, thus with out intervention and treatment, it will slowly starve to death.
In adult reptiles, symptoms such as paresis (weakness to paralysis), muscle tremors and seizures are common clinical signs of MBD. In addition to diet and lighting deficiencies causes of MBD in adult iguanas include kidney disease and egg production in females. In all cases, by the time clinical symptoms become evident, the disease has progressed to a critical stage and requires immediate, long term treatment and permanent correction of the diet and husbandry practices that initially led to the problem.
Diagnosis of MBD is made based on the physical examination and history of the diet and care of the reptile. Individual cases may require additional diagnostic evaluation such as blood work, fecal (stool) examination and radiographs. Fractures will require stabilization. Depending on the individual case, stabilization may be provided with splints, bandage or surgical placement of pins in the bones.
In general, all cases require some level of the following treatment.
- Handle carefully!! Handle only when necessary to feed or medicate. Excessive struggling when handled can cause fragile bones to break!!!
- Conversion to proper diet. If not eating, tube or hand feeding will be necessary. Tube feed _____________ ml orally _____________times a day.
- Provide broad spectrum light source. Light exposure 10-12 hours per day with light positioned no more than 18” above the reptile. Do not allow light to pass through glass, plastic or Plexiglas. Replace bulbs every 9-12 months to insure maximum performance.
- Warm environment to 85-90 degrees to aid metabolism and digestion.
- Vitamin D3 injection given initially. Repeat in 7 days.
- Initially an injection of calcium may be given. This may need to be repeated in 7 days
- Oral calcium supplementation. Neocalglucon- Give _______ml orally twice a day for a minimum of 90 days. Treatment is required until all clinical signs have resolved. Medications can be refilled as needed.
- Please schedule an appointment for a recheck examination in _____________ days. This recheck will be at no additional charge. If during that examination new problems are discovered, additional tests/treatment may be required. This would be at an additional fee.
- Please call Safari Animal Care Centers (281-332-5612) if you have any questions, are unable to give the medications as directed or ____________________’s condition seems to worsen.