The Must Knows of Metabolic Bone Disease (MBD)
By Eric Roscoe
Perhaps one of the most common and widely reported, but also one of the most preventable disorders seen in captive and pet reptiles of many species is that of Metabolic Bone Disease, or MBD, or also sometimes known as rickets. MBD is somewhat of a collective name given to a wide variety of signs and symptoms that gradually and systematically weaken the affected animal’s bones, metabolic, and other bodily functions. The fancier, more technical or medical terminology for this condition can also include Fibrous Oseteodystrophy, Secondary Nutritional and/or Hyperparathyroidism, Osteomalacia, or Osteoporosis. In this educational article, the causes of MBD will be highlighted upon, as well as the signs and symptoms, diagnosis and prognosis, care and treatment options, and ultimately, preventative measures which can be taken.
Unfortunately, MBD is most commonly seen in those reptile species which require ultraviolet light (or UV) such as sunlight, and the supplementation thereof for the proper or complete synthesis and production of calcium, phosphorus, vitamin D3, and other vital nutrients. It is perhaps most and extremely commonly seen in green iguanas (Iguana iguana), bearded dragons (Pogona vitticeps), and Chinese water dragons (Physignathus cocincinus), but can also affect nearly all other lizards, amphibians, as well as turtles and tortoises through pyramiding, or the softening and weakening of their shells, which will also be discussed in this article. MBD is usually much more rarely seen in snakes, which are generally less dependent upon supplemental UV lighting for vitamin D3 synthesis, and are fed whole food items that provide a greater calcium to phosphorus balance, but this condition can affect them as well if perhaps their diets, or other husbandry and environmental conditions are extremely poor.
What Causes MBD?
Metabolic bone disease can be the result of a variety of different factors, or combinations of factors thereof, the majority of which are caused by improper diets, husbandry, and/or nutrition. Too little, or in some cases, too high of calcium is perhaps among the leading causes of MBD in captive reptiles. Calcium is an essential nutrient in promoting bone growth and development, and also supports proper nerve functioning as well. In most healthy animals, and animals in the wild, there is typically a balanced calcium-phosphorus-vitamin D3 ratio that is regulated and maintained by various bodily hormones. Subsequently, if there is too much or too little calcium in an animal’s diet, these balances will be disrupted. As with other adverse physiological effects, such as starvation (where fat and muscle mass begin to be expended once other sources of nutrition have been exhausted), once an animal’s normal calcium deposits or reserves are expended, other sources, such as the animal’s bone material will be used to derive their needed levels of calcium, thereby resulting in MBD.
UVB lighting and heating also plays a major role in MBD prevention. Many reptile and amphibian species require access or exposure to artificial UVB and UVA, or even better yet, natural and unfiltered sunlight whether they are in captivity or the wild. Many herptile species require this supplemental UVB lighting in order to properly manufacture and maintain adequate ratios of calcium-phosphorus-vitamin D3, and without this component, are unable to properly absorb or utilize calcium or these other nutrients. Very often, improper or insufficient UV-A and UV-B lighting and heating, or no UV at all, are among the leading causes of MBD in captive animals. Furthermore, inadequate, or too high or low of temperatures provided will also often contribute to the slowing and/or impairment of these animal’s digestion, metabolic functions, and calcium and vitamin D3 intake.
Occasionally, MBD may also be caused by factors other than calcium, UV lighting and heating, and inadequate temperatures. Other diseases and disorders that can have adverse affects on a reptile or amphibian’s organ systems, including their livers, kidneys, parathyroid glands, or small intestines that affect the animal’s metabolism and calcium/vitamin D3 intake can also result in MBD as a secondary condition. An animal’s reproductive status, such as in the case of breeding or ovulating female animals, can be another contributing factor to MBD. During their breeding seasons, eggs develop in females within their ovaries, which act as another major draw requiring additional calcium intake. As such, gravid or ovulating females can also become very susceptible to MBD as well, and should be closely monitored for signs and symptoms and provided with additional supplementation. Even all of these other causes of MBD, however, are also still related to the intake of calcium and/or vitamin D3 nutrients.
What are the Signs and Symptoms of MBD?
Metabolic bone disease can manifest itself in a variety of different ways and locations, and is almost always a slow, gradual process. It does not happen suddenly, and very early signs, symptoms, and stages can often be missed or overlooked, particularly by novice pet owners and reptile keepers. MBD can affect an animal’s head, jaws, limbs, spinal column, body, toes and digits, and/or tails. As their bones become brittle and weakened due to the leaching of calcium from them, the animal’s body will attempt to strengthen and repair them by synthesizing and laying down new fibrous connective tissue to the points of strain. This often results in the swelling or bowing of limbs or other affected areas, and bones and ligaments may break due to added pressure from their muscles pulling on them. Below is a list of many of the signs and symptoms to watch for associated with MBD:
-Thin, brittle, or easily broken bones without external injury.
-Swollen, twisted, crooked, and/or bowed limbs, joints, toes and digits, spinal columns, tails, or other areas of the body. Lumps or hard bumps along the limbs or spinal column as well.
-Soft, spongy, mal-aligned, or disfigured mouth and jaws with an underbite or overbite.
-Anorexia, such as refusal to eat, painful, or difficult ability to eat or feed properly.
-Stunting and poor overall growth and development.
-Evident lameness such as poor, uncoordinated, or non-usage of limbs, toes and digits, and/or tails. Difficulty walking, moving, climbing, jumping, lifting of the body, or other normal motor functions.
-Soft, spongy areas anywhere on the shells (carapace, bridge, and/or plastrons) of turtles and tortoises.
-“Pyramiding” in turtles and tortoises, where excess calcification, or too little calcium results in disfigured, distorted, and asymmetrical shells. Excess sculpturing or “pyramiding” of the carapace and carapace scutes beyond what is normally seen according to the species.
-Trembling, seizures, weakness, paralysis, and other neurological signs and symptoms if the nerves are also affected.
-Other general signs of illness including, but not limited to weakness, weight loss, constipation and impactions, lethargy, anorexia/lack of appetite, etc.
Treatment and Prognosis
Metabolic bone disease can often be diagnosed by your veterinarian based on the findings of a physical and/or visual examination, as well as the dietary and husbandry history of the animal in question. Radiographs, or more commonly known as X-Rays, as well as conducting bloodwork can also help confirm and determine the extent and severity of the MBD, whether there are any fractures, and guiding the process for treatment going forward.
There are many different treatments and courses of action that can be taken depending on the severity, extent, and other particulars of each case. Fortunately, if detected early enough, MBD can often be corrected and reversed through making changes and improvements to the husbandry of the animal by providing the needed or adequate levels of UV-A and UV-B lighting and heating, proper supplementation, and other nutrients. Many of the other signs and symptoms of MBD can or will cease once a proper course of action is taken as well. Providing adequate space for exercise and physical therapy can also often help re-develop weakened bones and muscles as well.
In more severe, advanced, or progressed cases, however, the damage caused by MBD will more than likely be permanent and irreversible, but further advancement can be slowed or stopped through appropriate corrective action. In these cases, your veterinarian may prescribe oral or injectable calcium supplementation such as calcium glubionate (or NeoCalglucon), calcium lactate (Calphosan), or calcium gluconate. Calcitonin may also be prescribed as a further preventative measure as well. Any fractures or broken bones can also be set, and allowed to heal and mend over time as well.
Overall, without treatment or intervention, MBD typically advances and becomes progressively worse over time. Ultimately, MBD is usually fatal for your reptile or amphibian if action is not taken, as their bones, organs and organ systems continue to be affected further to the point of ceasing function. Fortunately however, with prompt treatment and action, the prognosis for MBD is usually good to excellent. Many animals suffering from mild cases can be expected to see recovery and reversal of signs and symptoms after treatment. In more severe cases, reversal of permanent damage is typically unlikely, but with treatment, these animals too can be expected to survive and be able to live decent qualities of life despite their crippling lifetime injuries. Ultimately, MBD is an entirely preventable disease by ensuring the correct and proper diets, supplementation, exercise, and adequate exposure to UVB lighting for your reptile or amphibian.
Additional MBD Links and Resources
1. The Green Iguana Society: http://www.greenigsociety.org/mbd.htm
2. Doctors Foster & Smith Pet Education Series: MBD in Reptiles: http://www.drsfostersmith.com/pic/article.cfm?c=6016&articleid=2487
3. The Center for Avian and Exotic Medicine: http://www.drsfostersmith.com/pic/article.cfm?c=6016&articleid=2487
4. PetMD Metabolic Bone Disease and Disorders in Reptiles: http://www.petmd.com/reptile/conditions/musculoskeletal/c_rp_hyperparathyroidism
5. Melissa Kaplan’s Herp Care Collection, Identification and Treatment of Metabolic Bone Disease: http://www.anapsid.org/mbd.html