Trabecular bone loss occurs preferentially among the trabeculae that get the least stress. In the cortex, bone may be lost along the endosteal or subperiosteal surfaces, or may be lost along the surface of the Haversian canals (cortical tunnelling). Where is this bone lost? It occurs in both cortical and trabecular bone. Men lose about 0.4 % of their skeletal mass per year after age 50 Women lose about 0.75 – 1.0 % of their skeletal mass per year after age 35 - this may accelerate to as much as 2 – 3 % per year following the menopause This bone loss accelerates in women following the menopause, as shown below. In general, the gradual loss of skeletal mass begins in women in the fourth decade and in the fifth or sixth decade of life for men. The pathogenesis of both of these states is not clear, but probably involves a combination of decreased bone production and increased resorption. Both of these processes are very common, and both commonly occur in the same individuals, so the two entities are often lumped together. Postmenopausal osteoporosis refers to the increased bone loss seen in women following menopause. Senile osteoporosis simply refers to the gradual loss of skeletal mass that is seen with advancing age. These two entities are the most common causes of generalized osteoporosis. Let’s look as some of these causes in more detail. After that, I personally lump everything else into one big category and consult the VINDICATE differential. The next most common cause is probably drugs (steroids) or dietary deficiency (calcium). The most common causes are senile and postmenopausal osteoporosis. The reason for this is that the entities listed above are not in the order that one is most likely to see them. This VINDICATE differential diagnosis may be helpful for recalling unusual causes of osteoporosis, but it is not as useful as it could be for the radiologist’s everyday life. Mnemonic = VINDICATE Differential Diagnosis of Osteopenia Some of the major ones are listed in the table below. There are many causes of generalized osteoporosis. The differential diagnosis for generalized osteoporosis is a bit longer and more complex. The differential diagnosis for regional osteoporosis is a fairly short and manageable one. What are these usual patterns? The main two types are generalized osteoporosis and localized (regional) osteoporosis. Once one gets used to the seeing these patterns, then deviations from the usual patterns will begin to stand out, and one can suggest to a clinician that further workup may be indicated in these cases. In these days of cost containment, this should be a sobering thought.Ī good place to start might be with recognition of the usual patterns of osteopenia seen in everyday life. Also remember that if all you ever do is blindly apply a bunch of 95 % rules, you can be replaced by a file room clerk with a rubber stamp. Remember that 95 % diagnostic accuracy is easier to accept if you and your family are not in the other 5 %. This may not be a bad strategy for the larval radiologist, but as you move up the radiologic food chain, you should strive to do better than this. In fact, if you just dropped the term osteopenia and used the term osteoporosis instead, you would be right about 95 % of the time, which is not a bad batting average. Osteoporosis is, by far, the most likely cause of osteopenia. The approach to osteopenia can be simplified greatly, if one forgets all causes except osteoporosis. Resnick has made the statement that “You can take a normal patient and an abnormal X-ray technician, and give the patient osteoporosis at will.” Approach Finally, differences in radiographic technique can widely alter the radiologist’s perception of whether or not osteopenia is present. Another problem with plain films is the lack of some standard by which to compare the area of interest. One must lose 30 – 50 % of the bone mass before it can be detected on a plain film. First of all, plain films are hideously insensitive to changes in bone mineral. It can be fairly difficult to diagnose osteopenia accurately on plain radiographs. For example, the table below shows several disorders that can produce osteopenia, as well as more specific radiographic clues to their diagnosis. Rather, it prompts a search for other more specific clues to the exact underlying disorder. However, there are many disease entities that can cause osteopenia, so the mere finding of radiolucent bone does not make this an automatic diagnosis. The most common cause by far of osteopenia is osteoporosis. This term is much preferred over terms such as “demineralization” or “undermineralization”, since we really can’t tell the exact mineral status of the patient’s bone from the radiograph alone. One of the most common findings in skeletal radiology is increased radiolucency of bone, most properly termed osteopenia.
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