Filly's 4th Law
Even among the rarest of diseases, some are much more common than others.
When I decided that I would focus my career in ultrasound I thought to myself, ultrasound is nearly useless in bone diseases so, at least, I won’t need to know those rare skeletal dysplasias. Indeed, if I asked you to list imaging procedures from best to worst with regard to skeletal imaging I might see arguments about which modality is number 1: radiography, MRI, or CT. But everyone would list sonography in last place. For good or for bad, fate took a nasty turn for me and somehow I was forced to become “an expert” in the prenatal diagnosis of skeletal dysplasias.
There are approximately 400 skeletal dysplasias. As I said, I am considered an “expert” and doubt that I could name 20 of them. In a 40-year career as an “expert” in prenatal diagnosis I would doubt that I saw 20 different skeletal dysplasias. Had I practiced another 100 years I doubt I would have doubled that number.
My salvation in this endeavor was wrapped up in the title of this “Law,” Even among the rarest of diseases, some are much more common than others.
In a 23-center experience with prenatal diagnosis of skeletal dysplasias the results showed the following:
- Thanatophoric dysplasia 43 cases
- Osteogenesis imperfect: Type II 35 cases
- Heterozygous achondroplasia 15 cases
- Achondrogenesis 9 cases
- Other recognizable syndromes 37 cases
Total 139 cases
As you can see, the top three diagnoses constituted two-thirds of all cases. And do not fail to notice that among 23 prenatal diagnostic centers only 41 of the possible 400 known skeletal dysplasias were even seen once!