Solution to Unknown Case #15 – Osteogenesis Imperfecta and the Differential Diagnosis of Gracile Diaphyses

History: 17 year old female. History withheld. 

Osteogenesis Imperfecta: Radiograph of the bilateral lower extremities reveals marked bowing deformities of the femurs, tibias, and fibulas with a background of diffuse osteopenia. The tibia and fibula also have gracile diaphyses.

This is a case of osteogenesis imperfecta. Osteogenesis imperfecta is a genetic defect in forming type 1 collagen. There are multiple subtypes of osteogenesis imperfecta, which are divided according to the Silence classificaiton system as follows:

Type 1 – Autosomal Dominant, blue sclerae, mildest form (often called osteogenesis imperfecta tarda), 50% will have hearing loss

Type 2 – Autosomal Recessive, blue sclerae, lethal in perinatal period

Type 3 – Autosomal Recessive, normal sclerae, fractures at birth, most severe form that is non lethal.

Type 4 – Autosomal Dominant, normal sclerae, moderate deformities, normal hearing

There are more complex classification characteristics that have been added since the Silence classification system originally was published. Those can be read about here.

The interesting finding on the image above is what is called gracile (meaning slender) diaphyses. The differential diagnosis of gracile diaphyses is as follows:

1. Paralysis or disuse

2. Juvenile idiopathic arthritis

3. Neurofibromatosis

4. Marfan Syndrome

5. Hemophilia

6. Osteogenesis imperfecta

7. Muscular Dystrophy

8. Arthrogryposis

There are many more rare entities that cause gracile diaphyses which aren’t worth mentioning.

Read about basilar invagination in a patient with osteogenesis imperfecta.

Read about cochlear otosclerosis in a patient with osteogenesis imperfecta.