Teaching Case

17-year-old male patient without significant past medical history presenting with right third digit laceration. The patient had cut his finger on a metal window frame. No numbness or weakness. Denies any other injuries. Comparison radiograph from when the patient was 6 years old are available.

Plain radiographs of the right hand, taken nearly a decade apart. Images show dramatic increase in quantity and extent of multiple sclerotic lesions in the radius and ulna, carpal bones, metacarpals and phalanges. The bones have otherwise normal mineralization.

Of note, Figure 2 also shows evidence of soft tissue injury and laceration.

Background
Osteopoikilosis is a rare, benign condition characterized by multiple sclerotic foci, typically seen in the appendicular skeleton and the pelvis. It has an autosomal dominant inheritance pattern, linked to a loss-of-function mutation in LEMD3 (LEM domain containing 3). The LEMD3 gene encodes for Man1, an inner nuclear membrane protein. The mechanisms by which Man1 dysfunction leads to the phenotypical manifestations of osteopoikilosis are not yet known [1].

Clinical Perspective
Osteopoikilosis is seen in all age groups and affects both genders without partiality. It is usually an incidental radiographic finding. As such, it is typically asymptomatic, but may be associated with joint pain and effusions [2]. It does not have malignant potential but may be confused with osteoblastic metastases. To avoid unnecessary testing, radiologists should be made aware of this condition’s benign nature [2]. Osteopoikilosis is a feature of Buschke-Ollendorf syndrome (BOS), but it also appears independent of BOS [1]. As a part of the sclerosing bone dysplasia disorders, osteopoikilosis is often concurrently found with melorheostosis and osteopathia striata [3].

Imaging Perspective
The sclerotic lesions seen in osteopoikilosis are bone islands (enostoses), and therefore demonstrate the usual characteristics one would expect. On plain film and CT, jagged edges that blend into the surrounding bony trabeculae are appreciated. The enostoses have the same long axes as the bones that they are found in. They are predominantly found in the epiphyses and metaphysis, with a propensity for regions around joints [4]. Imaging evidence of a dramatic increase in quantity and extent of sclerotic foci is rarely documented. The appearance on MR follows mature dense bone, which shows low signal on both T1 and T2 weighted images. There is no signal enhancement following contrast administration [5].

Outcome
One should be mindful when raising the differential diagnosis based on these radiographic findings. It may lead to unnecessarily workup that could potentially lead to unnecessary surgery. A teaching point from comparing these two studies, is the benign progression of osteopoikilosis. Radiographic evidence that demonstrates the progression of this condition is rare in the literature.

Teaching Points
1. Osteopoikilosis is a rare, autosomal dominantly inherited condition. It is typically asymptomatic and is incidentally found on radiographs.
2. This case demonstrates the rarely documented benign progression of osteopoikilosis.
3. Osteopoikilosis does not require further workup, but may be found in association with bone or skin disorders.