1519 - Distinguishing Bizarre Parosteal Osteochondromatous Proliferation from Heterotropic Ossification: Uncommon Differential Diagnosis in Post-Stroke Patients.

Left MCA stroke patient presented with bony mass diagnosed with BPOP, instead of the more commonly expected secondary HO.
 

Case Description: A 29-year-old male with 6-month history of left middle cerebral artery (MCA) stroke and right-sided hemiparesis presented to rehab clinic for spasticity management, was found to have swelling of the right elbow.  Initial evaluation was significant for non-tender bony mass of distal lateral elbow with associated warmth and swelling.  Passive range of motion (ROM) was limited in elbow extension to 170 degrees. Working diagnosis included heterotropic ossification (HO). X-ray and magnetic resonance imaging (MRI) demonstrated a large lobulated, exophytic osseous lesion of distal radius bulging into the triceps, consistent with Bizarre Parosteal Osteochondromatous Proliferation (BPOP). 
 

Discussions:

Heterotropic ossification (HO) is a known post-stroke complication, often presenting as a firm mass limiting range of motion of the elbow. Thus, HO is typically the leading diagnosis. While similar in presentation, the mass in this patient was diagnosed as BPOP, or Nora’s lesion, which is a rare, benign tumor that mimics the clinical and radiographic features of malignant conditions. Although BPOP typically affects the hands and feet, its unusual localization and rarity at the elbow adds to the complexity to clinical evaluation.

The clinical presentation of BPOP makes it a challenging differential diagnosis in patients with known neurological damage. This case emphasizes the importance of considering rare entities like BPOP, especially in context of ruling out malignancy, or when expected response to standard HO treatments is not observed. Surgical management in BPOP aims to address functional limitations of the limb, like approaches used for HO.


Conclusions:

This case highlights the need for a broad differential diagnosis in evaluation of post-stroke complications. While HO is common, rare lesions like BPOP should also be considered to ensure accurate diagnosis and appropriate management.