Systemic Mastocytosis Presenting as Pathologic Intertrochanteric Femur Fracture

Systemic mastocytosis (SM) is pathologically characterized by the proliferation of mast cells with infiltrates in various organs, almost always including bone marrow, leading to defects in bone remodeling. Osteoporosis and subsequent fragility fractures are the most common and clinically relevant presentation, although pathologic fracture through the focal lytic lesions can also be observed. Here, we report the case of a 54-year-old woman, with a recent history of unexplained severe allergic reactions, presenting with intertrochanteric fracture of the left femur which on careful history, physical and radiological evaluation was determined to be pathological. The patient was found to have lytic lesions on the CT scan at the fracture site and the pelvis, bilateral femurs, ribs, and sternum, raising suspicion for malignancy. The malignancy workup failed to reveal a primary neoplasm, and the patient was indicated for intramedullary fixation of the left femur along with intraoperative biopsy. Pathologic evaluation of the femoral biopsy was positive for aggregates of mast cells with CD117 (c-KIT, D816V). This finding prompted a bone marrow biopsy, which ultimately led to the diagnosis of aggressive SM. Femoral intramedullary fixation was done with a trochanteric femoral nail, and the patient was postoperatively started on calcium, vitamin D, and physical therapy. Systemic disease was managed by the hematology-oncology team, and the patient was given an epinephrine autoinjector (EpiPen) and managed with midostaurin (Rydapt, Novartis Pharmaceuticals). Treating surgeons should be aware that a pathological long bone fracture can be the initial presentation of SM. Furthermore, surgeons should consider following patients with SM for longer than usual considering a higher risk of complications, such as implant loosening, nonunion, and refracture due to poor and progressively worsening quality of the bone. Our patient was followed with routine visits for 30 months and showed no clinical or radiographical signs of any complications.