Amyloidoma, an Unusual Cause of Fracture

We report a case of a spontaneous hip fracture in a context of dysglobulinemia. The bone histologic examination found amyloidoma. Amyloidoma is an overload pathology and an unusual cause of fracture. In most of the cases, it is associated with myeloma and the difference between bone invasion of myeloma and amyloidoma in an osteolytic radiographic picture is not easy but is of importance because prognosis and treatment may be totally different. Thus, in the context of dysglobulinemia, one must keep in mind that spontaneous bone fracture may be due to amyloidoma with another prognosis.


Introduction
Amyloidoma is an uncommon cause of bone fragility. It occurs in the context of dysglobulinemia and the difference between amyloidoma and myeloma is difficult but is important.

Case
We report the clinical story of an 87-year-old man who was hospitalized for a right hip fracture without high energy trauma. He was known, but not followed up, for a kappa light chain monoclonal gammopathy diagnosed 7 years ago. He had no inflammatory syndrome (CRP < 10 mg/dL and ESR < 25 mm) and no hypercalcemia (<2, 57 mmol/L). The electrophoresis was characterized by an hypogammaglobulinemia and the presence of kappa light chain. The myelogram showed 9% of kappa light chain monoclonal plasmocytes. The Bence Jones proteinuria was positive. He underwent a hip arthroplasty and the histological examination of the femoral head found multifocal non-AA amyloid deposits, with osteolysis and a pseudotumoral aspect (amyloidoma). A biopsy of accessory salivary glands found non-AA amyloid deposits too. The radiographic exam (Figure 1) at the time of the fracture diagnosis showed geodes surrounded by area of osteosclerosis corresponding to focal deposits of amyloid.
The extension statement showed only other geodes in the left hip ( Figure 2). Six months later, he suffered from a contralateral hip fracture probably secondary to amyloidosis too.

Discussion
This is the second observation of hip fracture secondary to amyloidoma [1]. Amyloidoma is an unusual cause of fracture. Amyloidosis is an overload pathology characterized by extra cellular deposits of amyloid substance. The osteoarticular involvement represented by amyloidoma, amyloid arthropathy [2], and amyloid polyarthritis [3] is rare. Few types of amyloidosis are responsible for these manifestations [4]: AL amyloidosis which is primary or associated with myeloma [5], 2-microglobulin amyloidosis which is associated with chronic dialysis [6], and ATTR amyloidosis including the senile and the hereditary amyloidosis.
Amyloidoma is most frequently associated with the AL amyloidosis which is linked with myeloma by the kappa or lambda light chain. These light chains share the same amino acid sequence with the AL amyloid substance [4]. Among these associations, amyloidoma can be a primary pathology, but it is less frequent. In the literature, 35 cases of bone locations (Table 1) are described to date and mainly in the spine. There are 23 vertebral involvements, and 6 are located at the skull. Peripheral involvements are more exceptional. There are just two humeral locations and one femoral [1] location described and finally 3 locations in the belts. This distribution is the same as for myeloma, in the trabecular bone. These locations might be explained by the possible immunoglobulin origin of amyloid proteins and the similarity of the amino acid sequence. The difference between bone invasion of myeloma and amyloidoma in front of an osteolytic lesion is not clear in a patient suffering from myeloma. In case of amyloidoma, we can observe a geode surrounded by osteosclerosis and this osteosclerosis may differentiate between the two conditions. This detail may be interesting in the absence of histologic data. This is important since the treatment and the prognosis are totally different between myeloma lesions and amyloidoma. Thus, in case of fracture in a patient with dysglobulinemia, one must keep in mind the possibility of an amyloidoma, especially in front of a geode surrounded by osteosclerosis.

Disclosure
Frank Verhoeven is the first author.