[IgG-κ lymphoplasmacytic lymphoma complicated by bilateral femoral neck fractures secondary to bone involvement].

Lymphoplasmacytic lymphoma (LPL) is a type of indolent B-cell lymphoma typically associated with IgM paraproteinemia and does not require immediate treatment until symptoms appear. However, non-IgM LPL has a higher frequency of extramedullary involvement and requires more aggressive therapy than IgM-LPL. A 51-year-old woman in treatment-free follow-up for LPL with IgG-κ paraproteinemia was referred to our hospital with a chief complaint of right coxalgia. A plain MRI scan showed multiple osteolytic bone lesions, including bilateral femoral incomplete fractures. Similar bone lesions were also detected in the right shoulder joint. Pathological examination of the bilateral femurs and the right shoulder revealed LPL lesions with amyloid deposits. MYD88 L265P gene mutations were confirmed by genetic analysis, and all lesions were considered identical. Ibrutinib plus rituximab therapy was administered, resulting in a partial response sustained to date. Bone involvement and amyloidosis are rare but critical extranodal manifestations of LPL, necessitating careful screening and follow-up even in asymptomatic patients. When these manifestations are suspected, prompt pathological and genetic evaluation is warranted, especially in non-IgM LPL cases.