Radiologic Findings in Polyarticular Amyloid Arthropathy and Myopathy in Multiple Myeloma: A Case Report

BACKGROUND Amyloid arthropathy and myopathy are complications of amyloidosis that can be associated with non-specific imaging findings, which may be challenging to interpret. The report is of a case of polyarticular amyloid arthropathy and myopathy in a 56-year-old man with multiple myeloma and includes a description of the radiographic, computed tomography (CT), and magnetic resonance imaging (MRI) findings. CASE REPORT A 56-year-old man with multiple myeloma presented with chronic polyarticular pain and swelling. Soft tissue thickening of the wrist and knee were found on MRI to be of intermediate T1 weighted imaging (T1WI) and low to intermediate T2 weighted imaging (T2WI) signal intensity. Denervation muscle edema seen in the thenar muscles on the MRI of the right wrist were associated with carpal tunnel syndrome secondary to amyloid deposition. Soft tissue lesions in the periarticular regions of both hip joints were contiguous with subchondral bone lesions. Diffusely scattered myeloma lesions were shown as hyperintense on short tau inversion recovery (STIR) MRI imaging throughout the appendicular and axial skeleton, with vertebral compression fractures. Bilateral iliopsoas involvement with hypertrophy and abnormal surrounding fat reticulated signal intensity was consistent with amyloid myopathy. The patient had a pathological fracture of the right femoral neck and underwent surgical fixation. Histology of the right femoral head confirmed amyloid deposits. CONCLUSIONS Because the clinical presentation and imaging findings of musculoskeletal amyloidosis can be nonspecific, they can result in delay in diagnosis and treatment. Early radiologic identification of polyarticular amyloid arthropathy and myopathy should prompt confirmatory biopsy to confirm the diagnosis.