Answer:  Dialysis-related amyloidosis

Findings:

Conventional radiograph shows erosion with intraosseous cystic lesion at the left femoral head.

CT shows erosions at the left femoral head with prominent thickening at the bilateral hip joint capsule.

MRI reveals prominent thickening at the bilateral hip joint capsule with intermediate to hypointense signal and erosions at the left proximal femur.

Differential Diagnosis:  

Pigmented villonodular synovitis

Hemophilic arthropathy

Diagnosis:  

Dialysis-related amyloidosis

Discussion:  

Dialysis-related amyloidosis is a unique type of amyloidosis affecting patients undergoing long-term hemodialysis. It occurs secondarily to the deposition of β2-microglobulin, and the mechanism of amyloid fibril formation from β2-microglobulin is still unknown.  

Dialysis-related amyloidosis predominantly involves the osteoarticular system and is clinically manifested by erosive and destructive osteoarthropathies, destructive spondyloarthropathy, and carpal tunnel syndrome. The common sites of involvement are hips, wrists, shoulders, knees,

and spine. In contrast to other types of amyloidosis (e.g., reactive amyloidosis due to multiplemyeloma), the visceral form is believed to have a low incidence and to occur late in the course of the disease.

Conventional radiograph:

Bone lesions show radiolucencies of variable size within the medullary or cortical bone that may cause cortical destruction.  

MRI:

MRI allows assessment of intraosseous, periarticular, and soft-tissue involvement. In most patients, bone lesions show decreased signal intensity on T1-weighted images and various signal intensity on T2-weighted images. Identification of an intraosseous lesion with relatively low signal intensity on both T1- and T2-weighted images is helpful in the diagnosis of amyloidosis. Synovial thickening can also be identified. In the intraarticular spaces, nodular lesions appear with decreased or intermediate signal intensity on T1-weighted images anddecreased signal intensity on T2-weighted images. Amyloid deposits in bursa result in bursitis.

In patients undergoing long-term hemodialysis, cystic and destructive lesions on conventional radiographs, soft-tissue abnormalities in intra- or periarticular structures with relatively low-signal-intensity masses on T2-weighted MR images should raise the suspicion of dialysis-related amyloidosis.

References:

 Kiss E, Keusch G, Zanetti M, et al. Dialysis-related amyloidosis revisited. Am J Roentgenol 2005;185(6):1460-1467.