amyloid arthropathy

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Amyloid arthropathy results from the extracellular deposition of the fibrous protein amyloid within the skeletal system and is a skeletal manifestation of amyloidosis particularly in patients on long term haemodialysis. It may involve either the axial skeleton (especially the cervical spine) or the appendicular skeleton and is distinct from renal osteodystrophy which, however, often co-exists .

Epidemiology

Amyloid arthropathy is usually haemodialysis-related and is therefore encountered in individuals with chronic renal failure on long term dialysis .

Clinical presentation

The clinical presentation varies according to joints that are affected. Commonly, this initially manifests as shoulder pain and carpal tunnel syndrome and symptoms are commonly bilateral.

Patients can also develop osteolytic bone lesions (amyloidomas) and pathological fractures.

Some patients may present with spinal involvement including cord compression or radicular symptoms due to nerve root compression .

Pathology

Amyloid arthropathy results from the deposition of β2-microglobulin, particularly in renal failure patients undergoing long-term haemodialysis.

Pathogenesis is probably multifactorial and relates to the duration of renal failure, patient's age, age at commencing haemodialysis and duration of haemodialysis .

Amyloid protein is not filtered by standard dialysis membranes and tends to accumulate in the musculoskeletal system .

Radiographic features

Plain radiograph

Features of amyloid arthropathy are those of an erosive and destructive osteoarthropathy, involving most commonly the hips, shoulders and carpal bones. Distribution is frequently bilateral.

In the large joints, amyloid arthropathy resembles inflammatory arthritis with :

juxta-articular soft tissue swelling(s)
mild periarticular osteoporosis
juxta-articular and subchondral cystic lesions (geodes), usually with well-defined sclerotic margins
joint space is usually normal in width until late in the course of the disease

Patients with amyloidomas of bone or with large subchondral lesions have a high prevalence of pathologic fractures.

In the spine, the intervertebral discs are affected and are often associated with endplate erosions that can mimic infection . Deposition of amyloid in the ligamentum flava as well as within the synovium of facet joints and atlantooccipital joints and atlantoaxial joints may be seen as erosions .

Ultrasound

In addition to demonstrating thickening of tendons due to infiltration by amyloid (e.g. supraspinatus and biceps tendons), it is also possible to directly visualize amyloid deposits. These appear as an accumulation of echogenic material within or adjacent to joints and between muscles bellies and tendons . Joint effusions and accumulation of fluid around tendons and within bursae are also common .

MRI

The MR imaging appearance of amyloid infiltration within or around the joint consists of extensive deposition of an abnormal soft tissue that usually have the following signal characteristics :

T1: low signal intensity
T2: more variable but usually low to intermediate signal intensity

This abnormal material covers the synovial membrane, fills subchondral defects, and extends to periarticular soft tissue. Joint effusions are usually present.

Differential diagnosis

The differential for multiple lytic bone lesions includes :

The differential for the low signal intensity intra-articular/intra-osseous material includes :

Practical points

typically found in renal failure patients undergoing long-term haemodialysis
periarticular soft tissue swelling, joint effusion, and large subchondral erosions ("cysts")
deposition of abnormal soft tissue with low signal on all MRI sequences
pathologic fracture may occur