Bone and Soft-Tissue Disorders
= extracellular deposition of a chemically diverse group of protein polysaccharides in body tissues (abnormal folding + assembly of β2-microglobulin); tends to form around capillaries + endothelial cells of larger blood vessels causing ultimately vascular obliteration with infarction
β2-microglobulin = low-molecular-weight serum protein not filtered by standard dialysis membranes
Incidence: 6–10÷100,000 annually in USA + western Europe
Path: stains with Congo red
At risk: patients on long-term hemodialysis
- bone pain (eg, shoulder pain)
- periarticular rubbery soft-tissue swelling + stiffness (shoulders, hips, fingers):
- carpal-tunnel syndrome (commonly bilateral)
- Bence-Jones protein (without myeloma)
= synovial-articular pattern of amyloidosis
Associated with: chronic hemodialysis, plasma cell dyscrasia, rheumatoid arthritis, familial Mediterranean fever, chronic osteomyelitis
Location: cervical spine, hip, shoulder, elbow, knee, wrist; bilateral
- juxtaarticular soft-tissue masses (amyloid deposited in synovium, joint capsule, tendons, ligaments) ± extrinsic osseous erosion
- mild periarticular osteopenia
- subchondral cysts + well-defined sclerotic margin
- joint effusion
- joint space preserved until late in course of disease
- subluxation of proximal humerus + femoral neck
MR:
- extensive deposition of abnormal soft tissue of low to intermediate SI on T1WI + T2WI covering synovial membrane, filling subchondral defects, extending into periarticular tissue
- low SI on T1WI + T2WI subjacent to vertebral endplates in lower cervical >thoracic / lumbar spine
- joint effusion
DDx: inflammatory arthritis, PVNS
Diffuse Amyloid Marrow Deposition 
- generalized osteoporosis
- coarse trabecular pattern (DDx: sarcoidosis)
- pathologic collapse of vertebral body may occur
= localized destructive lesion of amyloidosis (rarest form)
Location: appendicular >axial skeleton
- focal medullary lytic lesion with endosteal scalloping (± secondary invasion + erosion of articular bone)
Cx: pathologic fracture