DISTINCTIVE CKD-MBD CHANGES
SECONDARY AND TERTIARY HYPERPARATHYROIDISM
Predominant feature of HPT is an increased bone turnover with rapid bone resorption being its hallmark.
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Bone resorption
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several types of bone resorption are recognized [Tbl.1].
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in 95% of patients with HPT, earliest and most typical skeletal changes develop in the hand -> hand radiographs are used both for confirmation of diagnosis and evaluation of treatment response
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in the remaining 5%, the hands can be normal, while initial features of bone resorption will be present in other skeletal regions [Fig.5-8].
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Brown tumour (osteoclastoma)
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nonneoplastic focus of intensive bone resorption/remodelling
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histopathology: hypervascular fibroblastic stroma, foci of hemorrhage (hemosiderin deposits), and accumulation of osteoclastic multinucleated giant cells.
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rare (1.5 % of patients with secondary HPT) - HPT is usually detected and treated before brown tumours occur
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usually asymptomatic, found incidentally on X-ray/CT; larger lesions may cause pathologic fractures
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common appearance [Fig.9-11,16]
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single or multiple
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may occur in any bone (common locations: mandible, ribs, clavicle, pelvis, femur) and any part of bone (including articular ends)
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eccentric or cortical
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well-defined, expansive, unicameral or multilobulated osteolytic lesion (IB/II in Lodwick-Madewell Grading System), after HPT treatment evolves into mixed lytic/ sclerotic lesion
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periosteal reactions suggest fracture
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MRI appearance reflects lesion composition and presence of blood products
[Tbl.2]
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DD: metastases (rare in articular ends and cortex), other giant cell-containing lesions (correlation with hypercalcaemia and HPT important)
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Periosteal reaction (neostasis)
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unusual, associated with severe disease
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continuous, lamellated, after being incorporated into adjacent bone results in cortical thickening
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typical locations: long and short tubular bones, pubic rami along the iliopectineal line
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Soft tissue calcification (-> “Crystal deposition disease”)
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Complications:
OSTEOPENIA
Cumulative effect of osteomalacia (inadequate or abnormal mineralization of osteoid due to vitamin D deficiency), bone resorption (HPT), and osteoporosis (including drug-induced osteoporosis). The most important complication of osteopenia are INSUFFICIENCY FRACTURES. The risk of fracture is up to 5 times higher in individuals with eGFR 60 ml/min per 1.73 m2. Osteoporosis occurs in about 30% of post-transplant population, 1/5th of patients will experience a fracture within the first 5 years following transplantation, especially during initial 6 months when Ca/Pi metabolism disturbances are most pronounced [Fig.12(1e)]. Cyclosporine and glucocorticosteroids are important drugs responsible for bone loss. The steroid withdrawal protocols lead to a 31% fracture risk reduction.
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indistinct trabecular bone appearance giving the impression of a “poor-quality” radiograph
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insufficiency fractures typically occur bilaterally in a symmetric fashion
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frequent locations[Fig.13-14]:
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thoracic and lumbar vertebrae - crush/wedge fractures
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femoral neck
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pelvis: pubic rami, sacrum (Honda sign), supraacetabular region
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less common locations:
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sternum, scapular neck, ribs, proximal third of femur, tibia and fibula, talus
Looser-Milkman zones are a type of insufficiency fracture pathognomonic for osteomalacia [Fig.15-19]
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transverse lucencies traversing part way through bone, perpendicularly to the involved cortex/load-bearing trabeculae
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may progress to complete fracture
DIFFUSE BONY SCLEROSIS
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Shows a strong predilection for the skeletal sites with a predominance of trabecular over cortical bone: spine (classic “rugger jersey” spine), pelvis, ribs, and clavicles. [Fig.20]
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The bone is structurally weak and prone to stress fractures.
CRYSTAL DEPOSITION DISEASE
Deposits of calcium salts can occur in any soft tissue, typically around joints.
Contributing factors: hypercalcemia, local tissue damage, alkalosis, and an increase in the calcium-phosphorus product in the extracellular fluid.
Ultrasound is the most sensitive diagnostic tool in detecting early calcium deposits and tissue inflammation.
DD includes a wide range of disorders causing predominantly periarticular calcifications [Tbl.4]
DISTINCTIVE DIALYSIS-RELATED CHANGES
AMYLOIDOSIS
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occurs secondarily to the extracellular deposition of β2-microglobulin
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affects 20% of patients receiving HD for 2–4 years, and 100% of patients after 13 years of HD.
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mainly involves the osteoarticular system (bone, synovium, muscle, tendon, ligaments)
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spectrum of clinical and imaging findings is diverse [Tbl.5] [Fig.26-30]
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Complications:
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ALUMINUM INTOXICATION
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Very rare
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Osteomalacia with insufficiency fractures of upper ribs (more common than in osteomalacia from other causes), vertebrae, hips, and pelvis
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Avascular necrosis
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Periosteal reactions along the distal shafts of the tibia and fibula and in the pelvic inlet
IMMUNOSUPRESSION-RELATED BONE CHANGES
OSTEONECROSIS
Patients taking glucocorticosteroids, cyclosporine, sirolimus, and azathioprine are at higher risk of bone necrosis.
Location:
femoral and humeral head, distal femur, proximal tibia, talar dome, humeral condyles, cuboid and carpal bones.
When in subarticular region, commonly leads to the collapse of articular surface (due to accumulation of microfractures) and secondary osteoarthritis.
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X-ray/CT: [Fig.31-32]
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first sign: subtle widening of joint cavity due to effusion and periarticular osteoporosis
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serpentine rim of sclerosis around the lucent area
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crescent sign - a lucent line in the subarticular bone representing early subchondral collapse and separation from the overlying cartilage
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collapse of the articular surface with its flattening
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MRI: [Fig.33]
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first sign: reactive interface line - serpentine low signal line around typically fatty center
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contents other than fat: hemorrhage (high signal on T1WI and T2WI), cystic areas (low signal on T1WI, high on T2WI), and fibrous tissue (low signal).
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diffuse bone marrow edema
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double line sign: common sign - peripheral dark line (sclerosis) and inner bright (granulation tissue) surrounding the lesion on T2WI
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rim sign: osteochondral fragmentation; high T2 or intermediate T1 signal line (fluid) between two low signal lines (sclerosis) - implies instability
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T1 C+(Gd): peripheral rim of enhancement (granulation tissue)
Immunocompromised patients demonstrate higher risk of osseous MALIGNANCY and INFECTIONS (osteomyelitis and septic arthritis caused by both non- and opportunistic pathogens).