High Yield Overview
RENAL OSTEODYSTROPHY
CKD-Mineral Bone Disorder | Secondary Hyperparathyroidism | Mixed Bone Disease
90%of dialysis patients have bone disease
2-4xincreased fracture risk in CKD
PTH 2-9xtarget PTH elevation for CKD stage
1.5 mmol/Ltarget phosphate control threshold
RENAL OSTEODYSTROPHY SPECTRUM
Osteitis Fibrosa Cystica
PatternHigh-turnover bone disease from secondary HPT
TreatmentVitamin D, calcimimetics, parathyroidectomy
Adynamic Bone Disease
PatternLow-turnover from oversuppressed PTH
TreatmentReduce vitamin D, reduce calcium binders
Mixed Disease
PatternFeatures of both high and low turnover
TreatmentBalanced approach, individualized
Critical Must-Knows
- CKD-MBD = chronic kidney disease mineral and bone disorder (umbrella term for bone, vascular, biochemical abnormalities)
- Pathogenesis: Phosphate retention and reduced calcitriol production lead to hypocalcemia and secondary hyperparathyroidism
- Rugger jersey spine = dense vertebral endplates (sandwich vertebrae) from subperiosteal bone formation
- Target PTH 2-9 times upper limit normal for CKD stage (not normal PTH - oversuppression causes adynamic bone)
- Vascular calcification is major complication - calcium-phosphate product should be less than 4.4 mmol squared per L squared
Examiner's Pearls
- "Secondary HPT in CKD is APPROPRIATE - do not parathyroidectomy unless medical management fails
- "Distinguish from primary HPT: CKD has low/normal calcium, primary HPT has high calcium
- "Adynamic bone disease from oversuppression - paradoxically increases fracture risk
- "Calciphylaxis is life-threatening vascular calcification (50% mortality) - avoid calcium-based phosphate binders if occurs
Clinical Imaging
Imaging Gallery
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Critical Renal Osteodystrophy Exam Points
Pathogenesis Triad
Three key defects in CKD: (1) Phosphate retention (reduced renal excretion), (2) Reduced 1-alpha hydroxylation (kidney is site of activation of vitamin D to calcitriol), (3) Hypocalcemia (reduced intestinal calcium absorption). These drive secondary hyperparathyroidism as compensatory mechanism.
Spectrum of Bone Disease
High-turnover (osteitis fibrosa cystica) from severe secondary HPT - brown tumors, subperiosteal resorption. Low-turnover (adynamic bone) from oversuppressed PTH - paradoxically increased fracture risk. Mixed disease - most common, features of both. Cannot distinguish on imaging alone - bone biopsy gold standard.
PTH Target Is NOT Normal
Target PTH 2-9 times upper limit normal for CKD stage (NOT normal PTH). Example: CKD Stage 5 (dialysis) target PTH 150-300 pg/mL (normal is 10-65 pg/mL). Oversuppressing PTH to normal causes adynamic bone disease - low bone turnover, increased fracture risk, impaired bone healing.
Vascular Calcification Risk
Calcium-phosphate product greater than 4.4 mmol squared per L squared increases vascular calcification risk. Calcify heart valves, coronary arteries, peripheral vessels. Calciphylaxis (calcific uremic arteriolopathy) is life-threatening - painful skin necrosis from arteriolar calcification, 50% mortality. Avoid calcium-based phosphate binders if occurs.
At a Glance
Renal osteodystrophy (part of CKD-MBD) affects 90% of dialysis patients with bone disease. The pathogenesis triad is: phosphate retention, reduced calcitriol production, and hypocalcemia, driving secondary hyperparathyroidism. The bone disease spectrum ranges from osteitis fibrosa cystica (high-turnover, brown tumors) to adynamic bone disease (low-turnover from oversuppressed PTH—paradoxically increases fracture risk). The radiographic rugger jersey spine (dense vertebral endplates) is pathognomonic. Target PTH is 2-9× upper limit normal (NOT normal—oversuppression is harmful). Monitor the calcium-phosphate product (keep under 4.4 mmol²/L²) to prevent vascular calcification; calciphylaxis carries 50% mortality.
Mnemonic
KIDNEYSPathogenesis of Renal Osteodystrophy
K
Kidney failure
Chronic kidney disease (CKD) is the primary cause
I
Impaired 1-alpha hydroxylation
Reduced conversion of 25-OH vitamin D to active 1,25-dihydroxy form
D
Decreased calcium absorption
Low calcitriol causes reduced intestinal calcium uptake
N
No phosphate excretion
Phosphate retention from reduced GFR leads to hyperphosphatemia
E
Elevated PTH
Secondary hyperparathyroidism compensates for hypocalcemia
Y
Yielding bone disease
Osteitis fibrosa cystica (high-turnover) or adynamic bone (low-turnover)
S
Soft tissue calcification
Vascular calcification from elevated calcium-phosphate product
Memory Hook:Remember KIDNEYS fail, causing the cascade of mineral and bone disease!
Mnemonic
PHOSPHATEMedical Management of CKD-MBD
P
Phosphate binders
Calcium-based (calcium carbonate) or non-calcium (sevelamer, lanthanum)
H
Hydroxylated vitamin D
Activated vitamin D (calcitriol, paricalcitol) to suppress PTH
O
Optimize calcium
Target 2.2-2.5 mmol/L (not too high - risk of vascular calcification)
S
Suppress PTH appropriately
Target 2-9x upper limit normal for CKD stage (NOT normal PTH)
P
Prevent vascular calcification
Keep calcium-phosphate product less than 4.4 mmol squared per L squared
H
Hemodialysis optimization
Adequate dialysis removes phosphate, maintains mineral balance
A
Avoid oversuppression
Adynamic bone disease from excessive PTH suppression increases fracture risk
T
Target phosphate less than 1.5
Dietary restriction plus binders to control hyperphosphatemia
E
Evaluate for calcimimetics
Cinacalcet if refractory secondary HPT (PTH persistently elevated)
Memory Hook:Control PHOSPHATE to manage renal osteodystrophy!
Mnemonic
RUGGERRadiographic Features of Renal Osteodystrophy
R
Rugger jersey spine
Dense vertebral endplates (sandwich vertebrae) from subperiosteal bone formation
U
Under-modeling
Widened bone shafts from impaired remodeling
G
Ground glass skull
Loss of skull trabeculation (salt and pepper appearance)
G
Growth plate abnormalities
Rickets-like changes in children with CKD
E
Erosions subperiosteal
Radial side of middle phalanges (secondary HPT finding)
R
Resorption brown tumors
Lytic lesions from severe secondary hyperparathyroidism
Memory Hook:RUGGER jersey spine is pathognomonic for renal osteodystrophy!
Overview and Epidemiology
Definition
Renal osteodystrophy is the bone component of CKD-MBD (chronic kidney disease mineral and bone disorder), an umbrella term encompassing:
- Bone abnormalities - altered bone turnover, mineralization, volume, strength (renal osteodystrophy)
- Vascular/soft tissue calcification - calcium deposition in vessels, heart valves, soft tissues
- Biochemical abnormalities - disorders of calcium, phosphate, PTH, vitamin D metabolism
Renal osteodystrophy specifically refers to the spectrum of bone diseases that develop in chronic kidney disease, ranging from high-turnover (osteitis fibrosa cystica) to low-turnover (adynamic bone disease) states.
Epidemiology
Prevalence:
- CKD Stage 3-4: 30-50% have secondary hyperparathyroidism and early bone disease
- CKD Stage 5 (dialysis): 90% have histological evidence of renal osteodystrophy
- Fracture incidence: 2-4 times higher than age-matched general population
- Vascular calcification: Present in 80% of dialysis patients
Risk factors for severe bone disease:
- Duration of CKD - longer duration, greater severity
- Dialysis vintage - longer time on dialysis associated with more bone disease
- Poor phosphate control - hyperphosphatemia drives PTH elevation
- Inadequate vitamin D replacement
- Aluminum exposure - historical cause of adynamic bone (now rare)
Pathophysiology
Cascade of CKD-MBD
Primary Defects in CKD
- Reduced GFR leads to phosphate retention (kidneys cannot excrete phosphate)
- Impaired 1-alpha hydroxylase (kidney enzyme) reduces active vitamin D (calcitriol) production
- Reduced intestinal calcium absorption (low calcitriol) causes hypocalcemia
- FGF23 elevation (compensatory) further suppresses calcitriol and increases phosphate excretion (early CKD)
Compensatory Response
- Secondary hyperparathyroidism develops to maintain serum calcium
- PTH-mediated bone resorption releases calcium from skeleton
- PTH-mediated phosphate wasting (limited by reduced GFR)
- Skeletal resistance to PTH develops over time (parathyroid glands enlarge, become autonomous)
Progressive pathway:
- Early CKD (Stage 1-2): FGF23 elevates, phosphate normal, PTH begins to rise
- CKD Stage 3: Hyperphosphatemia develops, PTH rises significantly, calcitriol falls
- CKD Stage 4: Severe secondary hyperparathyroidism, high bone turnover (osteitis fibrosa)
- CKD Stage 5 (dialysis): Mixed bone disease, vascular calcification, skeletal fragility
- Post-transplant: May develop tertiary hyperparathyroidism (autonomous PTH secretion)
Spectrum of Bone Disease
Renal Osteodystrophy Bone Disease Spectrum
| Type | Bone Turnover | PTH Level | Pathophysiology | Treatment |
|---|---|---|---|---|
| Osteitis Fibrosa Cystica | High turnover | Very high (greater than 800 pg/mL) | Severe secondary HPT, excessive bone resorption | Vitamin D, calcimimetics, parathyroidectomy |
| Adynamic Bone Disease | Low turnover | Low or normal | Oversuppressed PTH, impaired bone formation | Reduce vitamin D, reduce calcium intake |
| Mixed Uremic Osteodystrophy | Mixed features | Moderately elevated | Combination of high and low turnover | Balanced approach, individualized |
| Osteomalacia (Rare) | Low turnover | Variable | Vitamin D deficiency, aluminum toxicity (historical) | Vitamin D replacement, remove aluminum |
Target PTH Is NOT Normal in CKD
In CKD, the target PTH is 2-9 times the upper limit of normal for the CKD stage, NOT normal PTH. Example: For CKD Stage 5 (dialysis), target PTH is 150-300 pg/mL (normal is 10-65 pg/mL). Why? Because CKD patients have skeletal resistance to PTH - they need higher PTH to maintain bone turnover. Suppressing PTH to normal causes adynamic bone disease (low turnover bone) which paradoxically increases fracture risk and impairs bone healing.
Vascular Calcification
Mechanism:
- Elevated calcium-phosphate product (Ca x PO4 greater than 4.4 mmol squared per L squared)
- Calcium hydroxyapatite precipitates in vessel walls, heart valves, soft tissues
- Transformation of vascular smooth muscle cells to osteoblast-like cells
- Mediated by uremic toxins, inflammation, oxidative stress
Clinical consequences:
- Vascular calcification - coronary arteries, peripheral vessels (increased cardiovascular mortality)
- Valvular calcification - aortic stenosis, mitral regurgitation
- Calciphylaxis (calcific uremic arteriolopathy) - life-threatening arteriolar calcification with painful skin necrosis, 50% mortality
Classification
Bone Disease Spectrum Classification
By Bone Turnover:
- High-Turnover (Osteitis Fibrosa Cystica): Severe secondary hyperparathyroidism driving excessive bone resorption
- Low-Turnover (Adynamic Bone Disease): Oversuppressed PTH causing reduced bone formation
- Mixed Uremic Osteodystrophy: Combined features, most common type
TMV Classification (Bone Biopsy):
- T = Turnover (high, normal, low)
- M = Mineralization (normal, abnormal)
- V = Volume (high, normal, low)
Clinical Classification:
- Mild: Biochemical abnormalities only, no symptoms
- Moderate: Bone pain, fracture risk, radiographic changes
- Severe: Brown tumors, pathological fractures, calciphylaxis
Clinical Presentation
Symptoms
Bone pain:
- Diffuse bone pain - worse with weight-bearing, activity
- Joint pain - secondary to renal osteodystrophy or crystal arthropathy (gout, pseudogout)
- Pathological fractures - minimal trauma, increased risk 2-4 times general population
- Skeletal deformities - in children with CKD (rickets-like changes)
High-turnover disease (osteitis fibrosa):
- Brown tumors (lytic lesions) - jaw, ribs, pelvis, long bones
- Bone pain and tenderness
- Pathological fractures at brown tumor sites
- Rarely: pruritus (itching from calcium-phosphate deposition in skin)
Low-turnover disease (adynamic bone):
- Often asymptomatic
- Increased fracture risk despite absence of pain
- Poor bone healing after fracture
- Increased risk of hypercalcemia (reduced buffering capacity)
Additional information is provided within the section.
Examination Findings
Musculoskeletal:
- Bone tenderness - sternum, ribs, long bones
- Skeletal deformities - in children (rickets-like bowing, short stature)
- Pathological fractures - vertebral compression, proximal femur
- Proximal muscle weakness - from concurrent vitamin D deficiency or uremic myopathy
Vascular:
- Calcified arteries - palpable, hardened peripheral vessels
- Vascular bruits - from stenotic calcified vessels
- Peripheral ischemia - cool extremities, poor pulses, gangrene (severe cases)
Skin:
- Pruritus - scratch marks, excoriations
- Calciphylaxis lesions - painful, violaceous plaques with central necrosis
Investigations
Laboratory Investigations
Biochemical monitoring in CKD-MBD:
Target Biochemistry in CKD Stages
| Parameter | CKD Stage 3-4 | CKD Stage 5 (Dialysis) | Rationale |
|---|---|---|---|
| Calcium | 2.2-2.5 mmol/L (normal range) | 2.2-2.5 mmol/L | Avoid hypercalcemia (vascular calcification risk) |
| Phosphate | 0.8-1.5 mmol/L | Less than 1.5 mmol/L | Control hyperphosphatemia to reduce PTH drive |
| PTH | 2-4x upper limit normal | 2-9x upper limit normal (150-300 pg/mL) | Maintain bone turnover, avoid adynamic bone |
| 25-OH vitamin D | Greater than 75 nmol/L | Greater than 75 nmol/L | Adequate substrate for calcitriol production |
| Alkaline phosphatase | Monitor trend | Monitor trend | Marker of bone turnover (high in osteitis fibrosa) |
| Ca x PO4 product | Less than 4.4 mmol squared per L squared | Less than 4.4 mmol squared per L squared | Prevent vascular calcification |
Additional investigations:
- Bone-specific alkaline phosphatase - marker of bone formation (high in high-turnover disease)
- FGF23 - elevated early in CKD, promotes phosphate excretion
- Sclerostin - elevated in CKD, inhibits bone formation
- Albumin-corrected calcium - adjust for hypoalbuminemia
Frequency of monitoring:
- CKD Stage 3: Calcium, phosphate, PTH every 6-12 months
- CKD Stage 4: Every 3-6 months
- CKD Stage 5 (dialysis): Monthly calcium and phosphate, PTH every 3 months
Imaging Studies
Plain radiographs:
High-Turnover Disease Features
- Subperiosteal resorption: Radial side of middle phalanges (hand X-ray) - pathognomonic
- Rugger jersey spine: Dense vertebral endplates (sandwich vertebrae) from subperiosteal bone formation
- Salt and pepper skull: Granular loss of skull trabeculation
- Brown tumors: Lytic expansile lesions (jaw, ribs, pelvis)
- Bone cysts: Multiple lytic lesions
General Findings
- Soft tissue calcification: Vascular calcification (arteries), periarticular deposits
- Osteopenia: Generalized bone density loss
- Pathological fractures: Vertebral compression, proximal femur
- Growth plate abnormalities: Rickets-like changes in children
- Chondrocalcinosis: Calcium pyrophosphate deposition
Advanced imaging:
- DEXA scan: Assesses bone mineral density (often osteopenic or osteoporotic)
- Lateral abdominal X-ray: Screens for aortic calcification
- Echocardiogram: Detects valvular calcification (aortic stenosis, mitral regurgitation)
- CT scan: Quantifies coronary artery calcium score (cardiovascular risk assessment)
Bone Biopsy (Gold Standard)
Indications:
- Diagnostic uncertainty regarding bone disease type (high vs low turnover)
- Unexplained bone pain or fractures
- Hypercalcemia with low PTH (suggestive of adynamic bone)
- Aluminum toxicity suspected (historical)
- Research purposes
Technique:
- Iliac crest biopsy with tetracycline double-labeling
- Undecalcified sections for histomorphometry
- Quantifies bone volume, turnover, mineralization
Histological classification:
- High-turnover disease (osteitis fibrosa cystica): Increased osteoid, osteoblast and osteoclast activity, marrow fibrosis
- Low-turnover disease (adynamic bone): Reduced osteoid, few osteoblasts/osteoclasts, no marrow fibrosis
- Mixed disease: Features of both high and low turnover
- Osteomalacia: Increased osteoid with prolonged mineralization lag time (rare in modern era)
Bone biopsy is rarely needed in clinical practice - treatment is guided by biochemistry (PTH, calcium, phosphate).
Differential Diagnosis
Secondary vs Primary vs Tertiary Hyperparathyroidism
| Feature | Secondary HPT (CKD) | Primary HPT | Tertiary HPT |
|---|---|---|---|
| Calcium | Low or normal | Elevated | Elevated |
| Phosphate | Elevated (CKD) | Low or normal | Variable |
| PTH | Elevated (appropriate response) | Elevated or inappropriately normal | Elevated (autonomous) |
| Renal function | Impaired (eGFR less than 60) | Normal or mildly impaired | Improved (post-transplant) or impaired |
| Mechanism | Compensatory to hypocalcemia | Autonomous PTH secretion (adenoma) | Autonomous after prolonged secondary |
| Treatment | Medical (vitamin D, binders, calcimimetics) | Parathyroidectomy | Parathyroidectomy |
Management Algorithm
📊 Management Algorithm
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Phosphate Management
Target: Phosphate less than 1.5 mmol/L
Dietary restriction:
- Low-phosphate diet: Limit dairy products, processed foods, cola drinks, nuts
- Protein restriction: 0.8-1.0 grams per kg per day (excessive restriction causes malnutrition)
- Dietitian consultation: Essential for education and compliance
Phosphate binders:
Phosphate Binder Options
| Type | Example | Dose | Advantages | Disadvantages |
|---|---|---|---|---|
| Calcium-based | Calcium carbonate | 1-3 grams elemental calcium per day with meals | Inexpensive, provides calcium | Vascular calcification risk, hypercalcemia |
| Non-calcium based | Sevelamer carbonate | 800-1600 mg three times daily with meals | No calcium load, reduces vascular calcification | Expensive, GI side effects |
| Non-calcium based | Lanthanum carbonate | 500-1000 mg three times daily with meals | Potent, low pill burden | Expensive, GI side effects, theoretical toxicity |
Dialysis optimization:
- Adequate dialysis removes phosphate (3-4 sessions per week, 4 hours per session)
- High-flux membranes improve phosphate clearance
- Longer or more frequent dialysis for refractory hyperphosphatemia
The primary goal is to control phosphate to reduce PTH drive and vascular calcification risk.
Management Algorithm
Surgical Management - Parathyroidectomy
Indications for Parathyroidectomy in CKD
Absolute indications:
- Refractory severe secondary hyperparathyroidism - PTH persistently greater than 800-1000 pg/mL despite maximal medical therapy (vitamin D, calcimimetics, phosphate control)
- Hypercalcemia with elevated PTH - calcium persistently greater than 2.65 mmol/L
- Calciphylaxis - calcific uremic arteriolopathy with severe secondary hyperparathyroidism
- Symptomatic bone disease - brown tumors, pathological fractures, intractable bone pain
Relative indications:
- Pruritus refractory to medical management (elevated calcium-phosphate product)
- Progressive vascular or soft tissue calcification
- Tertiary hyperparathyroidism post-renal transplant (autonomous PTH secretion with hypercalcemia)
Surgical Options
Parathyroidectomy Options in CKD
| Procedure | Technique | Advantages | Disadvantages |
|---|---|---|---|
| Subtotal parathyroidectomy | Remove 3.5 glands (leave half of one gland) | Preserves parathyroid function, avoids hypoparathyroidism | 10-15% recurrence rate |
| Total parathyroidectomy with autotransplantation | Remove all 4 glands, transplant 50-100 mg parathyroid tissue to forearm | Easy access for reoperation (forearm), lower recurrence | Risk of graft failure (5-10%), hypoparathyroidism |
| Total parathyroidectomy without autotransplantation | Remove all 4 glands, lifelong calcium and calcitriol | Lowest recurrence rate | Permanent hypoparathyroidism, lifelong supplementation |
Preoperative preparation:
- Optimize medical management - continue phosphate binders, vitamin D
- Imaging: Sestamibi scan and ultrasound to localize glands (less sensitive than primary HPT)
- Cardiovascular assessment - high perioperative risk in dialysis patients
- Informed consent - discuss hungry bone syndrome risk
Postoperative Management
Hungry bone syndrome:
- Occurs in 30-50% of patients after parathyroidectomy for severe secondary hyperparathyroidism
- Profound hypocalcemia and hypophosphatemia as demineralized skeleton avidly takes up minerals
- Risk factors: Preoperative PTH greater than 1000 pg/mL, large adenomas, elevated alkaline phosphatase
Treatment of hungry bone syndrome:
- Aggressive calcium replacement:
- Oral calcium 3-6 grams daily (divided doses)
- IV calcium gluconate if symptomatic (1-2 grams every 6 hours)
- Calcitriol: 0.5-2 micrograms daily
- Magnesium replacement: Often depleted, impairs PTH secretion
- Daily monitoring: Calcium, phosphate, magnesium for first week
- Gradual weaning: Over weeks to months as skeleton remineralizes
Long-term outcomes:
- PTH normalizes or becomes low - may develop adynamic bone disease
- Bone pain improves within weeks to months
- Brown tumors regress over 6-12 months
- Fracture risk decreases
- Pruritus resolves in 70-80%
Complications and Special Considerations
Calciphylaxis (Calcific Uremic Arteriolopathy)
Definition: Life-threatening arteriolar calcification causing painful skin necrosis
Incidence: 1-4% of dialysis patients per year
Risk factors:
- Female gender
- Obesity
- Warfarin use
- High calcium-phosphate product
- Diabetes mellitus
- Severe secondary hyperparathyroidism
Clinical presentation:
- Painful violaceous skin lesions progressing to necrosis
- Distribution: Lower legs, thighs, abdomen (areas with high adiposity)
- Livedo reticularis pattern
- Eschar formation with ulceration
Diagnosis:
- Skin biopsy: Calcification of dermal arterioles and adipose tissue (caution - may worsen necrosis)
- Imaging: Soft tissue calcification on plain X-rays
Treatment:
- Stop warfarin immediately - switch to heparin or direct oral anticoagulants
- Aggressive wound care - debridement, infection control
- Sodium thiosulfate - IV 25 grams three times weekly with dialysis (calcium chelator)
- Optimize phosphate and calcium control - avoid calcium-based binders
- Parathyroidectomy if severe secondary hyperparathyroidism
- Pain management - often requires opioids
Prognosis: 50% mortality (sepsis from infected wounds)
Fracture Management in CKD
Increased fracture risk:
- 2-4 times higher than age-matched general population
- Hip fracture most common, highest morbidity and mortality
- Vertebral compression fractures often asymptomatic
Perioperative considerations:
- Optimize medical management preoperatively - control PTH, calcium, phosphate
- High cardiovascular risk - careful anesthetic assessment
- Poor bone quality - soft bone (high-turnover disease) or brittle bone (low-turnover disease)
- Risk of hypercalcemia postoperatively - mobilization of immobilized calcium stores
Fracture fixation challenges:
- Soft bone in high-turnover disease - poor screw purchase, consider cement augmentation
- Brittle bone in low-turnover disease - increased periprosthetic fracture risk
- Delayed healing - impaired bone remodeling
- Higher infection risk - uremia impairs immune function
Postoperative management:
- Continue dialysis - optimize schedule around surgery
- Aggressive mobilization - reduce immobilization complications
- Thromboprophylaxis - balance bleeding risk (uremic platelet dysfunction) vs thrombosis risk
- Nutrition optimization - adequate protein (healing), avoid malnutrition
Postoperative Care
Post-Parathyroidectomy Care
Immediate Monitoring (24-72 hours):
- Calcium levels every 6 hours initially
- Watch for hungry bone syndrome (profound hypocalcemia)
- Symptoms: Perioral tingling, Chvostek sign, tetany
Hungry Bone Syndrome Management:
- Oral calcium 3-6 grams daily in divided doses
- IV calcium gluconate if symptomatic (1-2 grams every 6 hours)
- Calcitriol 0.5-2 micrograms daily
- Magnesium replacement often needed
Post-Fracture Care in CKD:
- Continue dialysis schedule around surgery
- Optimize nutrition (protein for healing)
- Early mobilization when stable
- Thromboprophylaxis (balance bleeding vs clot risk)
Outcomes
Treatment Outcomes
Medical Management:
- Phosphate control: Achievable in 60-70% with compliance
- PTH suppression: Target achieved in 40-50% with aggressive management
- Fracture prevention: Improved with optimized bone turnover
Parathyroidectomy Outcomes:
- Perioperative mortality: 2-3% (cardiovascular risk)
- PTH normalization: 85-95%
- Bone pain improvement: 70-80%
- Pruritus resolution: 70-80%
Fracture Outcomes in CKD:
- Hip fracture 1-year mortality: 30% (2x general population)
- Delayed healing common
- Fixation failure higher due to poor bone quality
Evidence Base and Key Studies
PTH Targets in CKD - KDIGO Guidelines
Kidney Disease: Improving Global Outcomes (KDIGO) • Kidney Int Suppl (2017)
Key Findings:
- Target PTH 2-9 times upper limit normal for CKD Stage 5 (dialysis) - NOT normal PTH
- Oversuppressing PTH to normal increases adynamic bone disease risk
- Maintain calcium 2.2-2.5 mmol/L, phosphate less than 1.5 mmol/L, calcium-phosphate product less than 4.4
- Bone biopsy gold standard for diagnosing bone disease type but rarely needed clinically
Clinical Implication: Target PTH elevation in CKD patients to maintain bone turnover. Normal PTH causes low-turnover bone disease (adynamic bone) which paradoxically increases fracture risk.
Limitation: Guidelines based on observational data and expert consensus; limited RCT evidence for specific PTH targets.
Fracture Risk in CKD
Nickolas TL, et al • J Bone Miner Res (2013)
Key Findings:
- Prospective cohort: fracture risk 2-4 times higher in CKD vs general population
- Risk increases with declining eGFR (CKD Stage 5 has 4-fold increase)
- Hip fracture most common and highest mortality (30% one-year mortality in dialysis patients)
- DEXA underestimates fracture risk in CKD - bone quality impaired despite normal density
Clinical Implication: CKD patients have significantly increased fracture risk that is not fully captured by bone density measurement. Consider clinical risk factors and biochemistry in fracture risk assessment.
Limitation: Observational study; heterogeneous CKD population with varying treatments and comorbidities.
Calcimimetics vs Vitamin D in Secondary HPT
Chertow GM, et al (EVOLVE Trial) • N Engl J Med (2012)
Key Findings:
- RCT of 3883 dialysis patients: cinacalcet vs placebo
- Cinacalcet reduced PTH effectively and reduced parathyroidectomy risk (HR 0.44)
- No significant reduction in primary composite outcome (death, MI, hospitalization for fracture)
- Increased hypocalcemia risk with cinacalcet
Clinical Implication: Calcimimetics effectively lower PTH and reduce need for parathyroidectomy in secondary hyperparathyroidism but uncertain benefit on hard outcomes (fracture, mortality).
Limitation: High dropout rate (50%); underpowered for fracture outcomes; industry-funded trial.
Parathyroidectomy Outcomes in CKD
Kestenbaum B, et al • Clin J Am Soc Nephrol (2004)
Key Findings:
- Retrospective cohort of 4558 dialysis patients undergoing parathyroidectomy
- Perioperative mortality 2-3% (high due to cardiovascular comorbidities)
- Hungry bone syndrome in 30-50% (profound hypocalcemia requiring aggressive replacement)
- Long-term: improved bone pain, pruritus resolution, reduced fracture risk
- Recurrence rate 10-15% (subtotal parathyroidectomy) vs 5% (total with autotransplantation)
Clinical Implication: Parathyroidectomy is effective for refractory secondary hyperparathyroidism but has significant perioperative risks. Reserve for medical management failures.
Limitation: Retrospective, single-center study; selection bias (sicker patients undergoing surgery); heterogeneous surgical techniques.
Exam Viva Scenarios
Practice these scenarios to excel in your viva examination
VIVA SCENARIOStandard
Scenario 1: Secondary Hyperparathyroidism Management
EXAMINER
"A 55-year-old man on hemodialysis for 8 years presents with diffuse bone pain. Blood tests show calcium 2.1 mmol/L, phosphate 2.2 mmol/L, PTH 650 pg/mL, alkaline phosphatase 320 U/L. He is taking calcium carbonate 1500 mg three times daily with meals as a phosphate binder. What is your assessment and management?"
EXCEPTIONAL ANSWER
This patient has **severe secondary hyperparathyroidism** with **high-turnover renal osteodystrophy** (osteitis fibrosa cystica). The key features are: (1) CKD Stage 5 on dialysis, (2) elevated PTH (650 pg/mL - above target of 2-9x upper limit normal which is 150-300 pg/mL for dialysis), (3) hyperphosphatemia (2.2 mmol/L, target less than 1.5 mmol/L), (4) elevated alkaline phosphatase (high bone turnover), (5) bone pain. My approach would be: First, **optimize phosphate control** - his current calcium carbonate dose may be inadequate or compliance poor. Options: (a) increase calcium carbonate dose, (b) switch to non-calcium phosphate binder (sevelamer or lanthanum) to reduce calcium load and vascular calcification risk, (c) reinforce dietary phosphate restriction (low dairy, processed foods), (d) optimize dialysis (adequate sessions, high-flux membranes). Second, **activated vitamin D therapy** to suppress PTH - start calcitriol 0.5-1 microgram daily or paricalcitol 2 micrograms with dialysis three times weekly. Monitor calcium weekly (risk of hypercalcemia). Third, if PTH remains elevated (greater than 800 pg/mL) despite these measures, add **calcimimetic (cinacalcet)** 30-60 mg daily, titrate based on PTH response. Fourth, **imaging workup** - hand X-rays for subperiosteal resorption, lateral spine X-ray for rugger jersey spine, assess for brown tumors. Fifth, if refractory to medical management (PTH persistently greater than 800-1000 despite maximal therapy), consider **parathyroidectomy**. I would counsel him that controlling PTH is essential to prevent fractures, brown tumors, vascular calcification, but target PTH is NOT normal - we aim for 2-9x upper limit normal to maintain bone turnover and avoid adynamic bone disease.
KEY POINTS TO SCORE
Recognize severe secondary hyperparathyroidism (PTH 650 pg/mL above target 150-300 for dialysis)
Optimize phosphate control FIRST - hyperphosphatemia drives PTH elevation
Activated vitamin D (calcitriol, paricalcitol) suppresses PTH directly
Calcimimetics (cinacalcet) for refractory cases, parathyroidectomy if medical management fails
COMMON TRAPS
✗Targeting normal PTH - causes adynamic bone disease (low turnover) which increases fracture risk
✗Not addressing hyperphosphatemia - phosphate retention is primary driver of secondary HPT
✗Excessive calcium-based phosphate binders - increases vascular calcification risk
✗Operating too early - parathyroidectomy reserved for refractory cases (PTH greater than 800-1000 despite maximal medical therapy)
LIKELY FOLLOW-UPS
"What is the difference between secondary and tertiary hyperparathyroidism?"
"Why is target PTH 2-9 times upper limit normal in dialysis patients?"
"What is hungry bone syndrome and how do you manage it?"
VIVA SCENARIOChallenging
Scenario 2: Rugger Jersey Spine and Brown Tumors
EXAMINER
"A 48-year-old woman on peritoneal dialysis for 10 years presents with a painful swelling of the jaw. X-rays show a lytic expansile lesion of the mandible. Spine X-rays show dense vertebral endplates (rugger jersey spine). Blood tests show calcium 2.8 mmol/L, PTH 1200 pg/mL. How do you assess and manage this patient?"
EXCEPTIONAL ANSWER
This is a case of **severe refractory secondary hyperparathyroidism** with **brown tumor of the jaw** and **rugger jersey spine** (classic radiographic findings of high-turnover renal osteodystrophy). The key features are: (1) very high PTH (1200 pg/mL - severely above target), (2) hypercalcemia (2.8 mmol/L - unusual in secondary HPT, suggests tertiary HPT or excessive vitamin D therapy), (3) brown tumor (osteoclastic giant cell lesion from severe PTH-driven bone resorption), (4) rugger jersey spine (dense vertebral endplates from subperiosteal bone formation). My approach would be: First, **confirm diagnosis** - the lytic jaw lesion is a brown tumor (benign, not malignant). Check additional biochemistry: phosphate, alkaline phosphatase (expect very high), 25-OH vitamin D. Second, **review current medical management** - is she on activated vitamin D (could explain hypercalcemia), phosphate binders, calcimimetics? If not on maximal therapy, optimize: (a) stop or reduce vitamin D if hypercalcemic, (b) switch to non-calcium phosphate binders, (c) start calcimimetics (cinacalcet) to lower PTH and calcium. Third, **assess for other complications** - skeletal survey for additional brown tumors, echocardiogram for valvular calcification, assess for vascular calcification. Fourth, given **very high PTH (1200 pg/mL), hypercalcemia, and symptomatic brown tumor**, this patient is a candidate for **parathyroidectomy**. Options: subtotal parathyroidectomy or total with autotransplantation to forearm. Fifth, **preoperative preparation** - imaging with sestamibi and ultrasound (may localize hyperplastic glands), cardiovascular assessment (high perioperative risk), counsel about hungry bone syndrome (very high risk given PTH 1200, elevated ALP). Postoperatively, brown tumors should regress over 6-12 months without specific jaw surgery.
KEY POINTS TO SCORE
Brown tumor is benign osteoclastic lesion from severe secondary HPT - regresses after parathyroidectomy
Rugger jersey spine (dense vertebral endplates) is pathognomonic for renal osteodystrophy
Hypercalcemia in CKD patient suggests tertiary HPT (autonomous PTH secretion) or excessive vitamin D
Parathyroidectomy indicated for refractory secondary HPT (PTH greater than 1000, symptomatic brown tumors, hypercalcemia)
COMMON TRAPS
✗Misdiagnosing brown tumor as malignancy (metastasis, myeloma) - check calcium and PTH to distinguish
✗Operating on jaw lesion before treating underlying HPT - brown tumors regress after parathyroidectomy
✗Not recognizing rugger jersey spine as renal osteodystrophy (specific finding)
✗Underestimating hungry bone syndrome risk - PTH 1200 pg/mL means very high risk of profound hypocalcemia post-parathyroidectomy
LIKELY FOLLOW-UPS
"How do you differentiate a brown tumor from a giant cell tumor?"
"What is the mechanism of rugger jersey spine formation?"
"Describe the surgical options for parathyroidectomy in CKD."
VIVA SCENARIOCritical
Scenario 3: Calciphylaxis Presentation
EXAMINER
"A 62-year-old obese diabetic woman on hemodialysis develops painful violaceous skin lesions on her thighs with central necrosis. She is on warfarin for atrial fibrillation. Blood tests show calcium 2.6 mmol/L, phosphate 2.0 mmol/L, PTH 420 pg/mL. She is taking calcium carbonate as a phosphate binder. What is your diagnosis and management?"
EXCEPTIONAL ANSWER
This is **calciphylaxis** (calcific uremic arteriolopathy), a life-threatening complication of CKD with 50% mortality. The key features are: (1) painful violaceous skin lesions progressing to necrosis (classic presentation), (2) high-risk patient (obese, diabetic, on dialysis, warfarin use), (3) elevated calcium-phosphate product (calcium 2.6 x phosphate 2.0 = 5.2 mmol squared per L squared, above target less than 4.4), (4) secondary hyperparathyroidism (PTH 420). My approach would be: First, **confirm diagnosis** - clinical diagnosis based on characteristic skin lesions. Skin biopsy shows calcification of dermal arterioles and adipose tissue but may worsen necrosis so use caution. X-rays may show soft tissue calcification. Second, **immediate management**: (a) **stop warfarin immediately** - major risk factor, switch to heparin or direct oral anticoagulant, (b) **aggressive wound care** - debridement of necrotic tissue, infection control with antibiotics if infected, pain management (often requires opioids), (c) **IV sodium thiosulfate** 25 grams three times weekly with dialysis (calcium chelator, improves outcomes in case series). Third, **optimize mineral metabolism**: (a) reduce calcium load - **stop calcium carbonate**, switch to non-calcium phosphate binder (sevelamer), (b) aggressive phosphate control to reduce calcium-phosphate product, (c) reduce or discontinue vitamin D if hypercalcemia. Fourth, consider **parathyroidectomy** if severe secondary hyperparathyroidism contributing (PTH 420 is moderately elevated - may benefit). Fifth, **multidisciplinary care** - involve nephrology, dermatology, wound care, vascular surgery if needed. I would counsel that calciphylaxis has 50% mortality from sepsis and wound complications. Prognosis depends on early recognition, aggressive wound care, and correction of metabolic abnormalities.
KEY POINTS TO SCORE
Calciphylaxis = painful violaceous skin necrosis from arteriolar calcification (50% mortality)
Risk factors: obesity, diabetes, warfarin, high calcium-phosphate product, female gender
Stop warfarin immediately - major modifiable risk factor
Treatment: sodium thiosulfate, aggressive wound care, optimize mineral metabolism, avoid calcium-based binders
COMMON TRAPS
✗Delaying diagnosis - calciphylaxis is life-threatening, requires urgent treatment
✗Not stopping warfarin - major precipitant, switch to alternative anticoagulation
✗Continuing calcium-based phosphate binders - worsens vascular calcification
✗Inadequate pain management - lesions are excruciatingly painful, often require opioids
LIKELY FOLLOW-UPS
"What is the pathophysiology of calciphylaxis?"
"What is the mechanism of sodium thiosulfate in calciphylaxis treatment?"
"How does warfarin contribute to calciphylaxis risk?"
MCQ Practice Points
PTH Target Question
Q: What is the target PTH for a patient on hemodialysis (CKD Stage 5)?
A: 2-9 times the upper limit of normal, which translates to approximately 150-300 pg/mL (normal PTH is 10-65 pg/mL). This elevated PTH target maintains adequate bone turnover. Suppressing PTH to normal causes adynamic bone disease (low turnover) which paradoxically increases fracture risk and impairs bone healing.
Rugger Jersey Spine Question
Q: What is rugger jersey spine and what does it indicate?
A: Rugger jersey spine is dense vertebral endplates (sandwich vertebrae) creating horizontal bands on lateral spine X-ray, resembling a rugby jersey. It results from subperiosteal bone formation in high-turnover renal osteodystrophy (secondary hyperparathyroidism). Pathognomonic for CKD-mineral bone disorder.
Calciphylaxis Question
Q: A dialysis patient develops painful violaceous skin lesions with necrosis on the thighs. What is the diagnosis and immediate management?
A: Calciphylaxis (calcific uremic arteriolopathy). Life-threatening with 50% mortality. Immediate management: (1) stop warfarin (major risk factor), (2) aggressive wound care (debridement, infection control), (3) IV sodium thiosulfate 25 grams three times weekly with dialysis, (4) stop calcium-based phosphate binders, (5) optimize calcium-phosphate product to less than 4.4 mmol squared per L squared.
Secondary vs Tertiary HPT Question
Q: How do you distinguish secondary from tertiary hyperparathyroidism?
A: Secondary HPT: Low or normal calcium with elevated PTH (appropriate compensatory response to hypocalcemia in CKD). Tertiary HPT: Elevated calcium with elevated PTH (autonomous PTH secretion after prolonged secondary HPT, typically post-renal transplant). Treatment differs - secondary HPT is medical (vitamin D, phosphate binders, calcimimetics), tertiary HPT requires parathyroidectomy.
Australian Context
Australian Practice Considerations
PBS Medications:
- Sevelamer carbonate: PBS listed for hyperphosphatemia in dialysis
- Lanthanum carbonate: PBS listed for hyperphosphatemia
- Calcitriol: PBS listed for secondary hyperparathyroidism
- Cinacalcet: PBS listed for refractory secondary HPT
ANZDATA Registry:
- Australia and New Zealand Dialysis and Transplant Registry
- Tracks outcomes for dialysis and transplant patients
- Provides Australian-specific fracture and mortality data
Dialysis Access:
- Hemodialysis: Major metropolitan and regional centers
- Peritoneal dialysis: Home-based option
- Renal transplant: Major tertiary centers
RENAL OSTEODYSTROPHY
High-Yield Exam Summary
Key Pathophysiology
- •CKD causes phosphate retention (reduced renal excretion) and reduced calcitriol production (impaired 1-alpha hydroxylation)
- •Hypocalcemia and hyperphosphatemia drive secondary hyperparathyroidism (compensatory)
- •PTH causes bone resorption (high-turnover disease - osteitis fibrosa cystica)
- •Oversuppression of PTH causes low-turnover disease (adynamic bone) which increases fracture risk
Spectrum of Bone Disease
- •Osteitis fibrosa cystica: High-turnover from severe secondary HPT (brown tumors, subperiosteal resorption)
- •Adynamic bone disease: Low-turnover from oversuppressed PTH (increased fracture risk)
- •Mixed disease: Most common, features of both high and low turnover
- •Bone biopsy is gold standard but rarely needed (treat based on biochemistry)
Target Biochemistry
- •PTH: 2-9x upper limit normal for CKD stage (150-300 pg/mL for dialysis, NOT normal)
- •Calcium: 2.2-2.5 mmol/L (avoid hypercalcemia - vascular calcification risk)
- •Phosphate: less than 1.5 mmol/L (phosphate binders plus dietary restriction)
- •Ca x PO4 product: less than 4.4 mmol squared per L squared (prevent vascular calcification)
- •25-OH vitamin D: greater than 75 nmol/L (substrate for calcitriol production)
Radiographic Features
- •Rugger jersey spine: Dense vertebral endplates (sandwich vertebrae) - pathognomonic
- •Subperiosteal resorption: Radial side of middle phalanges (hand X-ray)
- •Salt and pepper skull: Loss of skull trabeculation
- •Brown tumors: Lytic lesions from severe secondary HPT (jaw, ribs, pelvis)
- •Vascular calcification: Arteries, heart valves, soft tissues
Medical Management
- •Phosphate control: Binders (calcium carbonate or sevelamer) plus dietary restriction
- •Vitamin D: Replete 25-OH vitamin D, then activated vitamin D (calcitriol, paricalcitol) to suppress PTH
- •Calcimimetics: Cinacalcet for refractory secondary HPT (PTH greater than 300-800 despite vitamin D)
- •Calcium management: Target 2.2-2.5 mmol/L, avoid excess (vascular calcification risk)
- •Dialysis optimization: Adequate sessions remove phosphate, maintain mineral balance
Parathyroidectomy Indications
- •Refractory secondary HPT: PTH persistently greater than 800-1000 despite maximal medical therapy
- •Hypercalcemia with elevated PTH (tertiary HPT)
- •Symptomatic bone disease (brown tumors, pathological fractures, intractable pain)
- •Calciphylaxis with severe secondary HPT
- •Options: Subtotal (3.5 glands) or total with autotransplantation to forearm
Complications
- •Hungry bone syndrome: Profound hypocalcemia post-parathyroidectomy (30-50% risk), requires aggressive calcium replacement
- •Calciphylaxis: Painful skin necrosis from arteriolar calcification (50% mortality), stop warfarin, sodium thiosulfate
- •Fracture risk: 2-4x higher than general population, poor bone quality (soft or brittle)
- •Vascular calcification: Coronary arteries, heart valves, peripheral vessels (increased cardiovascular mortality)