CKD MBD; make it easy

CKD-MBD; Make it Easy
By
Shady Yousef Gayed
MBBCh, MSc, MD
Honorary Lecturer of Internal
Medicine and Nephrology
Assiut University Hospitals

DEFINITIONS
In 2006, (KDIGO) recommended the use of the term
chronic kidney disease-mineral and bone disorder (CKD-
MBD) in stead of "renal osteodystrophy" to describe a
systemic disorder that manifested by either one or a
combination of the following:
●Abnormalities of calcium, phosphorus,
parathyroid hormone (PTH), fibroblast growth factor 23
(FGF23), and vitamin D metabolism
●Abnormalities in bone turnover, mineralization,
volume, linear growth, or strength
●Extraskeletal calcification
KDIGO CKD-MBD guidelines, Kidney Int Suppl. 2009;(113):S1-130

DEFINITIONS
• The work group recommended that the traditional
term "renal osteodystrophy" be exclusively used to
define alterations in bone morphology associated with
CKD and stated that definitive diagnosis of renal
osteodystrophy can only be made by bone biopsy
KDIGO CKD-MBD guidelines, Kidney Int Suppl. 2009;(113):S1-130

Mineral &
hormonal
disruption
Bone disease
Extra-skeletral
calcification
Pathogenesis
of

Mineral & hormonal disruption
pathogenesis
Mineral & hormonal abnormalities includes:
Hypocalcemia and calcium-sensing receptor.
Phosphate retention and Hyperphosphatemia.
Decreased calcitriol activity.
Fibroblast growth factor-23.
Secondary hyperparathyroidism.
Tertiary hyperparathyroidism.
Skeletal resistance to PTH.

Hypocalcemia
Decreased
Calcitrol (1,25
dihydroxyvit.D)
Concentration

Hypocalcemia
Decreased
Calcitrol (1,25
dihydroxyvit.D)
Concentration
Resistance
to calcemic
effect of
PTH on
bone

Hypocalcemia
Decreased
Calcitrol (1,25
dihydroxyvit.D)
Concentration
Resistance
to calcemic
effect of
PTH on
bone
Hyperparathyroidism

With progressive CKD, phosphate is retained, at
least, transiently, by the failing kidney. However,
hyperphosphatemia usually does not become
evident before CKD stage 4.
Until then, compensatory hyperparathyroidism
and increases in circulating FGF-23 result in
increased phosphaturia, maintaining serum
phosphate levels in the normal range
Gutierrez O, Isakova T, Rhee E, et al. Fibroblast growth factor-23 mitigates hyperphosphatemia
but accentuates calcitriol deficiency in chronic kidney disease. J Am Soc Nephrol. 005;16:2205–
2215.
Phosphate retention andHyperphosphatemia

Comprehensive Clinical Nephrology, SIXTH EDITION, 2019.

Direct effect

Decreased
Calcitrol activity
Early stage
GFR <70 ml/min
↓GFR
↑
Phosphate

Decreased
Calcitrol activity
Early stage
GFR <70 ml/min
↑ FGF-23
↓GFR
↑
Phosphate
Gutierrez, O., Isakova, T., Rhee, E., Shah, A., Holmes, J., Collerone, G., . . . Wolf, M. (2005). Fibroblast growth factor-23 mitigates
hyperphosphatemia but accentuates calcitriol deficiency in chronic kidney disease. J Am Soc Nephrol, 16(7), 2205-2215.

Decreased
Calcitrol activity
Early stage
GFR <70 ml/min
Advanced CKD
Hyperphos-
phatemia
Loss of
functioning
renal mass
&↓GFR
↑Carboxyl-
terminal
parathyroid
hormone
↑ FGF-23
↓GFR
↑
Phosphate
Gutierrez, O., Isakova, T., Rhee, E., Shah, A., Holmes, J., Collerone, G., . . . Wolf, M. (2005). Fibroblast growth factor-23 mitigates
hyperphosphatemia but accentuates calcitriol deficiency in chronic kidney disease. J Am Soc Nephrol, 16(7), 2205-2215.

Fibroblast growth factor-23
• FGF-23 is a circulating peptide that plays a key role in
the control of serum phosphate concentrations.
• FGF-23 is secreted by bone osteocytes and osteoblasts
in response to calcitriol, increased dietary phosphate
load, PTH, and calcium.
• Klotho, a transmembrane protein produced by
osteocytes, is required for FGF-23 receptor activation.
• FGF-23's primary function is to maintain normal serum
phosphate concentration by reducing renal phosphate
reabsorption and by reducing intestinal phosphate
absorption through decreased calcitriol production.
Miyamoto K, Ito M, Tatsumi S, et al. New aspect of renal phosphate reabsorption: the type IIc
sodium-dependent phosphate transporter. Am J Nephrol 2007; 27:503

Fibroblast growth factor-23
• In renal proximal tubular cells, FGF-23 binds to the FGF
receptor (FGFR) and its coreceptor, klotho, causing inhibition
of the expression of the Na/Pi IIa cotransporter.
• FGF-23 also suppresses PTH secretion by the parathyroid
gland. However, among CKD patients, the presence of high
PTH concentrations, despite high FGF-23 concentrations,
suggests that the parathyroid is relatively resistant to the
elevated concentrations of FGF-23 in uremia.
• This may be related to the markedly decreased expression
of FGFR 1 and klotho protein in the hyperplastic parathyroid
gland.
Komaba H, Goto S, Fujii H, et al. Depressed expression of Klotho and FGF receptor 1 in
hyperplastic parathyroid glands from uremic patients. Kidney Int 2010; 77:232.

Kovesdy, C. P., & Quarles, L. D. (2013). Fibroblast growth factor-23: what we know, what we
don't know, and what we need to know. Nephrol Dial Transplant, 28(9), 2228-2236.
FGF23 OUTCOMES

Mineral metabolism abnormalities
Secondary hyperparathyroidism is a major feature of CKD-
MBD. Secondary hyperparathyroidism begins early in the
course of CKD (particularly to eGFR <60 mL/min/1.73 m2),
and its prevalence increases as kidney function declines.
Secondary hyperparathyroidism occurs in response to a
series of abnormalities that initiate and maintain increased
parathyroid hormone (PTH) secretion.
Cunningham, J., Locatelli, F., & Rodriguez, M. (2011). Secondary hyperparathyroidism:
pathogenesis, disease progression, and therapeutic options. Clin J Am Soc Nephrol, 6(4), 913-921.

Mineral metabolism abnormalities
The main abnormalities that contribute to the pathogenesis of
secondary hyperparathyroidism are:
●Phosphate retention.
●Decreased free ionized calcium concentration.
●Decreased 1,25-dihydroxyvitamin D (calcitriol) concentration.
●Increased fibroblast growth factor 23 (FGF23) concentration.
●The reduced expression of vitamin D receptors (VDRs),
calcium-sensing receptors (CaSRs), fibroblast growth factor
receptors, and klotho in the parathyroid glands.

Prolonged &persistent stimulation
of parathyroid gland by
Nodular
hyperplasia
↓ expression of CasRs
and VDRs
No response to ↑
Ca level
Pathogenesis of tertiary hyperparathyroidism
Hyperparathyroism + Hypercalcemia
Autonomous PTH
secretion
 Hypocalcemia.
 ↓ Calcitrol.
 ↑ Phosphate

Pathogenesis
of Skeletal
resistance
to PTH
Comprehensive Clinical Nephrology, SIXTH EDITION,
2019.

Down-
regulation of
the PTH
receptor
↑Carboxylase-
terminal PTH
fragments
Phosphate
retention
↓ 25 (OH)D3
Pathogenesis
of Skeletal
resistance
to PTH
Comprehensive Clinical Nephrology, SIXTH EDITION,
2019.

KDIGO recommends that three parameters be used to
assess bone pathology. These parameters include bone
turnover, mineralization, and volume (TMV system). Any
combination of parameters may be used to describe a
given sample. The TMV system of classification of renal
osteodystrophy serves to emphasize the contributions of
mineralization and volume, as well as turnover, to bone
quality.
KDIGO CKD-MBD guidelines, Kidney Int Suppl. 2017;7:1–59
Renal Osteodystrophy pathogenesis

TMV characteristics of the major CKD-related bone
diseases are as follows:
●Osteitis fibrosa
●Adynamic bone
●Osteomalacia
●Mixed uremic osteodystrophy
● Dialysis-related amyloidosis
Renal Osteodystrophy pathogenesis
KDIGO CKD-MBD guidelines, Kidney Int Suppl. 2017;7:1–59

 Secondary or tertiary HPTH.
 High turnover bone disease.
 Characterized by Cortical bone loss, increased
osteoclast and osteoblast activity, endo-osteal fibrosis.
 Biochemically: high Ca, PTH, Pi, AP and osteocalcin.
1- Osteitis fibrosa cystica
Malluche et al, Nat Rev Nephrol. 2010; 6: 32-40

Barreto, F. d. C., Costa, C. R. V. d., Reis, L. M. d., & Custódio, M. R. (2018). Bone biopsy in
nephrology practice. Brazilian Journal of Nephrology, 40, 366-374.
A) Histological characteristics of osteitis fibrosa, showing an increased bone
formation represented by osteoid surface (O), osteoblast number (Obl),
resorption, and osteoclast number (Ocl). There is an extensive area of marrow
fibrosis (MF). Toluidine Blue (x100). MB: mineralized bone; BM: bone marrow.

 Over suppression of PTH.
 Patients at risk, elderly, peritoneal dialysis, ca based
binders, over-suppressed PTH.
 Low cellular activity (few osteoblasts and osteoclasts)
with thin osteoid.
 Loss of cancellous bone.
 High cardiovascular and soft tissue calcification and
high mortality.
 Biochemically: High Ca, low PTH and AP.
2-Adynaemic bone disease
Malluche et al, Nat Rev Nephrol. 2010; 6: 32-40

G) Histological characteristics observed in adynamic bone disease, showing
decreased bone formation and resorption and no marrow fibrosis (MF). Toluidine
blue (x40).

 low bone turnover in combination with defective
mineralization.
 Risk factors: hypophosphataemia, low vitamin D, and
aluminum intoxication (lack of water purification in
the past or excessive aluminum-based binders).
 Wide un-menarlized osteoid, absent/few osteoblast
and osteoclasts.
 Biochemically: low phosphate, Ca, and normal to high
PTH and AP.
3-Osteomalcia
Moorthi, R. N., & Moe, S. M. (2011). CKD-mineral and bone disorder: core curriculum 2011. Am J Kidney
Dis, 58(6), 1022-1036.

E) Histological characteristics of Osteomalacia, showing a dramatic increase of
bone formation represented by an extensive osteoid surface (O) and thickness
(arrow). Toluidine blue (x100).

 Mixed uremic osteodystrophy is characterized by
either high or low bone turnover and by abnormal
mineralization.
4-Mixed uremic osteodystrophy
Moorthi, R. N., & Moe, S. M. (2011). CKD-mineral and bone disorder: core curriculum 2011. Am J Kidney
Dis, 58(6), 1022-1036.
5-Dialysis-related amyloidosis
 occurs in patients on long-term dialysis and presents
as bone cysts, which result from beta2-microglobulin-
associated amyloid deposits.

RISK FACTORS for VC include the following:
●Increasing age
●Dialysis vintage for those patients on dialysis
●Hyperphosphatemia
●Positive net calcium and phosphate balance and
calcium intake
●High calcium-phosphate product
●Vitamin D therapy
●Diabetes
●Dyslipidemia
●Oral inhibitors of vitamin K (eg, Warfarin)
Extra-skeletral calcification pathogenesis

 Extraskeletal calcification is common in patients
with CKD, particularly those on dialysis, and it
contributes to cardiovascular mortality.
 Aggravated by persistent elevation of the calcium-
phosphate product.
 Most commonly, vascular calcifications are seen,
but calcifications may occur in other sites, such as
the lung, myocardium, and periarticular areas.
Extra-skeletral calcification pathogenesis

Calcific uremic arteriolopathy
(Calciphylaxis)
Calcific uremic arteriolopathy is a rare and serious
disorder characterized by systemic medial
Calcification of the arterioles that leads to ischemia
and subcutaneous necrosis.

Clinical Manifestations
• Most with CKD and mildly elevated PTH are
asymptomatic
• When present classified as either
1. Musculoskeletal
2. Extra-skeletal

1. Musculoskeletal
Bone pain: Nonspecific aches and pains are common, occur in
the lower back, hips, and legs, and are aggravated by weight
bearing. Acute, localized bone pain can occur and may be
suggestive of acute arthritis. Pain around joints may be caused
by acute periarthritis, which is associated with periarticular
deposition of calcium phosphate.
Muscle pain & weakness.
Tendon rupture.
Avascular necrosis.
Carpal tunnel syndrome.
Fractures: most clinically significant is fracture neck of femur
seen in CKD 5 (associated with increase mortality).

2. Extra-skeletal
CVD accounts for around half of all mortalities of dialysis
patients.
Coronary artery and vascular calcifications occur
frequently in CKD 5 (and increase each year on dialysis).
Calcifications may occur in other sites, such as the lung,
myocardium, and periarticular areas.
Calcific uremic arteriolopathy(Calciphylaxis).

DIAGNOSIS OF CKD-MBD: biochemical
abnormalities
KDIGO 2017 Clinical Practice Guideline Update for the Diagnosis, Evaluation, Prevention, and
Treatment of CKD-MBD. Kidney Int Suppl. 2017;7:1–59.

Laboratory Target levels
Calcium and phosphorus levels
• For patients with stage 3 to 5D CKD, the KDIGO working
group suggest:
● Maintaining serum calcium and phosphorus in the normal
range.
● Evaluating individual values of serum calcium and
phosphorus together, rather than the calcium-phosphorus
product.
Parathyroid hormone levels
• In CKD 5D it is recommended to maintain PTH level in the
range of approximately 2-9 times the upper limit of normal
for the assay.

DIAGNOSIS OF CKD-MBD: Bone

DIAGNOSIS OF CKD-MBD: vascular
calcification

Radiological signs of CKD-MBD
• Routine x-ray examination of the skeleton is relatively
insensitive for the diagnosis of renal osteodystrophy,
and x-ray films can appear virtually normal in patients
with severe histologic evidence of renal osteodystrophy.
• Subperiosteal erosions are often present in severe
secondary hyperparathyroidism.
• Osteosclerosis of the vertebrae is responsible for the
“rugger-jersey” appearance of the spine.
• rarely, brown tumors, focal collections of giant cells and
typical of severe hyperparathyroidism, are seen as well
demarcated radiolucent zones in long bones, clavicles,
and digits.

Radiological signs of CKD-MBD
Subperiosteal erosions rugger-jersey spine
brown tumors

Advantages and limitations of different methods for
the evaluation of bone tissue
Advantages Limitations
Serum biomarkers of bone
remodelling:
ALP
Bone ALP
PTH
*Low cost.
*Availability.
*Non-invasive.
*Provide guidance for the
treatment of CKD-MBD in
the daily clinical practice
*Kidney function may
interfere on levels.
*Low to moderate accuracy
to predict the type of ROD.
*Lack of information on
bone density.
DXA *Non-invasive.
*Low cost.
*Availability.
*Prediction of bone
fracture.
*Lack of differentiation
between cortical and
trabecular bone
*Lack of information on
bone mineralization,
turnover and
microarchitecture

High resolution–
quantitative
peripheral
computerized
tomography
*Non-invasive.
*High definition image.
*Assesses separately cortical and
trabecular bone.
*Assesses bone density and
microarchitecture.
*Estimation of bone strength.
*High cost, radiation
exposure, low availability.
*Limited to peripheral sites.
*Lack of information on bone
mineralization and turnover.
*Lack of standardization.
*Few studies in CKD patients.
MRI *Non-invasive, no radiation.
*Assesses separately cortical and
trabecular bone.
*Can produce 3D images.
*Shows other aspects of bone
physiology not assessed by other
techniques, such as marrow fat
content, perfusion and molecular
diffusion.
*High cost.
*Low availability.
*Lack of information on bone
*mineralization and turnover.
*Few studies in CKD patients.

Bone biopsy +
histomorphometry
*High specificity and
sensitivity to diagnose bone
diseases, including ROD.
*Assesses separately cortical
and trabecular bone.
*Information on bone
mineralization and turnover.
*Invasive, painful, costy.
*Few specialized centres on
this technique.
*Does not evaluate bone
density.
*No data on fracture risk
prediction.

1) Dietary phosphate restriction
• Among patients with PTH or serum phosphate levels
greater than target levels, it is suggested to restrict
dietary phosphate intake to 900 mg/day.
• Dietary phosphorus restriction can keep phosphorus
normal in CKD 3-5 and act as an adjunct to other
methods in dialysis patients.
• Dietary phosphorus should be derived from sources of
high biologic value, such as meats and eggs.
Phosphorus from food additives and fast foods should
also be estimated and restricted.

2) Phosphate binders
Choice of agent:
●Hypocalcemic patients: we generally use calcium-
containing phosphate binders. Hypocalcemic patients are
less likely to become hypercalcemic with calcium-
containing binders.
●Normocalcemic patients: we generally use calcium-
containing phosphate binders for normocalcemic patients
who have no evidence of vascular calcification or adynamic
bone disease.
●Hypercalcemic patients: we generally use non-calcium-
containing phosphate binders for hypercalcemic patients.
●Patients with adynamic bone disease or vascular
calcification: we generally use non-calcium-containing
phosphate binders for these patients

Overwiew of phosphate binders
Class of phosphate binder Advantages Disadvantages
Al-based
(Al hydroxide)
Effective across wide pH
range, inexpensive.
Absorption of Al can lead to
long-term toxicity resulting in
neurological damage and
possible death.
Ca-based
(Ca acetate, Ca carbonate)
Effective, inexpensive, well
tolerated, well established,
widely available
Likely to increase
hypercalcaemia, and risk of
arterial calcification, high tablet
burden.
Non Ca-based
Sevelamer HCL
Sevelamer carbonate
Lanthanum carbonate
Metal-free, low toxicity,
lowers lipids and arterial
calcification – does not
affect Ca
Acidosis due to HCl.
expensive.
May require ca supply in cases
of hypocalcemia.
GI side effects.

3) Vitamin D, calcitriol, and vitamin D
analogs:
• Vitamin D includes both vitamin D2 (ergocalciferol) and
vitamin D3 (cholecalciferol).
• Vitamin D derivatives include:
1) the naturally occurring vitamin D metabolite, calcitriol
(1,25-dihydroxycholecalciferol).
2) synthetic vitamin D analogs such as doxercalciferol,
paricalcitol, alfacalcidol, falecalcitriol, and 22-xacalcitriol (or
maxacalcitol [1,25 dihydroxy-22-oxavitamin D3]).

Management of Vitamin D Deficiency
In CKD stages 3-5D, vitamin D deficiency and
insufficiency suggest to be corrected using
treatment strategies recommended for the general
population.
Supplementation with either ergocalciferol or
cholecalciferol is recommended, but the optimal
treatment regimen is not known.

 Most dialysis patients with increased plasma iPTH evels
(>300 pg/mL) require treatment with calcitriol or vitamin
D analogs.
 Because calcitriol increases gastrointestinal absorption of
calcium and phosphate, more selective vitamin D analogs
have been developed that may reduce the risk of
hypercalcemia and hyperphosphatemia.
 The continued up-titration with active vitamin D to
supraphysiologic levels, if necessary to suppress PTH, is
often successful in lowering PTH, but frequently achieves
this one goal at the expense of hypercalcemia and
hyperphosphatemia.
Calcitriol and synthetic vitamin D analogs

Contraindications
1- Calcitriol or synthetic vitamin D analogs should not be given
until the serum phosphorus concentration has been controlled
(<5.5 mg/dL) and the serum calcium is <9.5 mg/dL.
2- Low plasma PTH concentration, possibly <150 pg/mL, because of
the association with adynamic bone disease.
• Empiric observations suggest that somewhat higher than
normal PTH levels are required for normal bone formation
rates in patients with kidney disease, presumably due to the
end-organ resistance to PTH observed in uremia.
Calcitriol and synthetic vitamin D analogs

4) Calcimimetics
(Cinacalcet)
 Calcimimetics are agents that increase the sensitivity of
the calcium-sensing receptor (CaSR) in the parathyroid
gland to calcium, regulating PTH secretion and the
gland hyperplasia.
 Studies have found that the addition of cinacalcet to
current treatment regimens increases the percentage of
patients who are able to attain PTH, calcium, and
phosphate target levels.

4) Calcimimetics
(Cinacalcet)
• Dose:
Cinacalcet is initiated at a dose of 30 mg/day, with
stepwise increments to 60, 90, and 180 mg/day. The dose
can be increased every four weeks until goals are
achieved.
• Contraindications:
Cinacalcet should not be started if serum calcium is <8.4
mg/dL. Frequent monitoring of plasma calcium and PTH
levels is needed.

Indications of parathyroidectomy

Adynamic Bone Disease treatment
• The initial approach to treatment of adynamic bone
disease is to allow PTH secretion to rise.
• This can be achieved by:
1. decreasing the doses of calcium-based phosphate
binders,
2. using non-calcium-based phosphate binders;
3. decreasing or stopping active vitamin D analogs; and,
4. for patients on dialysis, possibly by using a low dialysate
calcium concentration (1.25-1.5 mmol/l).

CKD MBD; make it easy

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