Medicine Marrow Pg No 885-894 (Endocrinology)
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Questions and Answers

Which clinical feature is NOT associated with hypophosphatemia?

  • Rhabdomyolysis
  • Increased insulin sensitivity (correct)
  • Cardiomyopathy
  • Growth retardation

    • Severe vitamin D deficiency can lead to hypophosphatemia.

    True

    What is the most common metabolic abnormality seen in refeeding syndrome?

    Hypophosphatemia

    Patients with hypophosphatemia should avoid foods rich in __________.

    <p>phosphate</p> Signup and view all the answers

    Match the causes of hypophosphatemia with their descriptions:

    <p>Nutritional vitamin D dependent rickets = Decreased dietary intake of phosphate Sepsis = Decreased calcium leading to decreased phosphate Heat stroke = Resulting in tissue and electrolyte imbalances Refeeding syndrome = Common metabolic abnormality causing low phosphate levels</p> Signup and view all the answers

    Which of the following is the most common cause of excess phosphorus intake?

    <p>Phosphate-containing enema</p> Signup and view all the answers

    Hyperphosphatemia primarily causes symptoms similar to hypercalcemia.

    <p>False</p> Signup and view all the answers

    Name one condition that can lead to the redistribution of phosphorus from cell to blood.

    <p>Rhabdomyolysis</p> Signup and view all the answers

    Familial tumoral calcinosis is inherited in an ______ manner.

    <p>autosomal recessive</p> Signup and view all the answers

    Match the following phosphate binders with their respective examples:

    <p>Phosphate binder = Sucroferric oxyhydroxide</p> Signup and view all the answers

    Which condition is associated with x-linked inheritance related to hypophosphatemic rickets?

    <p>PHEX gene mutation</p> Signup and view all the answers

    Autosomal dominant conditions related to phosphorus metabolism lead to an increase in FGF 23.

    <p>True</p> Signup and view all the answers

    What is the daily requirement of phosphorus for an individual?

    <p>2 g</p> Signup and view all the answers

    In severe hypophosphatemia, phosphorus is administered via _____ at a dosage of 10 mg/kg over 12 hours.

    <p>IV</p> Signup and view all the answers

    Match the following gene mutations with their outcomes:

    <p>PHEX gene = ↓ cleavage of FGF 23 DMP mutation = ↓ FGF 23 FGF 23 mutation = ↑ FGF 23 Gain of function mutation of FGF 23 = Tumor induced osteomalacia</p> Signup and view all the answers

    What happens during the end stages of Chronic Kidney Disease regarding FGF-23?

    <p>FGF-23 is inactivated</p> Signup and view all the answers

    In Fanconi syndrome, phosphate depletion can lead to severe rickets.

    <p>True</p> Signup and view all the answers

    Which cotransporter is primarily responsible for the reabsorption of phosphorus in the proximal convoluted tubule?

    <p>Na⁺-P cotransporter</p> Signup and view all the answers

    In Chronic Kidney Disease, increased levels of parathyroid hormone (PTH) lead to an increase in ______.

    <p>calcium</p> Signup and view all the answers

    Match the conditions with their corresponding effects on phosphorus:

    <p>Fanconi syndrome = Severe phosphate depletion Chronic Kidney Disease (Early stages) = Phosphaturia with normal serum phosphorus Chronic Kidney Disease (End stages) = Increased serum phosphorus Increased PTH = Increased calcium</p> Signup and view all the answers

    What is the range for hypophosphatemia in mg/dL?

    <p>1-2.5</p> Signup and view all the answers

    Inorganic phosphorus is primarily extracellular and mainly used to measure serum phosphorus.

    <p>True</p> Signup and view all the answers

    Where in the body is the majority of phosphorus stored?

    <p>Bone</p> Signup and view all the answers

    Vitamin D aids in the absorption of calcium and __________.

    <p>phosphorus</p> Signup and view all the answers

    Match the following forms of phosphorus with their characteristics:

    <p>Organic Phosphorus = Predominantly intracellular Inorganic Phosphorus = Predominantly extracellular Hypophosphatemia = Serum level 1-2.5 mg/dL Calcium Absorption = Requires Vitamin D and calbindin</p> Signup and view all the answers

    Which of the following is NOT a cause of hypomagnesemia?

    <p>Diabetes insipidus</p> Signup and view all the answers

    Torsades de pointes is associated with a decreased QT interval.

    <p>False</p> Signup and view all the answers

    What is the recommended daily allowance (RDA) for magnesium?

    <p>420 mg (8.5 meq)/day</p> Signup and view all the answers

    In cases of severe hypomagnesemia with arrhythmia, IV __________ is administered.

    <p>MgSO4</p> Signup and view all the answers

    Match the following conditions with their related side effects:

    <p>Hypomagnesemia = Seizures Hypocalcemia = Tachyarrhythmia Digitalis toxicity = Increased potassium Gitelman syndrome = Na+-Cl- transporter defect</p> Signup and view all the answers

    What is the primary site of gastrointestinal absorption for magnesium?

    <p>Ileum</p> Signup and view all the answers

    Thiazide drugs can lead to hypomagnesemia by affecting magnesium absorption in the kidneys.

    <p>True</p> Signup and view all the answers

    Which syndrome is inherited that affects magnesium absorption?

    <p>Gitelman's syndrome</p> Signup and view all the answers

    Magnesium absorption in the kidney occurs primarily through the _____ pathway.

    <p>paracellular</p> Signup and view all the answers

    Match the following components with their functions:

    <p>TRPM6 = Transcellular transport of magnesium EGFR = Regulates magnesium absorption in the kidneys Claudin 16/19 = Facilitates paracellular magnesium reabsorption CaSR = Activated by blood calcium to enhance magnesium reabsorption</p> Signup and view all the answers

    Which of the following drugs is known to impair gastrointestinal absorption of magnesium?

    <p>Proton pump inhibitors (PPIs)</p> Signup and view all the answers

    Hypomagnesemia causes an increase in the secretion of parathyroid hormone (PTH).

    <p>False</p> Signup and view all the answers

    What is one common cause of hypermagnesemia related to medication intake?

    <p>Laxatives</p> Signup and view all the answers

    Symptoms such as cardiac arrest occur when magnesium levels exceed ______ meq/L.

    <p>72</p> Signup and view all the answers

    Match the conditions with their causes of hypermagnesemia:

    <p>Renal failure = Decreased Mg2+ excretion Tumor lysis syndrome = Extracellular shift Familial hypocalciuric hypercalcemia = Loss of function of CaSR Pre-eclampsia therapy = Mg2+ given as Rx</p> Signup and view all the answers

    Which of the following drugs is known to cause tubular injury?

    <p>Cisplatin</p> Signup and view all the answers

    In hungry bone syndrome, serum calcium levels are decreased.

    <p>True</p> Signup and view all the answers

    What causes pseudohypoparathyroidism?

    <p>GNAS gene mutation</p> Signup and view all the answers

    The infusion of intravenous calcium levels recommended for treating hypocalcemia is __________ grams per day.

    <p>3-5</p> Signup and view all the answers

    Match each type of pseudohypoparathyroidism with its characteristic:

    <p>PHP Type I = Increased calcium and phosphate levels PHP Type II = Decreased calcium and phosphate levels Pseudo PHP = Normal calcium, phosphate, and PTH levels</p> Signup and view all the answers

    Which characteristic feature is associated with Albright's Hereditary Osteodystrophy (AHO)?

    <p>Short 4th metacarpal bone longer than the metatarsal</p> Signup and view all the answers

    Short stature and round facies are associated findings of Down's Syndrome.

    <p>False</p> Signup and view all the answers

    What is the characteristic feature of Turner's Syndrome?

    <p>Short 4th metacarpal bone</p> Signup and view all the answers

    In Pseudohypoparathyroidism type 1a, the characteristic features include short _____ and _____ metacarpal bones.

    <p>4th, 5th</p> Signup and view all the answers

    Match the following conditions with their characteristic features:

    <p>Albright's Hereditary Osteodystrophy = Short 4th metacarpal bone longer than the metatarsal Down's Syndrome = Short 3rd metacarpal Turner's Syndrome = Short 4th metacarpal bone Pseudohypoparathyroidism type 1a = Short 4th and 5th metacarpal bones</p> Signup and view all the answers

    Study Notes

    Hypophosphatemia

    • Serum phosphorus levels < 1 mg/dl
    • May cause growth retardation, RBC hemolysis, rhabdomyolysis, cardiomyopathy, insulin resistance, proximal myopathy
    • Low phosphorus is a risk factor for rhabdomyolysis, but in the case of rhabdomyolysis, high phosphorus is observed.
    • Only severe vitamin D deficiency, severe low calcium levels cause low phosphorus.

    Causes of Hypophosphatemia

    • Nutritional vitamin D dependent rickets
    • Redistribution of phosphorus from blood to cells
      • Insulin after DKA (diabetic ketoacidosis)
      • Refeeding syndrome (most common metabolic abnormality - low phosphorus)
      • Hungry bone syndrome
    • Sepsis: Decreased calcium levels → decreased phosphorus levels
    • Heat stroke
    • Hyperthermia

    Treatment

    • Dialysis (best method)
    • Treat associated hypocalcemia
    • Restrict phosphorus intake
    • Avoid foods rich in phosphorus such as dairy products, pickles, nuts, chocolate, and dates

    Renal Causes

    • Increased excretion
    • Type II RTA (renal tubular acidosis)
    • Hypophosphatemic rickets
      • X-linked
      • Autosomal recessive
      • Autosomal dominant

    Gene Mutation and Outcome

    PatternGene mutationOutcomex linkedPHEX gene mutation - most commonDecreased cleavage of FGF 23Autosomal recessiveDMP mutationDecreased FGF 23Autosomal dominantFGF 23 mutationIncreased FGF 23

    Autosomal Dominant Hypophosphatemic Rickets

    • Lower limb predominant
    • Low serum phosphorus (due to increased FGF 23)
    • Increased ALP (alkaline phosphatase)

    Tubular Injury

    • Tumor induced osteomalacia (TIO): mesenchymal tumors → Gain of function mutation of FGF 23

    Management

    • Daily phosphorus requirement: 2 grams
    • Mild hypophosphatemia: Oral Adphos tablets (250 mg)
    • Low-fat milk (phosphorus content of 0.9 mg/ml)
    • Severe hypophosphatemia: IV phosphorus (10 mg/kg over 12 hours)

    Hyperphosphatemia

    • Medial calcification in vessels
    • Similar symptoms to hypocalcemia

    Causes

    • Excess phosphorus intake
      • Phosphate-containing enema (most common)
    • Decreased phosphorus excretion: renal failure or CKD (most common)
    • Redistribution of phosphorus from cells to blood
      • Rhabdomyolysis
      • Hemolysis
      • Tumor lysis syndrome
      • Respiratory or metabolic acidosis
    • Conditions producing 1α-hydroxylase
      • Acromegaly
      • Tumors (e.g., lymphomas)
      • Sarcoid cells
      • Granulomas
    • Familial tumoral calcinosis:
      • Autosomal recessive inheritance
      • Missense mutation (loss of function) of FGF-23

    Mechanism (Diagram)

    • Stress → Cells → Phosphate
    • Phosphate traps calcium
    • Decreased serum calcium levels, Increased serum phosphorus levels

    Phosphorus Excretion Impaired

    • Increased phosphorus reabsorption
    • Phosphorus traps calcium

    Calcific masses (CaPO₄) features

    • Most common in knee joint
    • Presents like tumors
    • Slow-growing soft tissue masses
    • Calcification shows up on X-ray

    Management

    • Phosphate binders (increase calcium excretion)
      • Examples: Sevalamer, Ferric citrate, Sucroferric oxyhydroxide

    Phosphorus in Kidney Disease

    • 99% of phosphorus is reabsorbed in the proximal convoluted tubule (PCT)
    • Na⁺-P cotransporter (II A & II C - secondary active transport)

    Types of Dysfunction

    • Fanconi syndrome/Type II RTA/Proximal RTA:
      • Generalized dysfunction of the PCT
      • Severe phosphate depletion leads to bone mineral changes and severe rickets
    • Chronic Kidney Disease (CKD):
      • Can lead to increased phosphorus
      • Early stages:
        • FGF-23 → Na⁺-P cotransporter → Phosphaturia → Normal serum phosphorus
        • Decreased calcium absorption due to impaired 1-alpha hydroxylase
      • End stages (ESKD):
        • FGF23 is inactivated (due to Klotho resistance)
        • Increased Serum phosphorus
        • Endothelial cell damage
        • Osteoblast activation leads to medial calcification
        • This can lead to the patient becoming unfit for renal transplant

    Notes

    • Vessel intimal calcification: Seen in atherosclerosis
    • Parathyroid Hormone (PTH): Increased (PTH (+))
    • Vitamin D: Increased (Vit D (+))
    • FGF-23: Decreased (FGF-23 (-) in early stages, inactivated in end stages)
    • Net effect of PTH and Vitamin D: Increases calcium (↑Ca²⁺) and decreases phosphorus (↓P)
    • Osteoblasts: Secrete FGF-23 and sclerostin

    Physiological Basis

    Serum Phosphorus

    • Hypophosphatemia: - 1-2.5 mg/dL: Asymptomatic. No RX needed - < 2.5 mg/dL : Symptomatic - < 4.5 mg/dL: Severe
    • Forms
      • Organic (intracellular): More
      • Inorganic (HPO42-): Extracellular in blood. Predominantly used to measure serum phosphorus

    Stores and Absorption

    CalciumPhosphorusTotal body stores1200 g500-800 g% in:Bone99.3%85%Soft tissue0.6%14%Extracellular fluid0.1%1%% bound to albumin40%10%AbsorptionCa2+ + PO43-Vit D +calbindin (Vit D binding protein)Reabsorbed from jejunum 20% Net absorption% absorbed from GIT95% Active60% Net absorption 5% Passive 80% Active (with vit D) 20% Passive

    Causes of Hypophosphatemia

    • Intracellular redistribution
      • DKA
      • Hungry bone syndrome
      • Refeeding
    • Acute pancreatitis
      • Decrease in calcium levels
      • Decrease in magnesium levels
    • Drugs:
      • PPI
      • Cisplatin, AGS
      • Cetuximab
      • Thiazides
    • Inherited diseases:
      • Gitelman syndrome: Na+-Cl- transporter defect
      • Bartter syndrome: Na+-K+-2Cl- symport defect
      • Hypomagnesemia: Claudin 16/19 defect
      • Hypocalciuria, stones
      • Isolated hypomagnesemia: TRPM6 defect

    Symptoms

    • Neuromuscular
      • Increased glutamate mediated excitability → Seizures
      • Vertical nystagmus
    • CVS:
      • Tachyarrhythmia
      • ECG abnormalities
    • Increased QT interval
      • Polymorphic VT
      • Torsades de pointes

    Associated Conditions

    • CVS
      • MI (myocardial infarction)
      • HTN (Hypertension)
    • Electrolyte imbalance
      • Decreased potassium levels (ROMK)
      • Decreased calcium levels
    • Other:
      • Insulin resistance
      • Migraine
      • Colon cancer

    Musculoskeletal

    • Decrease in bone mass

    ECG changes in hypomagnesemia

    Treatment

    • RDA: 420 mg (8.5 meq)/day
    • Mild: 3 MgO tablets (140 mg each)
    • Severe/arrhythmia:
      • IV MgSO4
        • Continue even after levels return to normal
        • 1-2 mg rapidly over 2 minutes
        • 4 g over next 24 hours
      • Amiodaride/Triamterine maybe tried

    Magnesium Metabolism

    Effect of Drugs

    • Impaired GI absorption: Proton pump inhibitors (PPIs)
    • Tubular injury:
      • Cisplatin
      • Aminoglycosides
      • Calcineurin
    • Defective transport pumps:
      • Thiazide and loop diuretics

    Hypermagnesemia

    Causes

    • Increased magnesium intake: Laxatives, purgatives, rectal enemas
    • Renal failure: Decreased magnesium excretion
    • Extracellular shift: Tumor lysis syndrome (TLS), Rhabdomyolysis, Hemolysis
    • Acromegaly: Increased phosphate and calcium levels
    • Familial hypocalciuric hypercalcemia: Loss of function of CaSR
    • Addison's disease: Volume loss
    • Pre-eclampsia therapy: Magnesium given as Rx

    Symptoms

    Blood Level (meq/L)Symptoms>72Cardiac arrest>10Flaccid quadriplegia, respiratory failure, hypocalcemia d/t PTH resistance, hypotension, bradycardia, decreased DTR (deep tendon reflex), flushing, headache, sluggish DTR.Arrhythmias: vague, no characteristic findings.6-104-6

    Hypomagnesemia

    Effect of Hypomagnesemia

    • Decreased magnesium levels
      • Patulous ROMK channel of THAL
        • Potassium loss
        • Decreased calcium levels
      • Decreased PTH (parathyroid hormone)
        • End organ resistance
    • Always check serum magnesium levels in relation to potassium or calcium levels.

    Treatment

    • Dialysis: For Chronic Kidney Disease (CKD)
    • Solute Toxicity: Calcium gluconate

    Normal Levels

    • 1.5 - 2.0 meq/L = 2.4 mg/dL

    Gastrointestinal Absorption

    • Site: Ileum (Along with bile acids)
    • Transport
    • Paracellular: 80-90%
    • Transcellular: mediated by TRPM6, TRPM7

    Kidney Absorption

    SiteContributionPathwayTransportTHAL65%ParacellularPassivePCT25%ParacellularPassiveDCT10%TranscellularActive

    • Net: 30%
    • Inherited: Gitelman's syndrome
    • Drug: Thiazide

    ThAL (Thick Ascending Limb)

    • Apical: EGF regulates TRPM6 (epidermal growth factor)
    • Basolateral: Regulated by Na+, K+, 2Cl-

    DCT (Distal convoluted tubule)

    • Basolateral: Regulated by Na+, K+, 2Cl-

    ThAL (Thick Ascending Limb)

    • Apical surface:
      • Blood calcium levels activate CaSR
      • Na, K, 2Cl- pump opens
        • Paracellular proteins (Claudin 16/19) drive calcium and magnesium reabsorption
      • Calcium enters cells
    • Basolateral surface:
      • Disorders of Na, K, 2Cl- pump:
        • Bartter Type 1: Hypercalciuria + Hypomagnesuria (80% patients)

    Mg2+^2+2+ transport in TAL & DCT (diagram)

    • Visual representation of various channels and transporters involved in magnesium transport

    Regulation

    • Regulated by:
      • Na+, K+, 2Cl-
      • EGFR Pathway

    Clinical implications:

    • Decreased magnesium by: Cetuximab/Anticancer drugs --> Hypomagnesemia

    Drugs

    • Bisphosphonates
    • Calcitonin
    • Citrate
    • Drugs causing tubular injury

    Sequence of Ruling out Causes

    • Decrease in serum calcium levels, check for corrected calcium levels to rule out
    • Magnesium deficiency to rule out

    Hungry Bone Syndrome

    Ca2+Ca^{2+}Ca2+PO43−PO_4^{3-}PO43−​PTHALPHungry Bone Syndrome↓↓↑(D/t matrix synthesis)Post op↓↑↓NormalHypoparathyroid↓↑↓Normal

    Hypocalcemia

    • Aminoglycosides
    • Cisplatin
    • Amphotericin &
    • Hypoparathyroidism
    • Other causes:
      • Intravenous calcium (3-5 g/day) and magnesium (2-6 g/day) infusion with oral calcitriol (1-3 µg/day) supplementation

    Zoledronate, Elcatonin, Parathyroidectomy

    • Graph showing adjusted serum calcium and serum ALP levels over time after parathyroidectomy.

    Pseudohypoparathyroidism (PHP)

    Pathogenesis

    • GNAS gene mutation → GSa defect → Resistance to PTH receptors.

    Types

    PHP Type IPHP Type IIPHP (Pseudo PHP)Ca2+Ca^{2+}Ca2+, S.PO43−S.PO_4^{3-}S.PO43−​, S.PTHS.PTHS.PTH↑ ↑ ↑↓ ↓ ↓Normal.Resistance to PTH++-Response to PTH administration++-Resistance to others++-Albright's Hereditary Osteodystrophy (AHO)+-+GS α\alphaα receptors ↓in blood+ (maternal defect)-+ (paternal)CAMP levelsCompletePartialNormal

    Albright's Hereditary Osteodystrophy (AHO)

    • Characteristic feature: Short 4th metacarpal bone is longer than the metatarsal
    • Associated findings: Short stature, round facies, and mental retardation.

    Down's Syndrome

    • Characteristic feature: Short 3rd metacarpal
    • Associated findings: Knuckle Dimple Knuckle Knuckle sign.

    Turner's Syndrome

    • Characteristic feature: Short 4th metacarpal bone
    • Associated findings: Knuckle Knuckle Dimple Knuckle sign.

    Pseudohypoparathyroidism type 1a

    • Characteristic feature: Short 4th and 5th metacarpal bones
    • Associated findings: Knuckle Knuckle Dimple Dimple sign.

    Normal

    • Characteristic feature: Clenched fist has all knuckles.

    Treatment of Acute Hypocalcemia

    • IV Infusion: 10 mL (1 amp) 10% Calcium Gluconate over 2-3 minutes. Administer 5 g in 500 mL of 5% Dextrose at 1-3 mg elemental calcium /kg/hr over 5 hours

    • Oral Calcium: Oral calcium supplements up to a certain amount per day

    • Images of hands and x-rays are included illustrating the physical features of each condition.

    • The diagrams show the location of knuckles and dimples on the hand.

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    Description

    This quiz covers the essential aspects of hypophosphatemia, including its causes, symptoms, and treatment options. It offers insights into the impact of low phosphorus levels on the body and associated conditions such as rhabdomyolysis and insulin resistance. Test your understanding of this metabolic disorder.

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