Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

My MRCP > Metabolic Medicine > Flashcards

Metabolic Medicine Flashcards

1
Q

Vitamin D is relatively inactive. List the Vitamin D activation steps

A

Vitamin D is made in the skin following UV exposure to sunlight.
1,25(OH)2 vitamin D is made from vitamin D (D2 or D3 forms).
Both vitamin D2 and D3 undergo 25-hydroxylation in the liver and α-hydroxylation in the kidney to produce the activated form ,25(OH)2 vitamin D.
The rate-limiting step is the α-hydroxylation.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

Calcium - sites of reabsorption

A

Kidney - calcium is reabsorbed in the distal convoluting tubule
Gut - calcium is reabsorbed in duodenum and upper jejunum

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

Calcium, PTH, Vitamin D Axes - what happens if there is a drop in calcium serum level

A

Low blood Ca
Release of PTH by parathyroid gland
Increased vitamin D hydroxylation
Increased bone resorption
Increased Ca reabsorption in kidneys
Decrease in PO4 levels (increased excretion)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

Effects of PTH at high levels

A

High levels of PTH + poor control of serum phosphate and calcium-phosphate product in CKD causes increased cardiovascular disease risk and vascular calcification.
Calcific uraemic arteriolopathy (calciphylaxis), a painful ulcerating skin condition carrying a high mortality, is also a risk factor in patients with chronic kidney disease.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

Effects of Vitamin D

A
  • Gut: multiple actions on different proteins serve to increase absorption of calcium and phosphate.
  • Kidney: inhibits its own synthesis by reduced 1α-hydroxylase activity.
  • Parathyroid glands: inhibits PTH synthesis.
  • Bone: at high concentrations, activated vitamin D increases osteoclastic activity, promoting bone
    resorption.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

Hypercalcaemia - what are calcium levels adjusted and why are they necessary?

A

Calcium is protein-bound
Adjusted calcium concentration = Measured calcium + [(0.02 × (42-albumin level in g/L)].
A low adjusted calcium may be found in patients with severe hypoalbuminaemia, while true ionised calcium levels are normal.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

At what level will hypercalcemia be symptomatic? List the symptoms of hypercalcemia.

A
  • Adjusted calcium concentration >3.8 mmol/L carries risk of arrhythmias.
    Adjusted calcium concentration >3.0 mmol/L, usually causes symptoms.
    BONES
    STONES
    ABDOMINAL GROANS
    PSYCHIC MOANS
  • malaise, polyuria, polydipsia, nocturia, renal calculi, bone pain (due to osteitis fibrosa cystica), abdominal pain, nausea, constipation, dehydration, low mood and confusion.
  • Adjusted calcium concentration >3.8 mmol/L carries risk of arrhythmias.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

Causes of hypercalcemia [8]

A

Primary and tertiary hyperparathyroidism
Malignancy (cytokine release & production of PTH related peptide or calcitriol)
Thyrotoxicosis
Hypoadrenalism
Thiazide diuretics, excess Vit D, Milk-alkali syndrome
Immobility
Sarcoidosis
Familial hypocalciuric hypercalcemia

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

Primary, secondary & tertiary hyperparathyroidism
Why does secondary hyperPTH not cause hypercalcemia?

A
  • Primary hyperparathyroidism:
    ◆ Increased PTH due to parathyroid adenoma(s) or hyperplasia.
    ◆ 80% due to a benign solitary adenoma.
    ◆ MEN types 1 and 2A (2%)
    ◆ Characterised by high corrected serum and urine calcium, and low serum phosphate.
  • Tertiary hyperparathyroidism: autonomous secretion with high PTH despite hypercalcaemia.
    (Secondary hyperparathyroidism does not cause hypercalcaemia but is characterised by increased
    PTH in response to hypocalcaemia with low active vitamin D levels because of renal disease or dietary deficiency.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

Hypercalcemia Ix [10]

A
  • History: exclude iatrogenic causes and immobility; ask about symptoms of malignancy.
  • Examination: look for signs of malignancy and investigate as appropriate.
  • Blood tests for urea and electrolytes (to exclude renal impairment), calcium, PTH, vitamin D,
    phosphate and magnesium.
  • Urine test for calcium (ideally a 24-hour collection) and calcium:creatinine ratio to exclude familial
    hypocalciuric hypercalcaemia.
  • X-rays: look for characteristic sub-periosteal resorption of distal phalanges, tapering of distal
    clavicles, ‘salt and pepper pot’ skull lucencies and brown tumours of long bones.
  • If PTH levels are appropriately suppressed in the face of a normal PTH axis, check thyroid
    stimulating hormone (TSH), protein electrophoresis, urinary Bence–Jones protein and consider a Synacthen® (tetracosactide) test.
  • Parathyroid technetium (99mTc) sestamibi scan to identify parathyroid adenomas in primary
    hyperparathyroidism.
  • If all aforementioned tests are negative, investigate further for malignancy.
  • Dual energy X-ray absorptiometry (DEXA) scan for evidence of resulting osteoporosis.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

Hypercalcemia Treatment

A

Mild - monitor for renal stones
Moderate - fluid resuscitation, loop diuretic (furosemide)
Primary hyperparathyroidism - surgical resection
Cinacalcet
Glucocorticoids for cancer, sarcoidosis, vitamin D toxicity
Bisphosphonates

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

Calcinet for hypercalcemia

Mechanism of action? Indications?

A

Cinacalcet is a calcium sensing receptor agonist- acts on the parathyroid cells, mimics effect of hypercalcaemia, suppressing PTH synthesis and secretion.
Indications: tertiary hyperparathyroidism due to chronic kidney disease, primary hyperparathyroidism unsuitable for surgery and hypercalcaemia from malignancy not responding to treatment.
The combined use of vitamin D and calcimimetics has reduced the need for parathyroidectomy in the management of renal bone disease.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

Bisphosphonates for hypercalcemia

Mechanism of action? What is used in emergency? Chronic severe?

A
  • Bisphosphonates inhibit osteoclastic activity
  • prevent calcium release from bone.
  • Intravenous pamidronate - emergency situations.
  • Chronic severe hypercalcaemia may benefit from a bisphosphonate with a longer half-life (e.g. risedronate or zoledronic acid).
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

Hypocalaemia - severity classification into mild, moderate, severe

A
  • Adjusted calcium concentration 2.0–2.5 mmol/L is often asymptomatic.
  • Adjusted calcium concentration <2.0 mmol/L may cause symptoms
  • Adjusted calcium concentration <.8 mmol/L may result in arrhythmias or seizures, especially with a rapid fall in serum calcium.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

Symptoms of hypocalcemia

Give 3 points

A
  • Neuromuscular excitability, tetany and paraesthesiae of the extremities and perioral area, along with cramps and tetany.
  • Trousseau and Chvostek signs may be demonstrated
  • ECG may show a prolonged QTc interval.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

Causes of hypocalcemia Part 1

Causes of hypocalcaemia

Give 8 points

A
  • Lysis syndromes- rhabdomyolysis, tumour lysis syndrome, widespread release of phosphate from damaged cells binding to calcium, lowering serum levels.
  • Osteoblastic metastases with calcium uptake
  • Rx
  • DiGeorge syndrome (Ch22)
  • Acute pancreatitis (marker of severity)
  • Diet
  • CKD
  • Underactivity of PTH and vitamin D axes
  • Magnesium deficiency impairs PTH secretion and promotes resistance to the actions of PTH.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

Causes of hypocalcemia: Part 2

Which cancers are associated?
How does infusion of citrate blood products cause hypocalcaemia?
How does CKD cause hypocalcaemia?

A

Prostate, breast or bladder cancers cause osteoblastic mets with calcium uptake.
Infusion of citrate-containing blood products that can cause pronounced hypocalcaemia due
to citrate complexing with calcium.
CKD causes underactivity of axes:
Reduced hydroxylation of vit D > lack of active Vit D > unable to feedback to PTH to increase levels. Reduced phosphate excretion inhibits Vit D.

18
Q

What other causes can result in inactivity of PTH and vitamin D axes?

A
  • Hypoparathyroidism: associated with parathyroid damage, surgical removal (e.g. during
    thyroidectomy), autoimmune polyglandular endocrine syndromes and various mutations affect-
    ing the calcium sensing receptor.
  • Pseudohypoparathyroidism (Albright’s hereditary osteodystrophy): hypocalcaemia with
    measureable PTH, caused by end-organ resistance to the effects of PTH due to mutations.
19
Q

Hypocalcaemia: Investigation

A

History: ?chronic kidney disease, longstanding hypertension, diabetes mellitus, malabsorption and family history. Review medication.

Examination: ?malignancy, features of
chronic kidney disease or Albright’s hereditary osteodystrophy

  • Blood tests: bone profile, Mg, vitamin D, urea & Cr, LFTs, CK.
  • Urinary calcium and PO4 excretion.
  • Imaging: growth plate abnormalities in children, pseudofractures (Looser’s zones), reduced bone mineral density (BMD) on DEXA.
20
Q

Management of hypocalcaemia

CKD? Hypophosphatemic rickets? Oncogenic osteomalacia

A
  • CKD - 1-alpha hydroxylated vitamin D and alfacalcidiol corrects hypocalcaemia and suppresses PTH synthesis & secrertion.
  • Oncogenic osteomalacia requires tumour resection.
21
Q

Osteomalacia - bone profile?

A

low vitamin D levels
low calcium, phosphate (in around 30%)
raised alkaline phosphatase (in 95-100% of patients)

22
Q

Osteomalacia

Definition
Cause
Features

A

Osteomalacia
* Osteomalacia describes softening of the bones because of low vitamin D levels
* If this occurs in growing children it is referred to as rickets, with the term osteomalacia preferred for adults.
* vitamin D deficiency
* Features: bone pain, bone muscle tenderness, femoral neck fracture, proximal myopathy > waddling gait

23
Q

Osteomalacia

Radiological signs

A

translucent bands (Looser’s zones or pseudofractures)

Treatment includes loading dose vit D with ca supplementation

24
Q

Inherited metabolic disorders

Phenylketonuria

A

an inability to convert phenylalanine into tyrosine due to lack of phenylalanine hydroxylase. This results in hyperphenylalaninaemia and increased excretion of its metabolite, phenylpyruvic acid (‘phenylketone’) in the urine.

25
Q

Causes of hypoglycaemia

A
  • Most common: drug treated DM by sulfonylureas, insulin.
  • Rx: quinine, indoetacin
  • Alcohol inhibits gluconeogenesis
  • Hepatic failure impairs gluconeogenesis & glycogen storage
  • Hormonal deficiencies e.g., hypoadrenalism, GH, glucagon, thyroid deficiency
  • Insulinoma
  • Malignancies that consume glucose
  • NIPHS
  • Bariatric surgery
  • Neonatal
  • Genetic
26
Q

Hypoglycaemia

What is NIPHS?

A

Non insuloma pancreatogenous hypohlycaemia syndrome
- Hypertrophy and new formation of pancreatic islets cause increased insulin production & typically post-prandial hypoglycaemia.

27
Q

Hypoglycaemia: investigation in a non-diabetic adult

A

Non diabetic adult with glc <4mmol/L
* Insulin, c-peptide, anti-insulin antibodies
* Determine if there is endogenous hyperinsulinism - insulinoma
* If not, exogenous causes (rx), sepsis, malnutrition, end organ failure, hormone deficiency

28
Q

High density lipoprotein (HDL) vs LDL

A

HDL - transports cholesterol to liver
* Ways to increase HDL - reduce weight, increase exercise, alcohol in moderation, smoking cessation.
LDL - increased risk of atherosclerosis by entering vascular wall, being oxidised and promoting entry and activation of macrophages
* Way to decrease LDL & TC - reduce dietary fat & cholesterol, increase fibre

29
Q

Familial Hypercholesterolemia

A
  • AD inheritance
  • Xanthomata in tendon, iris
  • Associations: early onset CVD
  • Diagnosis confimed by genetic analysis
  • Mx: statins
30
Q

Drugs used in hyperlipidemia

  • 3-HMG COA reductase inhibitors
  • Fibrates

Mechanism of action, side effects, interactions

A
  • Competitive inhibition of enzyme involved in production of cholesterol from LDL. Statins may cause myositis, potentiates warfarin
  • Works on PPAR in liver increasing enzymes that clear triglyceride rich proteins from the blood, potentiates warfarin
31
Q

Ezetimibe

A

MOA: inhibits gut cholesterol absorption

32
Q

Inherited metabolic disorders

Phenylketonuria

A
  • usually presents by 6 months e.g. with developmental delay
  • child classically has fair hair and blue eyes
  • learning difficulties
  • seizures, typically infantile spasms
  • eczema
  • ‘musty’ odour to urine and sweat*
33
Q

Inherited metabolic disorders

Phenylketonuria
Diagnosis [3]
Management [3]

A

Diagnosis
* Guthrie test: the ‘heel-prick’ test done at 5-9 days of life - also looks for other biochemical disorders such as hypothyroidism
* hyperphenylalaninaemia
* phenylpyruvic acid in urine

Management
* poor evidence base to suggest strict diet prevents learning disabilities
* dietary restrictions are however important during pregnancy as genetically normal fetuses may be affected by high maternal phenylalanine levels
* Sapropterin is a new drug that activates residual phenylalanine hydroxylase, leading to improvement
of phenylalanine metabolism and decreasing phenylalanine concentrations

34
Q

Inherited Metabolic Disorders

Alkaptonuria

Pathophysiology, Presentation

A
  • Due to a deficiency of homogentisate dioxygenase (which is also part of the phenylalanine/tyrosine breakdown pathway).
  • Results in accumulation of homogentisic acid in cartilage and other tissues (ochronosis):
    ◆ blue/black discolouration of ear cartilage and sclera;
    ◆ spine and large joint arthritis;
    ◆ cardiac valve disease;
    ◆ renal calculi.
35
Q

Inherited Metabolic Disorders

Alkaptonuria

Diagnosis, Treatment [3]

A
  • Diagnosed by elevated homogentisic acid in urine; homogentisic acid also causes urine to turn red/
    black on standing.
  • Treatment is with a low phenylalanine and tyrosine diet. Vitamin C is a mild antioxidant.
  • Nitisinone, which blocks an upstream pathway in phenylalanine/tyrosine breakdown, is currently
    being evaluated for treatment.
36
Q

Inherited Metabolic Disorders

Homocystinuria

Presentation [5]

A
  • Due to a deficiency of cystathionine beta-synthase, a vitamin B6-dependent enzyme, involved in the breakdown of homocysteine to cysteine.
    Presentation:
  • often patients have fine, fair hair
  • Marfanoid body habitus: arachnodactyly etc osteoporosis, kyphosis
  • neurological: may have learning difficulties, seizures, ocular downwards (inferonasal) dislocation of lens, severe myopia
  • increased risk of arterial and venous thromboembolism
  • also malar flush, livedo reticularis
37
Q

Inherited Metabolic disorders

Homocystinuria

Investigations, Management

A
  • Diagnosis: elevated methionine and homocysteine (reduced sulphydryl monomer form) concentrations in plasma and increased homocystine (oxidised disulphide) concentration in urine.
  • cyanide-nitroprusside test: also positive in cystinuria
  • Depending on the exact genetic mutation, patients may respond to high dose vitamin B6, vitamin B12, folic acid, betaine or a methionine-restricted diet.
38
Q

Urea Cycle Disorders

Causes of hyperuricemia

3 mechanisms

A
  1. Underexcretion - most common
    * Decreased glomerular filtration (hypothyroidism, lead toxicity)
    * Decreased renal tubular secretion (DKA)
    * Increased renal tubular reabsorption (DI, anti-uricosuric drugs like diuretics)
  2. Overproduction
    * Exogenous from diet like offal, game.
    * Endogenous sources - HGPRT deficiency, Lesch-Nyhan syndrome.
  3. Combined mechanisms
39
Q

Inherited Metabolic Disorders: Urea cycle disorders

Causes of hyperuricema with combined mechanisms

combined mechanisms: Under-excretion and overproduction, 2 points

A

◆ Most commonly alcohol consumption that results in accelerated hepatic breakdown of ATP and the generation of organic acids that compete with urate for tubular secretion.
◆ Enzymatic defects such as glucose-6-phosphatase deficiency (Type I [von Gierke] GSD).

40
Q

Gout Management

Acute episodes, long term management

A
  • Treatment is with NSAIDs and colchicine for acute episodes.
  • NSAIDS or colchicine may be contraindicated or poorly tolerated by some groups patients (eg CKD)
  • Longer-term lowering of uric acid is achieved with allopurinol. Febuxostat (selective nonpurine xanthine oxidase inhibitor) has also been shown to effectively lower serum uric acid levels
  • Hyperuricaemia is associated with increased cardiovascular risk
41
Q

Gout management

What are alternatives if NSAIDs are not suitable for the patient?

A

short courses of oral steroids, or a long-acting intramuscular steroid injection, can be prescribed as an alternative.

42
Q

Osteoporosis vs Osteomalacia vs Pagets Disease on blood tests

PTH, Ca, PO4

A

Osteoporosis - doesnt affect blood tests
Osteomalacia -
* vitamin D low
* Low Ca
* Low phosphate
* Raised ALP

Pagets disease- ALP isolated rise

My MRCP (43 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions