Type 1 Diabetes Mellitus

Question 1

What is the definition of type 1 diabetes mellitus (T1DM)? [2]

Answer 1

a class of diabetes mellitus due to insulin deficiency / caused by autoimmune destruction of insulin-secreting pancreatic beta cells

Question 2

What is the epidemiology of T1DM? [4]

Answer 2

1. typically manifests in childhood and has an adolescent onset
2. patient is usually lean
3. concordance is ~30% in identical twins, indicating environmental influence
4. Latent autoimmune diabetes in adults (LADA) - slower progression to insulin dependence in later life

Question 3

What is the aetiology of T1DM? [3]

Answer 3

1. autoimmune disease with autoantibodies forming against insulin and pancreatic islet beta cells
2. idiopathic
3. genetic susceptibility with HLA-DR3 +/- HLA-DR4

Question 4

What are the risk factors for T1DM? [3]

Answer 4

1. family history - HLA-DR3 or HLA-DR4 in >90%
2. associated with other autoimmune diseases - autoimmune thyroid, coeliac disease, Addison’s disease, pernicious anaemia
3. environmental factors - dietary constituents, enteroviruses, vitamin D deficiency

Question 5

What is the pathophysiology of T1DM? [4]

Answer 5

1. autoimmune destruction of the pancreatic insulin-secreting beta cells by autoantibodies
2. this causes insulin deficiency as there is insufficient insulin production
3. continued breakdown of liver glycogen leading to glycosuria and ketonuria
4. when blood glucose increases and reaches 10mmol/L, the body can no longer absorb glucose, so polydipsia and polyuria in an attempt to remove excess glucose

Question 6

What causes diabetic ketoacidosis? [4]

Answer 6

1. results from a reduced supply of glucose and an increase in fatty acid oxidation
2. increased production of acetyl-CoA leading to ketone body production
3. that exceeds the ability of peripheral tissue to oxidise them, and lowers the pH of blood
4. acidification of blood impairs the ability of haemoglobin to bind to oxygen

Question 7

What is the clinical presentation of T1DM? [5]

Answer 7

1. patients with T1DM tend to be leaner
2. polyuria and nocturia - no more glucose can be absorbed, so high levels of glucose excreted in urine, which draws in water too, so excess loss of water and glucose
3. polydipsia - thirst due to loss of fluids and electrolytes
4. weight loss - due to fluid depletion and accelerated breakdown of fat and muscle
5. ketonuria - excess breakdown of fat and muscle, may progress to ketoacidosis if not treated

Question 8

How is T1DM diagnosed? [7]

Answer 8

symptomatic - 1 abnormal value

1. symptoms of hyperglycaemia - polyuria, polydipsia, unexplained weight loss, visual blurring, lethargy
2. fasting plasma glucose >7mmol/L OR
3. random plasma glucose >11.1mmol/L

asymptomatic - 2 abnormal values

1. fasting plasma glucose >7mmol/L AND/OR
2. random plasma glucose >11.1mmol/L AND/OR
3. oral glucose tolerance test (OGTT) - 2hr value >11.1mmol/L

haemoglobin A1c (HbA1c)
1. HbA1c >48mmol/mol (6.5%)

Question 9

What can cause secondary diabetes? [6]

Answer 9

1. pancreatitis/pancreatectomy
2. acromegaly
3. Addison’s disease
4. neoplasia of pancreas
5. Cushing’s syndrome
6. drugs - thiazides, beta-blockers

Question 10

What is the treatment for T1DM? [4]

Answer 10

1. insulin is always indicated in T1DM
2. synthetic insulin administered via subcutaneous injection
3. vital to educate patients on how to self-adjust insulin doses
4. modify diet and avoid binge drinking

Question 11

What are the two types of insulin? [2]

Answer 11

1. short-acting insulin - given before meals and starts working within 30-60 mins
2. long-acting insulin - used at bedtime and is slowly released from the injection site

Question 12

What are the complications of insulin treatment? [4]

Answer 12

1. hypoglycaemia
2. lipohypertrophy - at injection site
3. insulin resistance
4. weight gain