Diabetes mellitus (DM) is a disease caused by deficiency or diminished effectiveness of endogenous insulin. It is characterised by hyperglycaemia, deranged metabolism and sequelae predominantly affecting the vasculature. The main types of diabetes mellitus are:
- Type 1 diabetes mellitus: results from the body's failure to produce sufficient insulin.
- Type 2 diabetes mellitus: results from resistance to the insulin, often initially with normal or increased levels of circulating insulin.
- Gestational diabetes: pregnant women who have never had diabetes before but who have high blood sugar (glucose) levels during pregnancy are said to have gestational diabetes. Gestational diabetes affects about 4% of all pregnant women. It may precede development of type 2 (or rarely type 1) diabetes.
- Maturity-onset diabetes of the young (MODY) includes several forms of diabetes with monogenetic defects of beta-cell function (impaired insulin secretion), usually manifesting as mild hyperglycaemia at a young age, and usually inherited in an autosomal-dominant manner.
- Secondary diabetes: accounts for only 1-2% of patients with diabetes mellitus. Causes include:
- Pancreatic disease: cystic fibrosis, chronic pancreatitis, pancreatectomy, carcinoma of the pancreas.
- Endocrine: Cushing's syndrome, acromegaly, thyrotoxicosis, phaeochromocytoma, glucagonoma.
- Drug-induced: thiazide diuretics, corticosteroids, atypical antipsychotics, antiretroviral protease inhibitors.
- Congenital lipodystrophy.
- Acanthosis nigricans.
- Genetic: Wolfram syndrome (which is also referred to as DIDMOAD: diabetes insipidus, diabetes mellitus, optic atrophy and deafness), Friedreich's ataxia, dystrophia myotonica, haemochromatosis, glycogen storage diseases.
Some patients with type 2 diabetes require insulin, so the old terms of insulin-dependent diabetes mellitus (IDDM) for type 1 diabetes and non-insulin-dependent diabetes mellitus (NIDDM) for type 2 diabetes are inappropriate. Type 2 diabetes is increasingly diagnosed in children and adolescents and so the old term maturity-onset diabetes for type 2 diabetes is also inappropriate.
Type 1 diabetes mellitus
- Approximately 15% of those with diabetes - usually juvenile-onset, but may occur at any age. It may be associated with other autoimmune diseases. It is characterised by insulin deficiency.
- Concordance is >30% in identical twins; four genes are thought to be important. One (6q) determines islet sensitivity to damage - eg, from viruses or cross-reactivity from cow's milk-induced antibodies.
- Associated with HLA DR3 and DR4 and islet cell antibodies around the time of diagnosis. Patients always need insulin treatment and are prone to ketoacidosis.
- Risks of developing type 1 diabetes are broadly similar in all ethnic groups; however, there is increasing evidence that certain infectious agents or certain components of diet in early childhood trigger the development of autoimmunity to the pancreatic beta cells in genetically susceptible individuals.
- The term 'type 1a diabetes' is applied to the development of type 1 diabetes resulting from an autoimmune T cell-mediated islet cell destruction.
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Type 2 diabetes mellitus
- Approximately 85% of those with diabetes; they are usually older at presentation (usually >30 years of age) but it is increasingly diagnosed in children and adolescents.
- Type 2 diabetes is associated with excess body weight and physical inactivity.
- All racial groups are affected but increased prevalence in people of South Asian, African, African-Caribbean, Polynesian, Middle-Eastern and American-Indian ancestry.
- Caused by impaired insulin secretion and insulin resistance and has a gradual onset.
- Type 2 diabetics may eventually need insulin treatment.
- In 2011 there were 2.9 million people with diabetes. It is estimated that five million people will have diabetes in the UK by 2025.
- It is estimated that there are around 850,000 people in the UK who have diabetes but have not been diagnosed.
- The UK average prevalence of diabetes in the UK is 4.45% but there are variations between countries and regions.
- The proportion of people with diabetes increases with age.
- However, the incidence of diabetes is increasing in all age groups. Type 1 diabetes is increasing in children (especially those aged <5 years), and type 2 diabetes is increasing, particularly in black and minority ethnic groups.
Risk factors for type 2 diabetes
- Obesity, especially central (truncal) obesity.
- Lack of physical activity.
- Ethnicity: people of South Asian, African, African-Caribbean, Polynesian, Middle-Eastern and American-Indian descent are at greater risk of type 2 diabetes, compared with the white population.
- History of gestational diabetes.
- Impaired glucose tolerance.
- Impaired fasting glucose.
- Drug therapy, eg combined use of a thiazide diuretic with a beta-blocker.
- Low-fibre, high-glycaemic index diet.
- Metabolic syndrome.
- Polycystic ovarian syndrome.
- Family history (2.4-fold increased risk for type 2 diabetes).
- Adults who had low birth weight for gestational age.
- Patients with all types of diabetes may present with polyuria, polydipsia, lethargy, boils, pruritus vulvae or with frequent, recurrent or prolonged infections.
- Patients with type 1 diabetes may also present with weight loss, dehydration, ketonuria and hyperventilation. Presentation of type 1 diabetes tends to be acute with a short duration of symptoms.
- Presentation in patients with type 2 diabetes tends to be subacute with a longer duration of symptoms.
- Patients with diabetes may present with acute or chronic complications, as outlined in the section 'Complications', below.
- Diabetes may be diagnosed on the basis of one abnormal plasma glucose (random ≥11.1 mmol/L or fasting ≥7 mmol/L) in the presence of diabetic symptoms such as: thirst, increased urination, recurrent infections, weight loss, drowsiness and coma.
- In asymptomatic people with an abnormal random plasma glucose, two fasting venous plasma glucose samples in the abnormal range (≥7 mmol/L) are recommended for diagnosis.
- Two-hour venous plasma glucose concentration ≥11.1 mmol/L two hours after 75 g anhydrous glucose in an oral glucose tolerance test (OGTT).
- The World Health Organization (WHO) now recommends that glycated haemoglobin (HbA1c) can be used as a diagnostic test for diabetes. An HbA1c of 48 mmol/mol (6.5%) is recommended as the cut-off point for diagnosing diabetes. A value less than 48 mmol/mol does not exclude diabetes diagnosed using glucose tests.
Assessment and monitoring
- Assessment: see separate article Assessment of the Established Diabetic.
- Monitoring: see separate articles Glycated Haemoglobin and Self-Monitoring in Diabetes Mellitus.
The management plan for a person with diabetes includes:
- Diabetes education: structured education and self-management (at diagnosis and regularly reviewed and reinforced) to promote awareness.
- Diet and lifestyle: healthy diet, weight loss if the person is overweight, smoking cessation, regular physical exercise.
- Maximising glucose control while minimising adverse effects of treatment, such as hypoglycaemia.
- Reduction of other risk factors for complications of diabetes, including the early detection and management of hypertension, drug treatment to modify lipid levels and consideration of antiplatelet therapy with aspirin.
- Monitoring and early intervention for complications of diabetes, including cardiovascular disease, feet problems, eye problems, kidney problems and neuropathy.
A global assessment of an individual's cardiovascular risk is essential.
See separate articles:
- Management of Type 1 Diabetes.
- Management of Type 2 Diabetes.
- The Newly Diagnosed Diabetic.
- Diabetes Diet and Exercise.
- Diabetes Education and Self-management Programmes.
- Antihyperglycaemic Agents used for Type 2 Diabetes.
- Insulin Regimens.
- Precautions with Diabetic Patients Undergoing Surgery.
- Diabetes and Intercurrent Illness.
- Diabetes in Pregnancy.
Refer to separate articles under 'Acute' and 'Chronic' headings in this section.
- See Diabetic Ketoacidosis and Hyperosmolar Hyperglycaemic State.
- See Emergency Management of Hypoglycaemia.
- Cardiovascular disease: see ischaemic heart disease (Stable Angina, Acute Coronary Syndrome), Cerebrovascular Events and Peripheral Arterial Disease.
- See Diabetic Nephropathy.
- See Diabetic Retinopathy and Diabetic Eye Problems.
- See Diabetic Neuropathy, Autonomic Neuropathy and Neuropathic Pain and its Management.
- See Diabetic Foot, Leg Ulcers and Painful Foot.
- Frequent, recurrent and persistent infections.
- Type 1 diabetes:
- Over 60% of patients with type 1 diabetes have reasonably good health but many of the remainder develop blindness, end-stage renal disease and, in some cases, early death.
- If a person with type 1 diabetes survives the period 10-20 years after onset of disease without ongoing complications, they have a good chance of reasonably good health.
- Controlling blood glucose, lipids, blood pressure and weight are important prognostic factors.
- Type 2 diabetes:
- 75% of people with type 2 diabetes will die of heart disease and 15% of stroke.
- The mortality rate from cardiovascular disease is up to five times higher in people with diabetes than in people without diabetes.
- For every 1% increase in HbA1c level, the risk of death from a diabetes-related cause increases by 21%.
Type 1: despite a great deal of ongoing research, there are currently no interventions before diagnosis that have shown any benefit.
Type 2: see separate article Prevention of Type 2 Diabetes.
Further reading & references
- Maturity-onset Diabetes of The Young, Online Mendelian Inheritance in Man (OMIM)
- Wolfram Syndrome 1, WFS1; Online Mendelian Inheritance in Man (OMIM)
- Zhang L, Gianani R, Nakayama M, et al; Type 1 diabetes: chronic progressive autoimmune disease. Novartis Found Symp. 2008;292:85-94; discussion 94-8, 122-9, 202-3.
- Khardori R; Type 2 Diabetes Mellitus, Medscape, Sept 2012
- Diabetes in the UK 2012; Key statistics on diabetes, April 2012.
- Diabetes - type 2, Prodigy (July 2010)
- Use of Glycated Haemoglobin (HbA1c) in the Diagnosis of Diabetes Mellitus, World Health Organization (2011)
- Khardori R; Type 1 Diabetes Mellitus, Medscape, Aug 2012
- Wherrett DK, Daneman D; Prevention of type 1 diabetes. Pediatr Clin North Am. 2011 Oct;58(5):1257-70, xi.
|Original Author: Dr Hayley Willacy||Current Version: Dr Colin Tidy||Peer Reviewer: Dr Adrian Bonsall|
|Last Checked: 11/10/2012||Document ID: 2048 Version: 29||© EMIS|
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