Type 1 diabetes: An introduction

Type 1 diabetes only accounts for an estimated 10% of all cases of diabetes in the UK (Diabetes UK, 2009), but has serious short- and long-term implications and its incidence continues to increase worldwide. The condition has a strong genetic component, inherited mainly through the human leukocyte antigen (HLA) complex. The factors that trigger onset of clinical disease, however, remain unclear – although several theories exist (Menser et al, 1978; Rewers and Zimmet, 2004).

Management of type 1 diabetes is best undertaken in the context of a multidisciplinary healthcare team and requires continuing attention to aspects such as insulin administration, blood glucose monitoring, meal planning, as well as screening for associated conditions and diabetes-related complications – predominantly microvascular and macrovascular disease. Newer treatment approaches, such as the use of continuous subcutaneous infusion pumps, have facilitated improved outcomes both in terms of glycaemic control and reduced risk of developing complications. However, the proliferation of type 2 diabetes threatens to overwhelm healthcare services and to obscure the healthcare implications and challenges of type 1 diabetes (Stumvoll et al, 2005).

The autoimmune cause of type 1 diabetes
Type 1 diabetes is a condition in which pancreatic beta-cell destruction usually leads to absolute insulin deficiency. There are two forms: type 1A results from a cell-mediated autoimmune attack on beta-cells, whereas type 1B is far less frequent, has no known cause, and occurs mostly in individuals of Asian or African descent who have varying degrees of insulin deficiency between sporadic episodes of diabetic ketoacidosis (DKA) (Devendra et al, 2004). This article will use type 1 diabetes to refer to type 1A diabetes.

The theory is that everyone is born with a varying degree of susceptibility to develop type 1 diabetes, which is largely inherited, residing predominantly in the HLA genotypes DR and DQ. The next step requires exposure to one or more environmental triggers that alter immune function, thereby initiating beta-cell destruction; suspects include viruses such as enterovirus and congenital rubella (Menser et al, 1978), cereals and food toxins (Rewers and Zimmet, 2004). This leads to abnormal activation of the T-cell-mediated immune system in susceptible individuals, which in turn causes an inflammatory response within the islets (insulitis) and beta-cell destruction. 

Antibodies, such as those raised against islet-cells and glutamic acid decarboxylase, are easily detectable, not only in those with type 1 diabetes but in close relatives, and can precede the clinical onset of the condition by many years (Barker et al, 2004). Supportive evidence for the autoimmune pathogenesis of type 1 diabetes comes from the susceptibility of people with autoantibodies for diabetes to other autoimmune conditions, including Hashimoto’s thyroiditis, Graves’ disease, Addison’s disease, coeliac disease, myasthenia gravis and vitiligo (Barker et al, 2005).

Epidemiology and prognosis
Traditionally, type 1 diabetes was regarded as a condition of people under the age of 20 years, often presenting with DKA. Mølbak et al (1994), however, suggest that only 50–60% of those with type 1 diabetes are younger than 16–18 years at presentation, and that type 1 occurs at a low incidence level throughout adulthood. There is, however, a significant trend towards decreasing age at presentation, particularly in children younger than 5 years (Lévy-Marchal et al, 2001), and according to the Department of Health (2007), 10–14 years is the peak age for diagnosis.

The incidence of type 1 diabetes is increasing by between 2% and 5% a year, and even in countries with the highest rates, such as Finland, there has been no levelling off since statistics records began in the 1950s (Gale, 2002). There is also huge geographical variation. Incidence rates in China, for example, are among the lowest in the world, with UK rates roughly 30 times higher, and almost 100-fold higher in Finland and Sardinia (Devendra et al, 2004). Evidence suggests that migrating populations also take on the incidence rates of their new countries in a short time. For example, incidence rates for type 1 diabetes in children of South Asian descent in the UK are similar to those of white or other ethnic populations in the same area, which are different to the very low rates reported in Asia (Raymond et al, 2001). 

Aside from the risk of complications, life expectancy for children up to the age of 18 years diagnosed with type 1 diabetes is reduced by between 15–20 years compared with healthy individuals (Narayan et al, 2003).

Treatment and management
Treatment of the sustained hyperglycaemia in type 1 diabetes is always with insulin, and the importance of intensive glycaemic control has come predominantly from the Diabetes Control and Complications Trial (DCCT Research Group, 1993) and its follow-up study (Nathan et al, 2005). 

The DCCT provided evidence of a close association between the degree of sustained glycaemic control and the onset or progression of microvascular complications (retinopathy, nephropathy and neuropathy; DCCT Research Group, 1993), and also macrovascular complications (cardiovascular, cerebrovascular, and peripheral vascular disease; Nathan et al, 2005), with no threshold effect, i.e. any decrease in HbA_1c concentrations is associated with a similar decline in relative risk of complications. There was also no HbA_1c level below which complications are completely prevented. 

In addition the central role of smoking, obesity, hypertension and hyperlipidaemia was also uncovered, and the benefits continue to be seen years after the initial interventions have ceased (Mühlhauser et al, 1996). This legacy effect – whereby intensive control in the early years of type 1 diabetes results in significant long-term risk reductions in developing micro- and macrovascular complications – demands that intensive management be instituted as soon as diabetes is diagnosed. The downside of this is the increased risk of hypoglycaemia with increasingly tight glycaemic control. On occasions, a basal–bolus regimen is not possible, either because of patient choice, insulin administration issues or injection site problems, and less intensive regimens may have to be used, such as twice-daily premixed regimens.

Increasing numbers of adults and children, particularly those with recurrent hypoglycaemia or difficult-to-control diabetes, are being offered insulin pumps (continuous subcutaneous insulin infusion), and primary care teams need to know how to get advice on the practical issues that people on pumps encounter (NICE, 2008).

Complications of type 1 diabetes
Microvascular complications
Diabetic nephropathy is the most common cause of renal failure in the developed world (Finne et al, 2005). It is typically defined by macroalbuminuria, the presence of which has been shown to be highly predictive of progression to advanced stages of diabetic nephropathy (DCCT/EDIC Research Group, 2003). Annual screening of people with type 1 diabetes can help to reverse the progression to end-stage renal failure if treatment with angiotensin-converting enzyme (ACE) inhibitors and angiotensin receptor blockers (ARBs) is initiated early on in the disease pathway (Fioretto and Solini, 2005). NICE (2004) recommends that blood pressure should be “maintained below 130/80 mmHg by addition of other antihypertensive drugs if necessary”, although the current Quality and Outcomes Framework indicator is 140/85 mmHg (NHS Employers, 2009).

Diabetic retinopathy is the most common cause of acquired blindness in people of working age in the Western world, with a prevalence rate for proliferative retinopathy of about 20–25% in type 1 diabetes (Fong et al, 2004). It progresses through recognisable stages: from early non-proliferative changes – previously called background retinopathy (microaneurysms, exudates and haemorrhages), which appear in almost all individuals with type 1 diabetes of about 20 years’ duration – to proliferative retinopathy (with risk of retinal detachment and vitreous haemorrhage) and macular oedema (Fong et al, 2004). Unlike early retinopathy, the later stages can be sight-threatening. Indeed, older people with type 1 diabetes of more than 20 years’ duration have a 90% chance of having diabetic retinopathy and 20% of these will progress to sight-threatening disease. 

Diabetic neuropathy often begins with a loss of sensation in the extremities. Signs and symptoms of diabetic neuropathy are outlined in Box 1. Diabetic neuropathy may be localised, for example carpal tunnel syndrome or diabetic amyotrophy, or generalised, such as sensorimotor polyneuropathy, which often presents as a peripheral neuropathy alone, but may also affect the autonomic system (diabetic autonomic neuropathy [DAN]) with cardiac dysfunction, gastroparesis and erectile dysfunction. 

One type of DAN – cardiac autonomic neuropathy (CAN) – may, at its mildest, impair exercise tolerance by impeding the reflex tachycardia associated with exercise or may cause orthostatic hypotension resulting in dizziness on standing. This may be a significant factor in the increased risk of falls in older people with type 2 diabetes (Schwartz et al, 2008). More seriously, CAN is responsible for silent myocardial infarctions in people with diabetes because of cardiac denervation. This is a particular problem during exercise when DAN can also cause decreased sweating, leading to a dangerous rise in body temperature, as well as in older people whose cardiac symptoms may present in unusual ways (epigastric pain, back pain) .

DAN may be a significant contributory factor in hypoglycaemic unawareness (Vinik et al, 2003), because the normal counter-regulatory system in which glucagon and adrenaline are secreted in response to hypoglycaemia is significantly impaired. This makes driving potentially hazardous. In addition, those with DAN may also have a problem driving at night because of a reduced or absent papillary response to light, which can easily be tested for. 

Peripheral neuropathy in conjunction with peripheral vascular disease can lead to neuropathic ulceration of the lower limbs (the diabetic foot), poor healing and gangrene, and amputation (Perkins and Bril, 2002). If nerve damage is also a problem, then the person may not be aware of the tissue damage. This is a common problem related to individuals of increasing age, poor eyesight, and reduced awareness, particularly those in residential care. 

For older individuals and those in residential care it is essential that staff and carers are aware of the importance of good foot care, and that any concerns about foot care are directed to a podiatrist. Changes in skin temperature may indicate neuropathy or infection, and if associated with a fallen arch should trigger an urgent referral to the “foot at risk” clinic. 

Macrovascular complications
Cardiovascular disease (CVD) accounts for about 52% of all deaths in people with type 2 diabetes and approximately 44% of deaths in type 1 diabetes (Morrish et al, 2001). The relative risk of CVD in type 1 diabetes can be as much as 10-fold greater than that in healthy individuals, and risk factors include the presence of diabetic nephropathy, but also DAN, dyslipidaemia, hypertension, and perhaps also specific microvascular cardiac disease (Perkins and Bril, 2005). 

The role of glycaemic control in type 1 diabetes has not been easy to define. The original results from the DCCT (1993) signified the importance of tight glycaemic control in terms of reducing the incidence of microvascular complications, although benefits in terms of macrovascular outcomes did not reach statistical significance. Data from the follow-up EDIC study (Nathan et al, 2005), however, did reach significance, linking intensive glycaemic control with a long-term reduction in the incidence of macrovascular complications.

Diabetic ketoacidosis 
DKA is a potentially life-threatening complication of diabetes resulting from hyperglycaemia due to absolute insulin shortage, causing elevated ketone levels in the blood and inducing metabolic acidosis (Kitabchi et al, 2007). 

The condition is often associated with new onset of diabetes in individuals with elevated blood glucose levels of >12 mmol/L, ketonuria and arterial blood pH less <7.35 (Singh, 1997). DKA can also occur in people with known diabetes, often as a result of intercurrent illness or poor compliance with insulin therapy. Symptoms include thirst, dry mouth, polyuria, nausea/vomiting and acetones on the breath (Table 1).

DKA usually presents as an acute medical emergency requiring urgent hospital treatment by continuous insulin infusion (to treat the hyperglycaemia) and electrolyte replacement (to restore acid balance). Prompt intervention by ketone testing – usually by blood test – frequent monitoring of blood glucose levels, and the use of insulin therapy can help to prevent DKA. 

Comorbid conditions
Clinical autoimmune thyroid disease occurs in about 5% of people with type 1 diabetes, although antithyroid antibodies are found in a third of people newly diagnosed with the condition, often presenting as Hashimoto’s thyroiditis (Kordonouri et al, 2005). 

Coeliac disease occurs in 3–10% of children with type 1 diabetes within 5 years of diagnosis, although many people with autoantibody and biopsy-positive coeliac disease remain asymptomatic (Hanukoglu et al, 2003; Barker et al, 2005). All people newly diagnosed with type 1 diabetes should be tested for both. 

The most common associated autoimmune condition is probably vitiligo, although accurate data are lacking (Gould et al, 1985). Other autoimmune conditions such as Addison’s disease and pernicious anaemia occur with greater frequency in people with type 1 diabetes – and indeed their first degree relatives – than in healthy individuals (Hanukoglu et al, 2003).

Psychological and social factors
Children and young people
Children with type 1 diabetes from single parent families and low socioeconomic status are more likely to present with DKA at diabetes onset, have more episodes of DKA during the course of their diabetes, attend the clinic less frequently, and are less likely to maintain good glycaemic control than those from two-parent and more affluent families (Jacobson et al, 1997). 

In a study by Kovacs et al (1992), 40% of teenagers had a period of persistent non-adherance with major aspects of their diabetes routines, and these individuals were more likely to show serious psychopathology – most commonly depression – in early adulthood. Both depression and eating disorders are more common in adolescents with type 1 diabetes, often resulting in insulin omission to control body weight, resulting in poor glycaemic control and early onset of diabetes-related complications (Jones et al, 2000). In the UK, support and advocacy both for children and their carers is available through Diabetes UK (www.diabetes.org.uk), who run camps for children with type 1 diabetes, and the Insulin Dependent Diabetes Trust (www.iddtinternational.org).

Primary care teams often look after schools and young offenders institutions, and it is very important that all staff are given basic training on type 1 diabetes, in particular, how to recognise and treat hypoglycaemia and hyperglycaemia (Table 1), and when to get assistance. The Diabetes UK (2006) document Children with Diabetes at School gives advice regarding what staff need to know if there are children with diabetes in their school, including information on insulin, food and eating times, recognising and treating hyper- and hypoglycaemia, physical activity, sickness and blood glucose monitoring.

Some teenagers and adolescents will not engage with conventional diabetes services. Such individuals pose a particular challenge, and primary care teams should liaise with local paediatric services to optimise care in this often hard-to-engage-with group. Some diabetes teams have developed text-messaging-based support systems with groups of young people with type 1 diabetes as a means of improving self-care skills and confidence. One such system (Franklin et al, 2006) was associated with improved self-efficacy and treatment adherence.

Evidence suggests that there is a temptation for parents and carers of young people with type 1 diabetes to become overprotective, which can lead to depression in the person with diabetes (Wilson et al, 2009). This overprotection, often borne out of ignorance, is equally present among peers of young people with the condition (Lehmkuhl et al, 2009).

Pregnancy
Planned pregnancy and pre-conceptual care with good glycaemic control before pregnancy reduces the rate of congenital malformations and improves outcomes (Confidential Enquiry into Maternal and Child Health [CEMACH], 2007; Box 2). In primary care it is essential to ask women with type 1 diabetes about their intentions regarding pregnancy and to discuss and record contraception decisions. Primary care teams should highlight the risks of unplanned pregnancy both for the mother (worsening retinopathy and nephropathy, pre-eclampsia and polyhydramnios) and for the baby (malformation, growth retardation, macrosomia and death in utero) (National Collaborating Centre for Women’s and Children’s Health [NCCWCH], 2008).

The CEMACH (2007) report outlined a range of factors associated with poorer pregnancy outcomes, including unplanned pregnancy, no contraceptive use in the 12 months before pregnancy, no folic acid commenced prior to pregnancy, smoking, and suboptimal glycaemic control before and during pregnancy.

All women with diabetes contemplating pregnancy should be advised to take 5 mg folic acid per day, and should be advised about smoking, alcohol and weight, and referred promptly to a local pre-conceptual care clinic (NCCWCH, 2008). In addition, statins, ACE inhibitors and ARBs are potentially teratogenic and should be stopped. 

Older people and those in residential care
The early onset of type 1 diabetes combined with its long duration contributes to the increased probability of microvascular and macrovascular complications being present in older people, many of whom may be in residential care (Box 3). As a result, complications are often exacerbated in this population, particularly nephropathy, retinopathy, neuropathy, peripheral vascular disease and the diabetic foot.

For those with type 1 diabetes in residential care, a treatment plan that is tailored to the individual is essential, particularly where the staff may be unqualified carers with limited knowledge of diabetes. Administration of insulin injections may be delegated to unqualified staff (delegate) by the district nurse responsible for the person’s care, providing the delegate has undertaken appropriate training and supervised practice, and has successfully completed both the theory and practice summative assessments. Staff will need to know:

• When to give injections.
• Which insulin to use.
• Where to inject the insulin.
• How to store the insulin.

It is also important that staff are aware of the importance of good foot care in residents with type 1 diabetes, as well as the referral pathway to podiatry services.

Occupational aspects of diabetes
Diabetes is a designated disability under the Disability Discrimination Act (2005), and as such, people with diabetes may not be unfairly discriminated against either in employment or when applying for jobs, and employers are expected to make reasonable adjustments to allow people with diabetes to work effectively alongside healthy people. 

The armed forces are exempt from this legislation and people diagnosed with diabetes in the armed forces are usually medically retired. Other than the armed forces, it is now illegal to impose a blanket recruitment ban on people with diabetes. There are some occupations, however, that people with type 1 diabetes are legally barred from undertaking (Box 4). It is unusual for the fire service to accept people with diabetes, but the police are increasingly taking recruits with the condition. From a safety perspective, the overwhelming issue is hypoglycaemia impairing function at work. This can often be minimised by work colleagues being familiar with the signs and treatment of hypoglycaemia, and this is particularly important with shift workers whose meal patterns and injection schedules may vary from day to day.

People with diabetes treated with insulin are barred from driving heavy goods vehicles or passenger carrying vehicles (Box 4); however, changes to C1 regulations in 2001 mean that “exceptional drivers” may be allowed to drive small lorries up to 7.5 tons (see Table 2; Driver and Vehicle Licensing Agency [DVLA], 2009). Taxi drivers are licensed by local authorities, not the DVLA, and as such are subject to each authority’s individual assessments regarding driving and diabetes. 

It is anticipated, however, that impending changes following the European Commission Working Group report on diabetes in 2006 will overhaul much of this legislation.

Practical issues
Lipohypertrophy and injection sites
Lipohypertrophy is a common side-effect of subcutaneous insulin therapy, characterised by swelling of subcutaneous fat at injection sites. Causes of lipohypertrophy include repeated injections to same site and reusing needles.

Injecting into a site of lipohypertrophy, although painless, can lead to unpredictable absorption of insulin, with the potential for poor glycaemic control. People with diabetes or persons responsible for administering insulin therapy should be aware of the correct procedure for subcutaneous injecting and should use the correct needle size for the individual. 

Sick day rules
Illness often stimulates increased glucose secretion, increasing the amount of insulin, fluids and blood glucose testing required. There are a number of “rules”, as well as practical tips and advice, to help people with type 1 diabetes better manage their condition when ill – the “golden rule” being that they should never stop taking their insulin. A comprehensive set of rules have been developed by NHS Tayside and can be found at: http://tinyurl.com/pfbx5b. This patient information leaflet goes into depth on the areas of food and drink, blood glucose and ketone monitoring, and insulin management.

Boxes 5 and 6 provide two case studies that highlight some of the practical issues related to the management of people with type 1 diabetes.

Clinical guidance
For England and Wales, NICE (2004) produced a guideline for the diagnosis and management of type 1 diabetes for children, young people and adults. The document outlines the care that should be available to adults with the condition, including recommendations on diagnosis and the options that should be offered. Equivalent recommendations regarding the diagnosis of type 1 diabetes in children and young people and about the care that should be available for them is also outlined, as well as information on transition to adult care (NICE, 2004). 

For Scotland, the Scottish Intercollegiate Guidelines Network (SIGN) is currently updating its 2001 guidance. This document also explores evidence-based diabetes care in children, young people and adults, including recommendations on lifestyle management, microvascular and macrovascular complications. Both documents cover the diagnosis, care and support of people with type 1 diabetes (SIGN, 2001; NICE, 2004), and should be a benchmark for any healthcare service.

Conclusion
Type 1 diabetes is becoming increasingly common and all people with this condition will contact their primary care team at some point. Understanding the pathophysiology, related complications, social aspects and treatment regarding this long-term condition will ensure that people with type 1 diabetes get the help and support they need, and will assist in building communication between primary and secondary care.

To complete the CPD module, click here.