Late onset type 1 diabetes
BMJ 2012; 344 doi: https://doi.org/10.1136/bmj.e2827 (Published 30 April 2012) Cite this as: BMJ 2012;344:e2827
- Daniel Lasserson, senior clinical researcher1,
- Robin Fox, general practitioner2,
- Andrew Farmer, professor of general practice1
- 1University of Oxford, Department of Primary Care Health Sciences, Oxford OX1 2ET, UK
- 2The Health Centre, Bicester, UK
- Correspondence to: D Lasserson daniel.lasserson{at}phc.ox.ac.uk
A 41 year old man from an Indian family whose father had type 2 diabetes presented to his general practitioner with a four week history of increasing thirst and polyuria. He had not noticed any weight loss. Blood tests were arranged to confirm the diagnosis of diabetes. One week later, after having to push his car home, he began to feel exhausted and developed intermittent vomiting, which he attributed to exertion. Over the next two days he became more unwell, and the out of hours primary care service was contacted. He was reviewed urgently and admitted with diabetic ketoacidosis.
What is late onset type 1 diabetes?
A spectrum of autoimmune diabetes presents in adulthood, with type 1 diabetes characterised by the requirement of insulin at diagnosis to control glycaemia and prevent ketogenesis. Latent autoimmune diabetes of adulthood (LADA) also occurs but with much slower progression to requiring insulin after initial diagnosis.
Why is it missed?
Similar rates of ketoacidosis are seen in patients with type 1 diabetes at diagnosis in adulthood and childhood,3 and diagnostic delay is thought to account for many presentations with ketoacidosis in children.4 Although the classic symptoms produced by hyperglycaemia are unlikely to be missed, there may be a delay in accurately identifying patients requiring insulin at diagnosis if there is a clinical resemblance to type 2 diabetes at initial consultation. Family history is an important component of diagnostic reasoning in primary care, and, although type 2 diabetes has a strong familial link, the incidence of type 1 diabetes is also increased in relatives of patients with type 2 diabetes.5
Why does this matter?
Delay in diagnosis of type 1 diabetes can result in the development of ketoacidosis, requiring intensive management in secondary care. Patients may also be unnecessarily exposed to the risks from dehydration, acidosis, potassium shifts, and renal failure. Large cohort studies of patients with type 1 diabetes show that, although long term health has improved substantially for those with disease of childhood onset, this has not been the case for those with onset during adulthood,6 and mortality during the first two years after diagnosis is also higher in adult onset type 1 diabetes compared with childhood onset.7
How is type 1 diabetes diagnosed in adults?
Clinical features
A small cohort study reported that the classic symptoms of hyperglycaemia (thirst and polyuria) were observed at diagnosis of both adult and childhood onset type 1 diabetes, but the time course of symptoms was longer in adults (five weeks compared with two weeks) with less weight loss and few preceding superficial infections in the prodromal stage.3 In type 2 diabetes the prodrome of symptoms of hyperglycaemia can be longer, with 20% of patients symptomatic for up to six months before diagnosis.8 The symptoms and time course of type 1 diabetes can therefore overlap with those of type 2 diabetes, and there are no reliable clinical predictors from history and physical examination that will distinguish type 1 from type 2 diabetes in young adults. However, the National Institute for Health and Clinical Excellence (NICE) recommends that type 1 diabetes should be suspected if there is weight loss or lack of features of the metabolic syndrome in someone with newly diagnosed diabetes.9
If diabetic ketoacidosis has developed, common features are lethargy and vomiting with an increased respiratory rate and tachycardia, and in severe presentations, reduced level of consciousness, deep sighing respiration, and collapse.
Investigations
With new onset diabetes in young adults, the traditional categories of type 1 (insulin requiring) and type 2 (insulin resistant), which are oversimplifications, are not easily discriminated at initial presentation.10 The diagnostic criteria for diabetes, irrespective of type, are more straightforward, with random plasma glucose concentration ≥11.1 mmol/L and fasting plasma glucose concentration ≥7.0 mmol/L (in the presence of symptoms only one of these criteria is required).9 Diagnosis by means of HbA1c is not recommended for type 1 diabetes.
Although a large prospective cohort study showed that type 1 and type 2 diabetes can be differentiated using laboratory markers for aetiology and level of insulin secretion (autoantibodies and C peptide levels),11 they are not yet recommended for routine use in supporting diagnosis.
NICE recommends initial assessment for ketonuria as a marker of the need for exogenous insulin9 as other routinely ordered tests are unlikely to alert the clinician to the possibility of type 1 diabetes. Cohort studies based in secondary care show that up to 20% of patients with adult onset type 1 diabetes do not have ketonuria at presentation.3 However, there are no community based studies of late onset type 1 diabetes, so the prevalence of ketonuria at initial presentation in primary care is not known. Nevertheless, continuing review and reassessment may be needed when the initial diagnosis is unclear, particularly if there is rapid clinical deterioration.10 Making all patients with newly diagnosed diabetes in primary care aware of the symptoms of progression to ketoacidosis may prompt earlier healthcare contact for the minority who have type 1 diabetes that is initially misclassified as type 2.
How is late onset type 1 diabetes managed?
Initiate insulin at diagnosis to control blood glucose levels and suppress ketogenesis. Most patients will require acute assessment in secondary care for renal function, acid-base balance, and ketone body levels, as these will guide the need for intravenous therapy with insulin, fluid, and electrolytes. Detect and manage any underlying precipitants such as infection.
After initial stabilisation, a number of different insulin regimens may be suitable depending on agreed goals of therapy, although optimal glucose control requires long acting insulin to suppress fasting glucose levels and short acting insulin to reduce postprandial levels. Offer structured education encompassing dietary and lifestyle advice, self monitoring of blood glucose with adjustment of insulin doses, insulin treatment during periods of illness, and complications of diabetes. Undertake vascular risk assessment to identify and control risk factors with additional treatment. Coordination between primary and secondary care is essential to provide effective long term support.
Key points
Delay in diagnosis of adult onset type 1 diabetes can result in progression to ketoacidosis
Some families have a mix of type 1 and type 2 diabetes in their pedigrees, so family history is an unreliable guide for classifying type of diabetes
Routinely test for ketonuria on suspicion of diabetes in adults even if there is convincing evidence for type 2 diabetes
When making a diagnosis of type 2 diabetes in a young adult in primary care, ensure that the patient is aware of the symptoms of progression to ketoacidosis to prompt early healthcare contact for reassessment
Notes
Cite this as: BMJ 2012;344:e2827
Footnotes
This is one of a series of occasional articles highlighting conditions that may be more common than many doctors realise or may be missed at first presentation. The series advisers are Anthony Harnden, university lecturer in general practice, Department of Primary Care Health Sciences, University of Oxford, and Richard Lehman, general practitioner, Banbury. To suggest a topic for this series, please email us at easilymissed@bmj.com.
All authors contributed to reviewing relevant evidence and writing the manuscript. DSL is guarantor.
All authors have completed the Unified Competing Interest form at www.icmje.org/coi_disclosure.pdf (available on request from the corresponding author) and declare: no support from any organisation for the submitted work; no financial relationships with any organisations that might have an interest in the submitted work in the previous three years , no other relationships or activities that could appear to have influenced the submitted work.
Provenance and peer review: Commissioned and externally peer reviewed.
Patient consent obtained.