Theresa May became Prime Minister of the United Kingdom in July 2016; she is the first major world leader to have Type 1 diabetes. Ms. May was 56 years old in November 2012 when she was first diagnosed as having diabetes, but, as so many of us with adult-onset Type 1 diabetes have experienced, she was initially misdiagnosed as having Type 2 diabetes, an altogether different disease. Ms. May was correctly diagnosed as having Type 1 diabetes around May 2013, when the medication for Type 2 diabetes she was given did not work and she went for further tests that confirmed that she in fact had Type 1 diabetes. Thus, Ms. May spent about 6 months misdiagnosed and receiving incorrect treatment for the disease that she has. Ms. May said, “My very first reaction was that it’s impossible because at my age you don’t get it,” reflecting the misconception that only younger people get diagnosed with Type 1 diabetes.
A July 13, 2016 Medscape article on Theresa May “New UK Prime Minister Brings Spotlight to Type 1 Diabetes” sheds light on adult-onset Type 1 diabetes and the problem of misdiagnosis. Two endocrinologists who specialize in type 1 diabetes, Simon Heller, MD, professor of clinical diabetes at the University of Sheffield, United Kingdom, and Irl B. Hirsch, MD, professor of medicine at the University of Washington, Seattle (Dr. Hirsch has Type 1 diabetes), offered Medscape Medical News their thoughts on Ms. May's type 1 diabetes. Here are some nuggets from the Medscape article:
- Ms. May's story provides an important message to clinicians to consider the diagnosis of Type 1 autoimmune diabetes in adults whose clinical pictures do not fit those of classic type 2 diabetes.
- Ms. May was initially misdiagnosed with type 2 diabetes — a common occurrence in those who develop Type 1 autoimmune diabetes in adulthood.
- At the time Ms. May was diagnosed, much was said about how unusual her age was at diagnosis of type 1 diabetes. But actually, half of all people with autoimmune diabetes are diagnosed after age 18 years, and initial appearance in people in their 40s, 50s, and even older is not as rare as many medical textbooks claim. Dr. Hirsch says his oldest new-onset type 1 diabetes patient was 92, and Dr. Heller recently saw a new-onset type 1 diabetes patient in her late 50s with diabetic ketoacidosis (DKA).
- Unfortunately, like Ms. May, many adults with new-onset autoimmune diabetes are initially misdiagnosed with type 2 diabetes by primary-care clinicians, who simply write a metformin prescription when they see high blood sugar without appreciating other clues such as excessive weight loss without trying, extreme thirst, frequent urination, and a family history of not only type 1 diabetes but other autoimmune conditions including celiac and thyroid disease. For such patients — or those who aren't heavy to begin with, although obesity doesn't rule out type 1 diabetes — ordering an autoantibody panel [GAD, IA-2, IAA, and ZnT8] will help in making the correct diagnosis, both experts said.
- C-peptide levels are not a good indicator to distinguish between the diabetes types, Dr. Hirsch said, noting that data from his team suggest that people with older-onset type 1 diabetes may have more residual C-peptide function, which may confound their diagnosis but also make them less vulnerable to hypoglycemia. "When diagnosed with type 1 later in life, patients may continue to make a little endogenous insulin and that makes diabetes easier to control — they don't have giant swings or a big risk of low blood glucose levels."
And although many sources, such as this Medscape article, say that half of all cases of Type 1 diabetes are seen in adults, that statistic does not include the large number of people such as Ms. May who are misdiagnosed as having Type 2 diabetes. In many studies published since the first one in The Lancet in 1977, about 10% of people diagnosed with Type 2 diabetes have the autoantibody markers for Type 1 diabetes and have been misdiagnosed. In the United Kingdom Prospective Diabetes Study (UKPDS), about 10% of people diagnosed with “Type 2” diabetes were found to be autoantibody positive and had been misdiagnosed. Another credible source is “The Type 1 Diabetes Sourcebook” (ADA/JDRF 2013), in which Michael Haller MD states, "Adults with LADA [latent autoimmune diabetes in adults or slowly progressive Type 1 diabetes] may represent 10% of those adults incorrectly diagnosed with Type 2 diabetes. Clinicians treating adults must be aware of the need to screen for LADA, particularly in their patients with relatively low BMI."
I have hope that Ms. May’s initial misdiagnosis, and her age at diagnosis, will help to dispel myths about Type 1 diabetes and perhaps lead to more people with adult-onset Type 1 diabetes receiving the correct diagnosis and treatment.
 Sue Kirkman MD, professor of medicine at University of North Carolina and one of four authors of the American Diabetes Association position statement “Type 1 Diabetes Through the Life Span: A Position Statement of the American Diabetes Association” (Diabetes Care 2014; 37:2034–2054) says “Type 1 diabetes is a completely different disease than Type 2 and needs to be treated as such.”
 The Expert Committee on the Diagnosis and Classification of Diabetes Mellitus (ADA/WHO), as published in American Diabetes Association medical journals, says, "Although the specific etiologies of [Type 2] diabetes are not known, autoimmune destruction of beta-cells does not occur." The Expert Committee’s definition of Type 1 diabetes clearly encompasses all autoimmune diabetes, regardless of age (“Type 1 diabetes results from a cellular-mediated autoimmune destruction of the beta-cells of the pancreas. In Type 1 diabetes, the rate of beta-cell destruction is quite variable, being rapid in some individuals (mainly infants and children) and slow in others (mainly adults)).”
 Irvine WJ, McCallum CJ, Gray RS, Duncan LJP (1977) Clinical and pathogenic significance of pancreatic islet cell antibodies in diabetics treated with oral hypoglycaemic agents. Lancet 1: 1025–1027. In the Lancet study, 11% of study subjects were autoantibody positive. One conclusion of the study, “We believe that ICAb-positive diabetes controlled by oral hypoglycemic agents [O.H.A., medications for Type 2 diabetes] is an earlier stage in the same disease process (type 1 diabetes) that culminates in insulin-dependency.”
 Type 1 diabetes in adults can be acute-onset or slowly progressive. Slowly progressive Type 1 diabetes is sometimes called latent autoimmune diabetes in adults (LADA) or Type 1.5 diabetes. More recently, diabetes researchers have discouraged the use of the term latent autoimmune diabetes in adults, because LADA is not a latent disease. From The Type 1 Diabetes Sourcebook, “We consider all patients with evidence of autoimmunity to have Type 1 diabetes.”
 The Expert Committee on the Diagnosis and Classification of Diabetes Mellitus states, “