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‘Type 3c diabetes’ may be more common than type 1

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September 7, 2017

A diagnosis of diabetes following pancreatic disease is often classified as type 2 diabetes but presents with worse glycemic control and a higher need for insulin, according to findings published in Diabetes Care.

Simon de Lusignan, MD, MBBS, MSc, of the department of clinical and experimental medicine, University of Surrey in Guildford, Surrey, United Kingdom, and colleagues evaluated data from primary care records in England on 2,360,631 adults to determine the incidence of diabetes after pancreatic disease, to explore how clinicians classify patients and to compare the clinical characteristics of type 1 and type 2 diabetes. Records were evaluated from Jan. 1, 2005, to March 21, 2016.

Overall, there were 31,789 new diabetes diagnoses with 559 diagnosed after pancreatic disease. Participants with diabetes following pancreatic disease were further divided into two groups: diabetes after acute pancreatitis (n = 361) and diabetes after chronic pancreatic disease (n = 198). Follow-up was a median of 4.5 years from the date of diabetes diagnosis.

Incidence of adult-onset diabetes after pancreatic disease was higher compared with incidence of adult-onset type 1 diabetes (2.59 per 1,000 person-years vs. 1.64 per 1,000 person-years; P < .001); however, the highest incidence was found for adult-onset type 2 diabetes (142.89 per 1,000 person-years).

Diabetes of the exocrine pancreas was rarely used to classify diabetes after pancreatic disease (2.7%), which was most commonly classified as type 2 diabetes (87.8%).

At 1 year following diagnosis, poor glycemic control was more common in participants with diabetes after pancreatic disease compared with those with type 2 diabetes (40.3% vs. 32.5%; P < .001).

At 5 years, insulin use was most common in participants with diabetes after chronic pancreatic disease (45.8%), followed by diabetes after acute pancreatitis (20.9%) and type 2 diabetes (4.1%).

“Clinicians should elicit whether a patient has any history of pancreatic disease when they first present with diabetes and consider the diagnosis of diabetes of the exocrine pancreas,” the researchers wrote. “Diabetes of the exocrine pancreas must be appropriately recognized to tailor management, including choice of antihyperglycemic therapy and consideration of malabsorption requiring pancreatic enzyme and vitamin D prescription. Greater awareness of diabetes of the exocrine pancreas is required to appropriately manage this diabetes subgroup.” – by Amber Cox

Disclosures: de Lusignan reports he heads a diabetes Real World Evidence Centre funded by Eli Lilly and received a research grant from AstraZeneca. Please see the study for all other authors’ relevant financial disclosures.

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Andrew Stewart
Perspective

Diabetes most often results from one of two conditions. The most common is type 2 diabetes — formerly “adult onset” diabetes, due to a combination of insulin resistance and pancreatic beta cell failure. This accounts for some 26 million people in the United States. The second most common is type 1 diabetes, which accounts for some 2.5 million people in the United States. The older terms “juvenile” — previously used for type 1 diabetes — and “adult onset” — used for type 2 diabetes — have been abandoned because it is clear that adults may develop autoimmune (type 1) diabetes and children may develop insulin-resistant (type 2) diabetes.

The article makes many important points. First, it reminds patients and physicians that there are still other less common forms of diabetes, that despite their relative rarity, are still encountered because of the marked prevalence of all forms of diabetes, a prevalence that is increasing throughout the world. One example is maturity onset of diabetes in the young (MODY), a cluster of diabetes subtypes that share specific genetic defects that lead to inadequate beta cell mass and/or function. Another common example is glucocorticoid drug treatment (ie, prednisone, cortisone), which impairs both insulin action and beta cell survival or function. There are many other rare forms of diabetes. In this report, in an unselected series of 30,000 people recorded in an English public health system database during a 15-month period, the authors identified 559 people whose diabetes could be attributed to preceding pancreatitis or pancreatic surgery, conditions that are associated with beta cell loss and, therefore, inadequate insulin secretion.

One surprising note is that diabetes following pancreatic disease, called “type 3c diabetes” by some, usually went undiagnosed for years, because the onset was in adulthood and was simply assumed to be type 2 diabetes. Distinguishing between type 2 diabetes and pancreatic disease-associated diabetes makes a difference, because the former may be effectively treated with drugs other than insulin, whereas inadequate pancreatic insulin secretion must be managed by insulin treatment. Indeed, the patients with pancreatic diabetes in this series required insulin more often and were evidently undertreated because their HbA1c levels, a marker of good glucose control, were higher than the classical pattern in patients with type 2 diabetes.

Another surprise is that pancreatic disease-associated diabetes in this adult group (2.6 new cases per 100,000 person years) was actually more common than type 1 diabetes (1.6 new cases per 1000,000 person years). Most practicing physicians would probably not have guessed that this would be the case.

Another important parenthetic comment is that this study illustrates the power of single-provider health care systems that permit the rapid collecting of these types of population-based data. This is not currently possible in the United States, except in adults over 65 years covered by Medicare and except in veterans cared for by the VA Health System. These obviously miss a large part of the population.

Finally, readers may be interested to know that in large databases, such as the current report, or large health system databases, such as Medicare and the VA health system, it is not possible to define who precisely has type 1 diabetes and who has type 2 diabetes, because the tests required to define type 1 diabetes (ie, beta cell antibodies, C-peptide measurement and HLA genotypes) are not commonly performed, or may not be in the medical record. Thus, in most health systems as in this study, people are bundled into the type 2 diabetes rubric simply because they are adults, or perhaps adults with high BMI. Conversely, the type 1 diabetes label is attached if they have been assigned a diagnosis of type 1 diabetes as a billing code by a physician, but only a handful have actually been demonstrated by the strict criteria enumerated above to have type 1 diabetes. Thus, one final take-home message from the paper is that in addition to overlooking or mislabeling less common diabetes subtypes such as pancreatitis-related diabetes, the two common subtypes of diabetes are often confused as well. It is always interesting, and often helpful to the patient, to take a deeper diagnostic dive.

Andrew F. Stewart, MD

Director, Diabetes Obesity and Metabolism Institute
Irene and Dr. Arthur M. Fishberg Professor of Medicine
Icahn School of Medicine at Mount Sinai

Disclosure: Stewart reports no relevant financial disclosures.