Understanding pancreatic diabetes mellitus

Diabetes secondary to pancreatic diseases occurs when a pancreatic condition destroys both exocrine function (production of digestive enzymes) and endocrine function (production of insulin, glucagon and other hormones) [1]. The main causes include chronic pancreatitis, severe acute pancreatitis, pancreatic cancer, cystic fibrosis, hemochromatosis and pancreatic surgery. Unlike type 1 diabetes (autoimmune) or type 2 (insulin resistance), the destruction of the endocrine cells (alpha, beta, etc.) results from the pathological process of that pancreatic disease.

This form of diabetes accounts for 5-10% of all diabetes cases, but it is frequently misdiagnosed as type 2 diabetes [1]. The simultaneous loss of glucagon secretion (from the alpha cells) makes blood glucose very unstable, with an increased risk of severe hypoglycemia [2]. In addition, the associated exocrine pancreatic insufficiency requires supplementation with digestive enzymes for proper nutrient absorption.

Chronic pancreatitis causes diabetes through the progressive replacement of normal pancreatic tissue with fibrous and scar tissue [3]. Persistent inflammation gradually destroys the islets of Langerhans, where the beta cells (which produce insulin) and the alpha cells (which produce glucagon) are located. The process is gradual, and diabetes usually appears after years of chronic pancreatitis, as the amount of functioning pancreatic tissue decreases significantly.

The frequency of diabetes in chronic pancreatitis is generally 30% of cases, rising in proportion to the duration and severity of the disease [4]. The cause of the pancreatitis influences the risk of diabetes. Hereditary and alcoholic forms have higher rates of progression to diabetes [5]. Pancreatic calcifications and surgery for complications accelerate the loss of endocrine function. Patients with chronic pancreatitis should be screened for diabetes every year.

Pancreatic cancer causes diabetes through two main mechanisms. The first is the physical destruction of the islets of Langerhans by the growing tumor mass and by the inflammatory process around the tumor [6]. The second mechanism, which is more important, involves substances produced by the tumor that interfere at a distance with insulin secretion and action. Studies show that changes in blood glucose and unexplained weight loss can precede the diagnosis of pancreatic cancer by 2-3 years [6].

New-onset diabetes in people over 50 years of age, without the classic risk factors for type 2 diabetes, should raise suspicion of pancreatic cancer [7]. Some people with newly diagnosed diabetes at this age have undiscovered pancreatic cancer. The combination of recent diabetes, weight loss and a low level of fecal elastase significantly increases the likelihood of an underlying cancer and calls for prompt imaging investigations.

Type 3c diabetes (or pancreatogenic diabetes) is the term used for diabetes caused by diseases of the exocrine pancreas [8]. The diagnostic criteria include the presence of a documented pancreatic disease (chronic pancreatitis, pancreatic resection, cancer, cystic fibrosis), the absence of type 1 diabetes-specific autoantibodies, and evidence of exocrine pancreatic insufficiency. A low level of fecal elastase confirms impairment of exocrine function [1].

Signs that suggest type 3c diabetes include a history of pancreatitis or pancreatic surgery, large glycemic variability with frequent episodes of hypoglycemia, a low C-peptide (indicating reduced insulin reserve), and digestive symptoms such as steatorrhea (loose, very fatty stools) or abdominal pain [9]. This diagnosis is important because the treatment of the diabetes differs from the classic approach. You frequently need insulin from the start, pancreatic enzymes, fat-soluble vitamins and closer monitoring for the risk of hypoglycemia [2].

Cystic fibrosis affects the pancreas from intrauterine life onward, by producing viscous secretions that block the pancreatic ducts [10]. This obstruction leads to the progressive destruction of the exocrine tissue (which produces the digestive enzymes) and, later, of the endocrine tissue (the islets of Langerhans). About 85% of people with cystic fibrosis have exocrine pancreatic insufficiency from birth or in the first years of life.

Cystic fibrosis-related diabetes (CFRD) occurs in 20% of adolescents and in 40-50% of adults with this disease [11]. In CFRD, an insulin secretion deficit predominates (similar to type 1), but a degree of insulin resistance may also exist during periods of infection or treatment with glucocorticoids [10]. Annual screening with an oral glucose tolerance test is recommended starting at the age of 10. Insulin is the treatment of choice.

The likelihood of developing diabetes after a pancreatectomy depends on the amount of pancreatic tissue removed [12]. A total pancreatectomy leads to diabetes in 100% of cases, because you completely remove the insulin-producing beta cells. A partial pancreatectomy leads to diabetes in 20-50% of cases, depending on the type and extent of the resection, the location and the condition of the remaining pancreas [13].

Resection of the tail of the pancreas affects the islets of Langerhans more, as they are more concentrated in this area, and carries a higher risk of diabetes [12]. A pancreas already affected by chronic pancreatitis or fibrosis more often develops diabetes after any surgical intervention [13]. Postoperative glycemic control can be difficult because of the simultaneous loss of glucagon secretion, which increases the risk of severe hypoglycemia.

Hemochromatosis causes excessive iron accumulation in various organs, including the pancreas, where iron is deposited preferentially in the beta cells [14]. The excess iron generates free radicals (which damage the cell), causing severe oxidative stress. This toxic process progressively destroys the insulin-producing cells and leads to irreversible pancreatic fibrosis.

Diabetes occurs in 20-50% of patients with untreated hemochromatosis, with the percentage being highest in those with severe liver damage (cirrhosis) [14]. It is traditionally called "bronze diabetes" because of the associated skin pigmentation. Iron deposition also affects hepatic sensitivity to insulin, adding a component of resistance to insulin action [15]. Early diagnosis and treatment of hemochromatosis can prevent or slow progression to diabetes, but pancreatic lesions that are already established are usually permanent.

Yes, acute pancreatitis can lead to permanent diabetes in approximately 20-40% of cases, depending on severity and the duration of follow-up, especially after severe, necrotizing episodes [16]. Extensive necrosis of pancreatic tissue irreversibly destroys the beta cells in the islets of Langerhans. The risk rises in proportion to the severity of the acute episode and to the need for surgery for debridement (local cleaning) [17].

Diabetes can appear immediately after the acute episode or it can develop over the months and years that follow, as fibrosis replaces the normal pancreatic tissue [16]. Patients who have repeated episodes of acute pancreatitis have a higher cumulative risk of diabetes. Blood glucose monitoring is recommended for at least five years after a severe episode of acute pancreatitis, in order to detect diabetes early.

Pancreatic diabetes (type 3c) has a distinct mechanism from types 1 and 2 [1]. In type 1, the destruction of the beta cells is autoimmune, while in type 2 insulin resistance predominates. In type 3c diabetes, the loss of beta cells is due to the underlying pancreatic disease, such as chronic pancreatitis, pancreatic cancer or cystic fibrosis.

An important feature of pancreatic diabetes is the simultaneous loss of glucagon, which leads to an increased risk of severe hypoglycemia and wide glycemic fluctuations [2]. Patients frequently also have exocrine pancreatic insufficiency with steatorrhea and malabsorption [8]. Type 1 diabetes-specific autoantibodies are absent, and the C-peptide is variable, depending on the remaining beta cell mass.

To confirm the pancreatic origin of the diabetes, the doctor will request several categories of investigations [3]. Abdominal imaging by CT or MRI can show pancreatic calcifications, atrophy, pseudocysts or ductal changes suggestive of chronic pancreatitis. Endoscopic ultrasound provides additional details about the pancreatic parenchyma and ducts.

Exocrine function tests such as fecal elastase confirm exocrine pancreatic insufficiency [1]. Low levels of fat-soluble vitamins (A, D, E, K) suggest malabsorption due to exocrine pancreatic insufficiency. Type 1 diabetes-specific autoantibodies are negative. The C-peptide may be low or normal, depending on the residual beta cell reserve [9].