Chapter 12-1: Approach to the Patient with Diabetes - Case 1

CHIEF COMPLAINT

CONSTRUCTING A DIFFERENTIAL DIAGNOSIS

The differential diagnosis of diabetes mellitus (DM) is actually a classification of the different types of diabetes:

1. Type 1 DM

   1. Of the persons with DM in Canada, the United States, and Europe, 5–10% have type 1.

   2. Caused by cellular-mediated autoimmune destruction of the pancreatic beta cells in genetically susceptible individuals, triggered by an undefined environmental agent

      1. Some combination of antibodies against islet cells, insulin, glutamic acid decarboxylase (GAD₆₅), or tyrosine phosphatases IA-2 and IA-2beta are found in 85–90% of patients.

      2. Strong HLA association

      3. Risk is 0.4% in patients without family history, 5–6% in siblings and children, and 30% in monozygotic twins.

      4. Patients are also prone to autoimmune thyroid disease, Addison disease, vitiligo, celiac disease, autoimmune hepatitis, myasthenia gravis, and pernicious anemia.

   3. Insulin therapy is always necessary.

   4. Because of the complete lack of insulin production, patients are at high risk for diabetic ketoacidosis (DKA).

2. Type 2 DM

   1. Caused by a progressive loss of beta cell insulin secretion frequently with underlying insulin resistance

   2. A heterogeneous disorder related to inflammation, metabolic stress, and genetic factors

3. Other, less common causes of diabetes

   1. Monogenic diabetes syndromes

   2. Exocrine pancreatic diseases that lead to the destruction of beta cells (pancreatitis, trauma, cystic fibrosis, pancreatectomy, pancreatic carcinoma)

   3. Endocrinopathies (acromegaly, Cushing syndrome, glucagonoma, pheochromocytoma)

   4. Drug or chemical-induced (corticosteroids, HIV/AIDS medications, after organ transplantation)

4. Gestational diabetes

Type 1 DM generally occurs in children, although approximately 7.5–10% of adults assumed to have type 2 DM actually have type 1, as defined by the presence of circulating antibodies. Type 2 DM is becoming more prevalent in teenagers and young adults, presumably related to the increased prevalence of obesity.

In most patients, the distinction between type 1 and type 2 DM is clear. Thus, the primary tasks of the clinician are to determine who should be tested for diabetes, who has diabetes, which complications to monitor, and how to treat the patient.