Clinical Presentation of Type 2 Diabetes Mellitus

Clinical Presentation of Type 2 Diabetes Mellitus

Risk Factors

The risk factors for the development of both prediabetes and type 2 diabetes mellitus (T2DM) are as follows:1

  • Family history of diabetes mellitus
  • Cardiovascular disease
  • Being overweight or obese (BMI >25 kg/m2)
  • Sedentary lifestyle
  • Nonwhite ancestry
  • Previously identified impaired glucose tolerance, impaired fasting glucose, and/or metabolic syndrome
  • Hypertension
  • Increased levels of triglycerides, low concentrations of high-density lipoprotein cholesterol, or both
  • History of gestational diabetes mellitus
  • Delivery of a baby weighing more than 4 kg (9 lbs)
  • Polycystic ovary syndrome
  • Antipsychotic therapy for schizophrenia and/or severe bipolar disease

AACE recommends that all individuals aged ≥30 years who meet these criteria be screened.1 The American Diabetes Association (ADA) recommendations are similar: they suggest screening obese adults (aged ≥18 years) who have one or more diabetes risk factors, as well as screening everyone aged ≥45 years at least every 3 years. Negative screening tests should be repeated every 3 years, according to the ADA.2

Etiology

Type 2 diabetes is typically identified in persons older than 30 years who are overweight or obese and/or have a positive family history but do not have autoantibodies characteristic of type 1 diabetes mellitus (T1DM).  Most people with T2DM have evidence of insulin resistance (such as high triglycerides or low high-density lipoprotein cholesterol [HDL-C]).1

T2DM likely develops as a result of polygenic defects that predispose affected individuals to the disease. Environmental factors such as a sedentary lifestyle and a high-fat diet can exacerbate defects in both insulin secretion from pancreatic b-cells and insulin action in muscle and adipose tissues. The modest hyperglycemia characteristic of the prediabetic state (A1C 5.5% to 6.4%) results in glucotoxicity, while in overweight individuals (particularly those with central adiposity), elevated free fatty acid (FFA) levels lead to lipotoxicity. Both glucotoxicity and lipotoxicity worsen b-cell secretion, which in turn aggravates hyperglycemia. Once glucose levels rise above the diabetic threshold, T2DM ensues.3-6

Pathophysiology

Many organ systems are involved in the pathophysiology of T2DM, as follows:7

Organ System

Defect

Major Role

 

Pancreatic β-cells

Decreased insulin secretion

Muscle

Inefficient glucose uptake

Liver

Increased endogenous glucose secretion


Contributing Role

 

Adipose tissue

Increased FFA production

Digestive tract

Decreased incretin effect

Pancreatic α-cells

Increased glucagon secretion

Kidney

Increased glucose reabsorption

Nervous system

Neurotransmitter dysfunction

The complex interplay between these defects contributes to the ongoing progression of T2DM, although the disease itself results mainly from the first 3 defects: impaired insulin secretion from b-cells, impaired insulin action in muscle, and increased hepatic glucose production. Most patients will require a T2DM treatment approach that addresses more than 1 of these factors.

Natural History

T2DM develops and progressively worsens over time, as shown in this figure:

Initially, an increase in insulin resistance and impairments in b-cell function and the incretin effect interact, over time resulting in a relative insulin deficiency as well as excessive glucagon production (leading to overproduction of endogenous glucose in the liver). In response, first postprandial and then fasting blood glucose levels begin to rise.8-11

Hyperglycemia worsens all of the underlying pathophysiologic defects of T2DM.7 It is also an independent risk factor for macrovascular disease, the risks of which begin to increase during the prediabetic phase.12-14 Furthermore, hyperglycemia directly leads to the microvascular complications of diabetes.15-17

Because patients with early T2DM are often asymptomatic, the disease may not be diagnosed for many years after its onset.9,11 As a result, as many as 25% of patients have already developed 1 or more microvascular complications by the time of diagnosis.18

References

  1. Handelsman Y, Mechanick JI, Blonde L, et al. American Association of Clinical Endocrinologists Medical Guidelines for Clinical Practice for developing a diabetes mellitus comprehensive care plan. Endocr Pract. 2011;17(suppl 2):1-53.
  2. American Diabetes Association. Standards of medical care in diabetes—2013. Diabetes Care. 2013;36(suppl 1):S11-S66.
  3. Poitout V, Robertson RP. Glucolipotoxicity: fuel excess and beta-cell dysfunction. Endocr Rev. 2008;29:351-366.
  4. Kahn SE. The relative contributions of insulin resistance and beta-cell dysfunction to the pathophysiology of type 2 diabetes. Diabetologia. 2003;46:3-19.
  5. Gerich JE. Contributions of insulin-resistance and insulin-secretory defects to the pathogenesis of type 2 diabetes mellitus. Mayo Clin Proc. 2003;78:447-456.
  6. Kahn SE. Clinical review 135: The importance of beta-cell failure in the development and progression of type 2 diabetes. J Clin Endocrinol Metab. 2001;86:4047-4058.
  7. Defronzo RA. Banting Lecture. From the triumvirate to the ominous octet: a new paradigm for the treatment of type 2 diabetes mellitus. Diabetes. 2009;58:773-795.
  8. Holman RR. Assessing the potential for alpha-glucosidase inhibitors in prediabetic states. Diabetes Res Clin Pract. 1998;40(suppl):S21-S25.
  9. U.K. Prospective Diabetes Study Group. U.K. prospective diabetes study 16. Overview of 6 years' therapy of type II diabetes: a progressive disease. Diabetes. 1995;44:1249-1258.
  10. Ramlo-Halsted BA, Edelman SV. The natural history of type 2 diabetes. Implications for clinical practice. Prim Care. 1999;26:771-789.
  11. Nathan DM. Clinical practice. Initial management of glycemia in type 2 diabetes mellitus. N Engl J Med. 2002;347:1342-1349.
  12. Chiasson JL, Josse RG, Gomis R, Hanefeld M, Karasik A, Laakso M. Acarbose treatment and the risk of cardiovascular disease and hypertension in patients with impaired glucose tolerance: the STOP-NIDDM trial. JAMA. 2003;290:486-494.
  13. Malmberg K, Ryden L, Wedel H, et al. Intense metabolic control by means of insulin in patients with diabetes mellitus and acute myocardial infarction (DIGAMI 2): effects on mortality and morbidity. Eur Heart J. 2005;26:650-661.
  14. Selvin E, Marinopoulos S, Berkenblit G, et al. Meta-analysis: glycosylated hemoglobin and cardiovascular disease in diabetes mellitus. Ann Intern Med. 2004;141:421-431.
  15. UK Prospective Diabetes Study Group. Effect of intensive blood-glucose control with metformin on complications in overweight patients with type 2 diabetes (UKPDS 34). The Lancet. 1998;352:854-865.
  16. UK Prospective Diabetes Study Group. Intensive blood-glucose control with sulphonylureas or insulin compared with conventional treatment and risk of complications in patients with type 2 diabetes (UKPDS 33). Lancet. 1998;352:837-853.
  17. The Diabetes Control and Complications Trial Research Group. The effect of intensive treatment of diabetes on the development and progression of long-term complications in insulin-dependent diabetes mellitus. N Engl J Med. 1993;329:977-986.
  18. UK Prospective Diabetes Study (UKPDS). VIII. Study design, progress and performance. Diabetologia. 1991;34:877-890.