Diabetes mellitus

Imaad Razzaque, John E. Morley, Konrad C. Nau and Heather B. Congdon

CASE 1 Maria Sweetly (Part 1)

Maria Sweetly is a 72-year-old Hispanic woman who comes to your office for hypertension follow-up and remarks that for 2 months she has had bilateral burning and numbness of her feet and that she has fallen recently at home, without injury. Medications include hydrochlorothiazide 25 mg daily and metoprolol 50 mg twice a day. Her blood pressure is 160/88 mmHg, pulse 60 beats per minute, weight 173 lbs, and body mass index 30; monofilament and light touch sensation is diminished in a stocking distribution, Achilles reflexes are +1 dorsalis pedis pulses are +1 and the remainder of the examination is unremarkable. Fasting serum glucose is 130 mg/dL, blood urea nitrogen 19 mg/dL, and creatinine 1.2 mg/dL, and electrolytes are normal.

1. Can you name at least four of Mrs. Sweetly’s risk factors for diabetes?

2. Can you make the diagnosis of diabetes at this time?

3. What additional laboratory tests would you order?

Prevalence and impact

The prevalence of diabetes continues to increase steadily in the general population with a peak occurring between 60 to 74 years of age (Figure 41-1). Between 1995 and 2007 diabetes mellitus in the nursing home increased from 16.9% to 32.8% of residents.¹ Males tend to have a higher prevalence than females, and Hispanics and African Americans have a higher prevalence than whites.

Figure 41-1 Increasing prevalence of diabetes.

This increase in diabetes prevalence largely parallels the U.S. obesity epidemic.

Elderly persons diagnosed with diabetes have a similar spectrum of macrovascular and microvascular complications as is seen in their younger counterparts; however, the risk of cardiovascular disease is substantially higher. Older persons with diabetes are more likely to have an excess of functional disability, mobility impairment, depression, falls, incontinence, cognitive impairment, and cataracts.

More than half of direct medical expenditures on diabetes are for those persons over 65. One dollar in every $10 spent on health care in the United States in 2002 was for diabetes. Nineteen percent of personal health care expenditures in the United States are for diabetes mellitus (DM), although only 4.2% of the U.S. population is known to have diabetes. Adjusting for age, sex, and race/ethnicity, people with diabetes had medical expenditures 2.4 times higher than those without diabetes.²

The life expectancy at birth of people with diabetes was 64.7 and 70.7 years for men and women, respectively, compared with 77.5 and 81.4 years in those without diabetes in a 2004 Ontario study.² A British study of persons older than age 85 found that only 32% of the remaining life of persons with diabetes was active, whereas it was 42% for those without diabetes.³

Pathophysiology

There is a progressive continuum from the asymptomatic prediabetic state, with insulin resistance, through mild postprandial hyperglycemia and/or mild fasting hyperglycemia, to diagnosable type 2 diabetes.

Both an increased resistance to insulin-mediated glucose disposal and a decrease in non–insulin-mediated glucose uptake play a role in the development of diabetes mellitus in older persons.⁴^,⁵ Both aging and obesity play a role in producing these effects. The resistance to insulin-mediated glucose disposal is, in part, caused by triglyceride infiltration into muscle and mitochondrial defects in the muscle. However, older persons with diabetes mellitus are much less likely to be obese than middle-aged people with the disease. In older persons a reduction in glucose-induced insulin release from the pancreas is a larger component of the pathophysiology than is seen in middle-aged persons with type 2 diabetes mellitus. Older persons have fewer abnormalities in fasting hepatic glucose output compared to middle-aged persons. The differences in how diabetes mellitus manifests in older persons compared to how it appears in “classical” manifestations are highlighted in Table 41-1.

TABLE 41-1

Diabetes in Old Age Compared to “Classical” Types 1 and 2

Adiponectin, a hormone produced from adipocytes, reduces insulin resistance. Recently, fetuin-A (a hepatic alpha-fetoprotein) has been shown to produce insulin resistance, decrease adiponectin production, and increase inflammatory cytokine production from adipocytes. These findings suggest a number of factors are involved in the insulin resistance of aging.

Differential diagnosis and assessment

Presenting symptoms

Atypical or asymptomatic elders account for 30% of undiagnosed elders with diabetes. They do not have the “3 P’s” (polyphagia, polydipsia, polyuria).

The renal threshold for glucose increases with age because older persons often have a higher thirst threshold; thus glycosuria may not occur.⁵ Polydipsia can be absent; presentation in the elderly may be dehydration with altered thirst perception and delayed fluid supplementation. Polyuria can present as incontinence. More often, changes such as dry eyes, dry mouth, confusion, incontinence, or diabetic complications are the presenting symptoms.⁶

Elderly patients may occasionally have the presenting symptoms of weight loss or hyperosmolar nonketotic coma (HONKC). The common age-associated syndromes of persistent pain, urinary incontinence, cognitive impairment, depression, injurious falls, and polypharmacy are all increased in persons with diabetes; thus they are often the presenting problem.

Conversely, all elderly diabetics should be screened for these common syndromes within 3 to 6 months of diagnosis.⁷

Screening for and confirming the diagnosis

The laboratory diagnosis, similar to the pathophysiology, involves a continuum from prediabetes to the diabetic threshold (Boxes 41-1 and 41-2). The fasting blood glucose (FBS) of 126 mg/dL or greater is still the preferred test to screen for prediabetes and diabetes.⁸ It is easily available, and has a 95% confidence interval (±18%) when performed on fasting venous plasma glucose samples (FPG).⁹