Diabetes Mellitus: Complications | Harrison's Endocrinology, 4e | AccessBiomedical Science

INTRODUCTION

Diabetes-related complications affect many organ systems and are responsible for the majority of morbidity and mortality associated with the disease. Strikingly, in the United States, diabetes is the leading cause of new blindness in adults, renal failure, and nontraumatic lower extremity amputation. Diabetes-related complications usually do not appear until the second decade of hyperglycemia. Because type 2 diabetes mellitus (DM) often has a long asymptomatic period of hyperglycemia before diagnosis, many individuals with type 2 DM have complications at the time of diagnosis. Fortunately, many of the diabetes-related complications can be prevented or delayed with early detection, aggressive glycemic control, and efforts to minimize the risks of complications.

Diabetes-related complications can be divided into vascular and nonvascular complications and are similar for type 1 and type 2 DM (Table 25-1). The vascular complications of DM are further subdivided into microvascular (retinopathy, neuropathy, nephropathy) and macrovascular complications (coronary heart disease [CHD], peripheral arterial disease [PAD], cerebrovascular disease). Microvascular complications are diabetes-specific, whereas macrovascular complications are similar to those in nondiabetics but occur at greater frequency in individuals with diabetes. Nonvascular complications include gastroparesis, infections, skin changes, and hearing loss. Whether type 2 DM increases the risk of dementia or impaired cognitive function is not clear.

TABLE 25-1DIABETES-RELATED COMPLICATIONS

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TABLE 25-1 DIABETES-RELATED COMPLICATIONS

Microvascular

Eye disease

Retinopathy (nonproliferative/proliferative)

Macular edema

Neuropathy

Sensory and motor (mono- and polyneuropathy)

Autonomic

Nephropathy (albuminuria and declining renal function)

Macrovascular

Coronary heart disease

Peripheral arterial disease

Cerebrovascular disease

Other

Gastrointestinal (gastroparesis, diarrhea)

Genitourinary (uropathy/sexual dysfunction)

Dermatologic

Infectious

Cataracts

Glaucoma

Cheiroarthropathya

Periodontal disease

Hearing loss

Other comorbid conditions associated with diabetes (relationship to hyperglycemia is uncertain): depression, obstructive sleep apnea, fatty liver disease, hip fracture, osteoporosis (in type 1 diabetes), cognitive impairment or dementia, low testosterone in men

^aThickened skin and reduced joint mobility.

GLYCEMIC CONTROL AND COMPLICATIONS

The microvascular complications of both type 1 and type 2 DM result from chronic hyperglycemia (Fig. 25-1). Evidence implicating a causative role for chronic hyperglycemia in the development of macrovascular complications is less conclusive. CHD events and mortality rate are two to four times greater in patients with type 2 DM and correlate with fasting and postprandial plasma glucose levels as well the hemoglobin A_1c (HbA_1c). Other factors such as dyslipidemia and hypertension also play important roles in macrovascular complications.

FIGURE 25-1

Relationship of glycemic control and diabetes duration to diabetic retinopathy. The progression of retinopathy in individuals in the Diabetes Control and Complications Trial is graphed as a function of the length of follow-up with different curves for different hemoglobin A_1c (HbA_1c) values. (Adapted from The Diabetes Control and Complications Trial Research Group: Diabetes 44:968, 1995.)