NEPHROPATHY CAN PROGRESS RAPIDLY
Elderly patients with diabetes are especially at risk of developing nephropathy, which progresses from microalbuminuria to overt proteinuria to renal insufficiency and end-stage renal disease. Nephropathy may develop over a shorter time than the typical 10 to 20 years in younger patients. Independent risk factors for proteinuria and renal insufficiency include poor glycemic control over many years, hypertension, longer duration of diabetes, male sex, high serum total cholesterol levels, and smoking. Elderly patients are also at risk of renal insults such as receiving intravenous iodinated contrast agents in the course of radiologic procedures, nephrotoxic drugs, and comorbid illness such as congestive heart failure.
The diagnosis of diabetic nephropathy is usually made clinically and not by renal biopsy. Diabetic nephropathy can be diagnosed with almost 100% specificity in type 1 diabetes and more than 85% specificity in type 2 diabetes by a urinary albumin excretion of more than 300 mg per day and an appropriate time course in the absence of other obvious causes of renal disease. The urinary albumin-to-creatinine ratio can be used to screen for microalbuminuria (the precursor of frank proteinuria and renal insufficiency). A value of more than 30 mg of albumin per gram of creatinine suggests that albumin excretion exceeds 30 mg and that microalbuminuria is present.
Prevention is a cornerstone of management. Good glycemic control reduces the risk of microalbuminuria, the progression of albuminuria, and the development of renal insufficiency. Lowering blood pressure reduces the decline in glomerular filtration rate and albuminuria. Angiotensin-converting enzyme (ACE) inhibitors reduce the rate of progression of proteinuria and reduce the rate of end-stage renal disease, although the data are stronger in patients with type 1 diabetes.34 When side effects such as cough limit the use of ACE inhibitors, angiotensin receptor blockers can be used as an alternative. Blood pressure should be controlled to reduce stroke and cardiovascular complications, regardless of whether microalbuminuria is present.35
End-stage renal disease in elderly patients with diabetes is becoming increasingly frequent. Nephropathy in older patients is different from that in younger patients. In elderly patients, the pathologic findings may suggest ischemia and hypertension, and the classic Kimmelstiel-Wilson lesions may be absent. Patients may present with end-stage renal disease following an episode of acute renal failure that does not resolve, which may occur after a radiologic procedure involving an iodinated contrast agent.
NONKETOTIC HYPEROSMOLAR COMA
Nonketotic hyperosmolar coma occurs predominantly in elderly patients with type 2 diabetes. Predisposing factors include dementia, infection, stroke, and myocardial infarction. Coma results from osmotic diuresis due to hyperglycemia and consequent dehydration. A drop in the glomerular filtration rate promotes further hyperglycemia and dehydration in a vicious circle. Glucose levels commonly reach 600 mg/dL or more, and serum osmolality often exceeds 320 mOsm/L. A fluid deficit of 5 to 10 L is typical.
Fluid replacement is the mainstay of treatment. Because free water is typically lost in an osmotic diuresis, 0.9% (normal) saline is usually given if hemodynamic instability is present or 0.45% (half-normal) saline otherwise. Insulin is also required, as is specific treatment of the precipitating cause, eg, infection. Ketoacidosis may also occur in the elderly.
Recovery from coma or improvement in mental status may lag behind correction of the serum osmolality and may take several days. Mortality rates can be high: severe hyperosmolarity, advanced age, and nursing home residence are the major risk factors for death.
INFECTIONS: SEVERE AND UNUSUAL
Elderly patients with diabetes are at increased risk of developing severe and unusual infections, particularly malignant external otitis. Necrotizing Pseudomonas aeruginosa infection initially involves the external ear canal and progresses to the mastoid air cells, the skull base, or temporal bone. The clinical presentation consists of fever, otalgia, otorrhea, and less commonly, cranial nerve palsy. Treatment involves surgical debridement and antibiotics.
Other infections associated with diabetes include rhinocerebral mucormycosis, necrotizing fasciitis, emphysematous cholecystitis, and emphysematous pyelonephritis. An elderly patient with diabetes is also at increased risk of renal papillary necrosis, which presents as insidious renal failure.
COGNITIVE IMPAIRMENT
Elderly people with diabetes are at increased risk of cognitive impairment, which poses a barrier to taking medications appropriately and performing other tasks of self-management.
Because dementia may go undetected, particularly in the early stages, cognitive function should be assessed in elderly patients when they fail to take therapy correctly or have frequent episodes of hypoglycemia, or if glycemic control deteriorates without an obvious explanation. Caregivers play a critical role in detecting and reporting early cognitive impairment.
DEPRESSION IS OFTEN UNDETECTED
Elderly patients with diabetes have a higher rate of depression than do age-matched controls, but it is commonly underdetected and undertreated.5,36 Depression has been associated with poor glycemic control, and treatment of depression is associated with improved control. Routine screening for depression should be performed; a variety of diagnostic instruments are available. Particular attention should be given to medications that are associated with depression.