Porth's Essentials of Pathophysiology, 4e

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Diabetes Mellitus and the Metabolic Syndrome

C h a p t e r 3 3

the abnormal focus of pressure is coupled with loss of sensation, a foot ulcer can occur. Common sites of trauma are the back of the heel, the plantar metatar- sal area, or the great toe, where weight is borne during walking (Fig. 33-12). All persons with diabetes should receive a full foot examination at least once a year. This examination should include assessment of protective sensation, foot structure and biomechanics, vascular status, and skin integrity. 3,61 Evaluation should include a somatosen- sory test using the Semmes-Weinstein monofilament, a simple, inexpensive device for testing loss of protec- tive sensation (Fig. 33-13). The monofilament is held in the hand or attached to a handle at one end. When the unattached or unsupported end of the monofilament is pressed against the skin until it buckles or bends slightly, it delivers 10 g of pressure at the point of contact. 61 The person tested reports when he or she is being touched by the monofilament. Usually four sites per foot are touched. An incorrect response at even one site indi- cates loss of protective sensation and increased risk of ulceration. Because of the constant risk of foot problems, it is important that people with diabetes wear shoes that have been fitted correctly and inspect their feet daily, looking for blisters, open sores, and fungal infection (e.g., ath- lete’s foot) between the toes. If their eyesight is poor, a family member should do this for them. In the event a lesion is detected, prompt medical attention is needed to prevent serious complications. Specially designed shoes have been demonstrated to be effective in preventing relapses in people with previous ulcerations. 61 Because cold produces vasoconstriction, appropriate foot cov- erings should be used to keep the feet warm and dry. Toenails should be cut straight across to prevent ingrown toenails. The toenails often are thickened and deformed, requiring the services of a podiatrist. Smoking should be

FIGURE 33-13. Use of a monofilament in testing for impaired sensation in the foot of a person with diabetes.

avoided because it causes vasoconstriction and contrib- utes to vascular disease. Cardiovascular risk factors should be addressed in patients with diabetic foot ulcers and peripheral arte- rial disease. Ulcers that are resistant to standard therapy may respond to application of growth factors. Growth factors provide a means by which cells communicate with each other and can have profound effects on cell proliferation, migration, and extracellular matrix syn- thesis. For example, becaplermin, a topical preparation of recombinant human platelet-derived growth factor, is used in the treatment of neuropathic lower extremity ulcers. Infections Although not specifically an acute or a chronic com- plication, infections are a common concern of people with diabetes. Certain types of infections occur with increased frequency in people with diabetes: soft tissue infections of the extremities, osteomyelitis, urinary tract infections and pyelonephritis, candidal infections of the skin and mucous surfaces, dental caries and periodontal disease, and tuberculosis. 62,63 Moreover, infections often are more serious in people with diabetes. Suboptimal response to infection in a person with diabetes is caused by the presence of chronic complica- tions, such as vascular disease and neuropathies, and by the presence of hyperglycemia and altered neutro- phil function. Sensory deficits may cause a person with diabetes to ignore minor trauma and infection, and vascular disease may impair circulation and delivery of blood cells and other substances needed to produce an adequate inflammatory response and effect healing. Pyelonephritis and urinary tract infections are rela- tively common in persons with diabetes, and it has been suggested that these infections may bear some relation to the presence of a neurogenic bladder or nephroscler- otic changes in the kidneys. Hyperglycemia and glycos- uria (including treatment with SGLT2 inhibitors) may influence the growth of microorganisms and increase the severity of the infection. Diabetes and elevated

FIGURE 33-12. Neuropathic ulcers occur on pressure points in areas with diminished sensation in diabetic polyneuropathy. Pain is absent (and therefore the ulcer may go unnoticed). (From Bates BB. A Guide to Physical Examination and History Taking. 6th ed. Philadelphia, PA: J.B. Lippincott; 1995.)