Declining cardiovascular function, poor circulation, diabetes, obesity, cancer, immunodeficiency, renal disease, and thinned, xerotic skin provide the setting for a host of bacterial infections in elderly persons that can involve any level or structure of the skin.
Declining cardiovascular function, poor circulation, diabetes, obesity, cancer, immunodeficiency, renal disease, and thinned, xerotic skin provide the setting for a host of bacterial infections in elderly persons that can involve any level or structure of the skin. Most of these infections are caused by Staphylococcus aureus or group A b-hemolytic streptococci. Group G streptococci are a common culprit in patients older than 50 years.
Cellulitis (A) and erysipelas (B) affect all age groups but are more common in elderly persons. Typical features are erythema, pain, swelling, warmth, and at least a low-grade fever. Some patients have a history of skin injury from surgery, trauma, insect bites, or punctures; however, there is often no predisposing condition.
Erysipelas affects the dermis, most commonly on the legs, and tends to be sharply demarcated. Cellulitis, which typically affects the lower legs, involves the subcutaneous fat and is often less well demarcated. Both types of infection can affect other areas, including the face (C), usually unilaterally but sometimes bilaterally. Cutaneous signs of infection are orange-peel (peau d'orange) skin, vesicles, and bullae. Red streaks radiating from an infected area represent progression of the infection into the lymphatic system. Regional lymphadenopathy and lymphangitis are occasional findings. Crepitus, most often found with anaerobic organisms, suggests an infection that is difficult to treat and is associated with increased morbidity and mortality.
The diagnosis of cellulitis or erysipelas is usually clinical. Complete blood cell counts often show leukocytosis with more than 13,000 white blood cells/µL. However, some patients do not have a fever or leukocytosis. In elderly patients and in persons with diabetes, numeric parameters such as temperature or white blood cell count cannot dictate treatment, because they are sensitive rather than specific markers of infection. Blood cultures are not usually cost-effective or necessary and should be ordered only if the patient is admitted to the hospital or has significant systemic symptoms, or if there is concern about bacteremia. Rare complications of cellulitis and erysipelas include septicemia, thrombophlebitis, septic arthritis, osteomyelitis, and endocarditis.
For streptococcal cellulitis or erysipelas, treatment consists of a penicillin or cephalosporin. Some experts recommend cephalexin, 500 mg qid, for 10 to 14 days. Cefdinir, 300 mg bid, is another option. For patients who are allergic to penicillin, azithromycin (500 mg on day 1, followed by 250 mg for 4 more days) is an alternative. Quinolones are considered third-line treatment for simple skin infections because they quickly generate resistance.
A patient who is in fragile health or who has significant comorbidities is generally admitted to the hospital for intravenous antibiotic treatment. Cellulitis associated with leg ulcers or pressure sores (sometimes classified as complicated skin structure infections) requires up to 3 to 4 weeks of treatment with intravenous antibiotics.
The differential diagnosis of cellulitis of the legs includes allergic contact dermatitis, deep venous thrombosis, and stasis dermatitis (D). Allergic contact dermatitis and stasis dermatitis tend to be bilateral. A predisposing factor for stasis dermatitis is venous incompetency, which may be suggested by a lack of hair on the shins. Because of diminished blood flow and breakdown of skin integrity, stasis dermatitis may result in secondary infection, whether superficial (impetigo or impetiginization) or deeper (erysipelas or cellulitis) (E).
Severe pain is a worrisome sign in any patient thought to have a skin infection. Red and painful legs warrant exclusion of a clotting disorder. Doppler ultrasonography or another imaging test should be ordered if there is any doubt about the diagnosis. Pain that is disproportionate to the clinical appearance of an eruption suggests the possibility of necrotizing fasciitis.