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ditor’s note: This month’s column takes a look at cellulitis and herpes zoster, which are common infections in geriatric dermatology.

Cellulitis

       Cellulitis is defined as “diffuse, spreading, acute inflammation within solid tissues, characterized by hyperemia, [white blood cell] infiltration, and edema without cellular necrosis or suppuration.”¹ The most common cause of superficial cellulitis is Streptococcus pyogenes. Staphylococcus aureus causes an infection that is less extensive than that of the streptococcal origin; it can produce a superficial cellulitis that usually occurs in association with an existing open wound or cutaneous abscess.
       Infection is most common in the lower extremities. Skin abnormalities, such as trauma, ulceration, tinea pedis (ie, athlete’s foot), or dermatitis, often precede the infection. Areas of lymphedema or other edema are also susceptible. While cellulitis is most commonly seen in the lower extremities, it can occur anywhere on the body. Because cellulitis is not a reportable disease, the exact incidence in long-term care is unknown. Following are suggestions for diagnosing and treating cellulitis.
       Diagnosis. Diagnosing cellulitis usually depends on the clinical findings. The major findings are local erythema and tenderness, frequently with inflammation of the lymphatic vessels and regional lymphadenopathy (abnormal enlargement of the lymph nodes). Large areas of ecchymosis are rare. The skin will be hot, red, and edematous, often with an infiltrated surface resembling the skin of an orange. The borders are usually indistinct, and petechiae are common. Blisters may develop and rupture, and necrosis of the involved skin can occur. Systemic manifestations, such as fever, chills, tachycardia, headache, hypotension, and delirium, may precede the cutaneous findings by several hours, but many patients do not appear ill.
       Treatment. Cellulitis can spread infection through the body quickly, resulting in bacteremia (presence of bacteria in the blood) or sepsis (infection in the blood). Other complications, such as thrombophlebitis or, rarely, gangrene, can develop, especially in older adults. Most patients who are appropriately treated recover completely. While rare, mortality can occur when highly virulent organisms cause cellulitis.
       Treatment for cellulitis consists of reducing edema and administering systemic antibiotics. For patients who do not have serious systemic illness, oral treatment is satisfactory. Do not be alarmed if the conditions of some patients worsen shortly after treatment. The killing of the causative organisms releases enzymes, such as streptokinase and hyaluronidase, leading to a higher fever, increased toxicity, and an increased white blood cell count.
       The treatment of tinea pedis in patients with leg cellulitis is also recommended to prevent further episodes; the fungal infections can allow bacteria to enter into the skin.

Herpes Zoster

       Herpes zoster is often referred to as “shingles” and occurs most often in the elderly. It is an infection that produces painful skin eruptions of fluid-filled blisters. Shingles is a condition caused by the same virus that causes chickenpox. It is believed that the varicella-zoster virus causes chickenpox in childhood, then lies dormant in nerve tissue for years or decades until it is reactivated to cause shingles.

Herpes zoster is caused by reactivation in adults of the varicella-zoster virus that causes chickenpox in children.

       While shingles can affect people at any age, it is more common and often more painful in older adults, with peak incidence between 50–70 years of age. Shingles usually affects otherwise healthy people, but immunosuppressed persons are at a higher risk. The higher incidence among elderly persons may be due to a decrease in cellular immunity. Other factors that predispose to a recurrence of the virus include the use of immunosuppressants or corticosteroids, malignancy, trauma, local irradiation, and surgery. Shingles recurs in about 6% of patients, usually at the same site as the initial episode. Once acquired, the virus cannot be eliminated.
       This acute disease occurs when the dormant virus becomes active. The active virus produces intense itching, pain, and grouped vesicles along a unilateral area of skin innervated by a certain nerve root, also known as a dermatome. It usually involves a single dermatome but can include other dermatomes.
       Shingles lesions are infectious until a dry crust appears. A person who has never had varicella may develop chickenpox after direct contact with the zoster lesions or with contaminated dressings. Usually, only young children are susceptible, although pregnant women and immunocompromised persons are also vulnerable. In long-term care facilities, direct contact precautions—not isolation—are recommended for susceptible persons until the lesions develop crusts. Suggestions for diagnosing and treating herpes zoster follow.
       Diagnosis. Before the lesions become visible, symptoms, such as chills, fever, malaise, gastrointestinal disturbance, and paresthesia or neuralgia, appear. Red and fluid-filled lesions resembling those of chickenpox usually appear along the affected area within 3 days. These eruptions develop rather rapidly into grouped vesicles that vary in size and may be hemorrhagic and very painful. As the condition progresses, new lesions continue to form and pain continues. If severe widespread distribution occurs, suspect an underlying lymphoma or other causes of immunodeficiency.
       The active phase may continue for a week or longer, but healing may require several weeks, especially in older adults. Normally, however, the vesicles begin to dry and crust after about 5 days.
       A dermatologist should be consulted immediately if shingles is suspected, as there are many complications that can arise from shingles. A blistery rash (known as disseminated zoster) may spread over a large portion of the body. If the shingles virus affects the nerves originating in the brain, serious complications involving the face, eyes, nose, and brain can develop. Areas of skin may have less sensitivity or a loss of feeling after shingles has healed. Particularly in the elderly, hyperpigmentation or scarring may result. Also, bacterial infection of the blisters may develop.
       The major difference between shingles in the elderly versus younger adults is the incidence of postherpetic neuralgia (persistent pain that lasts longer than 1 month after the rash has healed). The incidence of postherpetic neuralgia increases sharply with age, while its duration and severity increase even more markedly with age than does the incidence. This pain can be almost debilitating and, in some cases, has been known to persist for years.
       Rare complications of herpes zoster include encephalitis, corneal scarring, motor neuropathies, Guillain-Barré syndrome, and urinary retention (when sacral dermatomes are involved). Ophthalmic herpes zoster results from involvement of the ophthalmic division of the trigeminal nerve. Lesions on the tip of the nose indicate involvement of the ophthalmic and nasociliary nerves. Conjunctivitis, iridocyclitis, and keratitis may occur. In such cases, an ophthalmologic consultation should be sought. The risk of postherpetic neuralgia is greater with ophthalmic involvement than with involvement of other dermatomes. In some cases, if branches of the optical nerve are affected, vision may be impaired or even lost.
       The finding of multinucleate giant cells on a Tzanck smear or biopsy of a vesicle confirms a viral infection. Although not commonly needed, vesicle fluid culture or direct fluorescent antibody analysis can also identify the virus and distinguish it from herpes simplex.
       Treatment. Treatment for shingles includes a combination of antiviral drugs, steroids, antidepressants, anticonvulsants, and topical agents. Treatment with antiviral drugs is most effective in the early phase of shingles. Oral antivirals are appropriate if the elderly patient is seen within 3 days of the onset of the eruption. The severity and duration of an attack of shingles can be significantly reduced by immediate treatment with these drugs. These drugs may help reduce the risk of postherpetic neuralgia. If impetigo develops, the patient may need systemic antibiotics. Postherpetic neuralgia, once established, is difficult to treat. Analgesia of varying degrees is usually needed for the pain.