Departamento de Neuroimagen

Bacterial skin infections most commonly include cellulitis, impetigo, and folliculitis.

I. Cellulitis

A. Cellulitis is a painful, erythematous infection of the

dermis and subcutaneous tissues that is character- ized by warmth, edema, and advancing borders. Cellulitis commonly occurs near breaks in the skin, such as surgical wounds, trauma, tinea infections, or ulcerations. Patients may have a fever and an elevated white blood cell count. The most common sites of cellulitis are the legs and digits, followed by the face, feet, hands, torso, neck, and buttocks.

B. In otherwise healthy adults, isolation of an etiologic

agent is difficult and unrewarding. If the patient has diabetes, an immunocompromising disease, or persistent inflammation, blood cultures or aspira- tion of the area of maximal inflammation may be useful.

C. Empiric treatment of infection in patients with- out diabetes:

1. P e n i c i l l i n a s e - r e s i s t a n t p e n i c i l l i n : Dicloxacillin (Pathocil) 40 mg/kg/day in 4

divided doses for 7-12 days; adults: 500 mg qid or

2. First-generation cephalosporin: Cephalexin (Keflex) 50 mg/kg/day PO in 4 divided doses

for 7-10 days; adults: 500 mg PO qid or

3. Amoxicillin/clavulanate (Augmentin) 500 mg

tid or 875 mg bid for 7-10 days.

4. Azithromycin (Zithromax) 500 mg on day 1,

then 250 mg PO qd for 4 days.

5. Erythromycin ethylsuccinate 40 mg/kg/day in

3 divided doses for 7-10 days; adults: 250-500 mg qid.

6. Limited disease can be treated orally, but more

extensive disease requires parenteral therapy. Marking the margins of erythema with ink is helpful in following the progression or regression of cellulitis.

7. Outpatient therapy with injected ceftriaxone

(Rocephin) provides 24 hours of parenteral coverage and may be an option for some pa- tients.

Descriptions of Bacterial Skin Infections

Disease Description

Carbuncle A network of furuncles connected by sinus tracts

Cellulitis Painful, erythematous infection of deep skin with poorly demarcated borders Erysipelas Fiery red, painful infection of superficial

skin with sharply demarcated borders Folliculitis Papular or pustular inflammation of hair

follicles

Furuncle Painful, firm or fluctuant abscess originat- ing from a hair follicle

Impetigo Large vesicles and/or honey-crusted sores

D. Antibiotics should be maintained for at least three

days after the resolution of acute inflammation. Adjunctive therapy includes cool compresses; appropriate analgesics for pain; tetanus immuniza- tion; and immobilization and elevation of the affected extremity.

E. A parenteral second- or third-generation

cephalosporin (with or without an aminoglycoside) should be considered in patients who have diabe- tes, immunocompromised patients, those with unresponsive infections, or in young children. The patient may also require a plain radiograph of the area or surgical debridement to evaluate for gas gangrene, osteomyelitis, or necrotizing fasciitis.

F. Periorbital cellulitis is caused by the same organ-

isms that cause other forms of cellulitis and is treated with warm soaks, oral antibiotics, and close follow-up. Children with periorbital or orbital cellulitis often have underlying sinusitis. If the child is febrile and appears toxic, blood cultures should be performed and lumbar puncture considered.

G. Orbital cellulitis occurs when the infection passes

the orbital septum and is manifested by proptosis, orbital pain, restricted eye movement, visual disturbances, and concomitant sinusitis. This ocular emergency requires intravenous antibiotics, otorhinolaryngology, and ophthalmologic consulta- tion.

II. Erysipelas

A. Erysipelas usually presents as an intensely

erythematous infection with clearly demarcated raised margins and lymphatic streaking. Common sites are the legs and face.

B. Erysipelas is caused almost exclusively by

beta-hemolytic streptococcus and thus can be treated with oral or intravenous penicillin, or this infection may be treated the same as cellulitis. Adjunctive treatment and complications are the same as for cellulitis.

III. Impetigo

A. Impetigo is most commonly seen in children aged

two to five years and is classified as bullous or nonbullous. The nonbullous type predominates and presents with an erosion (sore), cluster of erosions, or small vesicles or pustules that have a honey-yellow crust. Impetigo usually appears in areas where there is a break in the skin, such as a wound, herpes simplex infection, or angular cheilitis.

B. The bullous form of impetigo presents as a large

thin-walled bulla (2 to 5 cm) containing serous yellow fluid. It often ruptures leaving a denuded area. Both forms of impetigo are primarily caused by S. aureus with Streptococcus usually being involved in the nonbullous form.

C. An oral antibiotic with activity against S. aureus

and group A beta-hemolytic streptococcus is warranted in nonlocalized cases.

1. Azithromycin (Zithromax) for five days and

cephalexin (Keflex) for 10 days have been shown to be effective and well-tolerated.

2. Dicloxacillin (Pathocil), 500 mg PO qid for 2

weeks.

3. Oxacillin (Prostaphlin) 1-2 gm IV q4-6h. 4. Cephalexin (Keflex) 250-500 mg PO qid. 5. Amoxicillin/clavulanate (Augmentin) 500 mg tid

or 875 mg bid for 7-10 days.

6. Broad-spectrum fluoroquinolones have also

been shown to be effective for treating skin and soft tissue infections. These medications have excellent skin penetration and good

bioavailability.

IV.Folliculitis

A. The most common form is superficial folliculitis that

manifests as a tender or painless pustule that heals without scarring. Multiple or single lesions can appear on any skin bearing hair including the head, neck, trunk, buttocks, and extremities. S. aureus is the most likely pathogen. Topical therapy with erythromycin, clindamycin (Cleocin T gel), mupirocin (Bactroban), or benzoyl peroxide can be administered to accelerate the healing process.

B. Staphylococci will occasionally invade the deeper

portion of the follicle, causing swelling and ery- thema. These lesions are painful and may scar. This inflammation of the entire follicle or the deeper portion of the hair follicle is called deep folliculitis. Oral antibiotics are usually used and include first-generation cephalosporins, penicillinase-resistant penicillins, macrolides, and fluoroquinolones.

C. Gram-negative folliculitis usually involves the face

and affects patients with a history of long-term antibiotic therapy for acne. Pathogens include Klebsiella, Enterobacter, and Proteus species. It can be treated as severe acne with isotretinoin (Accutane).

V. Furuncles and Carbuncles

A. Furuncles and carbuncles occur as a follicular

infection progresses deeper and extends out from the follicle. Commonly known as an abscess or boil, a furuncle is a tender, erythematous, firm or fluctuant mass of walled-off purulent material, arising from the hair follicle. The pathogen is usually S. aureus. Typically, the furuncle will develop into a fluctuant mass and eventually open to the skin surface.

B. Carbuncles are an aggregate of infected hair

follicles that form broad, swollen, erythematous, deep, and painful masses that usually open and drain through multiple tracts. Fever and malaise, are commonly associated with these lesions. With both of these lesions, gentle incision and drainage is indicated when lesions “point” (fluctuant). The wound may be packed (usually with iodoform gauze) to encourage further drainage. In severe cases, parenteral antibiotics such as cloxacillin (Tegopen), or a first-generation cephalosporin, such as cefazolin (Ancef), are required. References, see page 282.

Psoriasis

Psoriasis affects about 2 percent of the U.S. population.

I. Diagnosis

A. Psoriasis is characterized by well-demarcated

erythematous plaques with a silvery scale. Psoria- sis is symmetrically distributed, with lesions on the ears, elbows, knees, umbilicus, gluteal cleft and genitalia. The joints, nails and scalp may also be affected. Itching is the most common symptom.

B. Guttate psoriasis is characterized by numerous

small, oval (teardrop-shaped) lesions that develop after an acute upper respiratory tract infection. Guttate psoriasis must be differentiated from pityriasis rosea, another condition characterized by the sudden outbreak of red scaly lesions. Com- pared with pityriasis rosea, psoriatic lesions are thicker and scalier, and the lesions are not usually distributed along skin creases.

Types of Psoriasis, Associated Findings and Treatment Options Type of psoriasis Clinical features Differential diagnosis Treatment options Plaque-typ

e psoriasis Red, thick,scaly le- sions with silvery scale Atopic der- matitis, irri- tant dermati- tis, cutane- ous T-cell lymphoma, pityriasis rubra pilaris, seborrheic dermatitis Localized: topical ther- apy with cort- icosteroids, calcipotriene (Dovonex), coal tars, anthralin (Anthra-Derm) or tazarotene (Tazorac). Generalized: phototherapy, systemic agents, com- bination ther- apy

Type of

psoriasis Clinicalfeatures Differentialdiagnosis Treatmentoptions

Guttate psoriasis Teardrop-sh aped, pink to salmon, scaly plaques; usually on the trunk, with sparing of palms and soles Pityriasis rosea, sec- ondary syphilis, drug erup- tion Ultraviolet B phototherapy, natural sun- light Pustular psoriasis, localized Erythemato us papules or plaques studded with pus- tules; usu- ally on palms or soles (palmoplant ar pustular psoriasis) Pustular drug erup- tion, dyshidrotic eczema, subcorneal pustular dermatosis Same as for plaque-type psoriasis Pustular psoriasis, general- ized Same as localized with a more general in- volvement; may be as- sociated with sys- temic symp- toms such as fever, malaise and diarrhea Pustular drug erup- tion, subcorneal pustular dermatosis Systemic ther- apy and/or hospitalization usually re- quired Erythroder mic psoria- sis Severe, in- tense, gen- eralized ery- thema and scaling cov- ering entire body; often associated with sys- temic symp- toms; may or may not have had preexisting psoriasis Drug erup- tion, eczem- atous der- matitis, mycosis fungoides, pityriasis rubra pilaris Systemic ther- apy and/or hospitalization usually re- quired

II. Topical Therapy

A. Treatment of Localized Psoriasis 1. Topical Corticosteroids

a. Topical corticosteroids are the most com-

monly prescribed treatment for psoriasis. Treatment is initiated with a me- dium-strength agent, and high-potency agents are reserved for thick plaques.

b. Side effects from corticosteroids may in-

clude cutaneous atrophy, telangiectasia, striae, acne, glaucoma, hypothalamus-pit- uitary-adrenal axis suppression and growth retardation. Topical calcipotriene is often used in combination with topical cortico- steroids.

2. Calcipotriene

a. Calcipotriene is a vitamin D3 analog. It

inhibits epidermal cell proliferation. Effects may not be noticeable for up to six to eight weeks.

b. Maximal benefits are achieved when

calcipotriene is used in combination with potent topical corticosteroids. Treatment could be initiated with twice-daily applica- tions of a topical corticosteroid and calcipotriene until the lesions are flat.

3. Coal Tar. Coal tar is a black viscous fluid

thought to suppress epidermal DNA synthesis. Coal tar is available as an ointment, cream, lotion, shampoo, bath oil and soap. Coal tar is effective when it is combined with topical corticosteroids.

4. Anthralin

a. If good control of psoriasis is not achieved

with topical corticosteroids, consideration should be given to the addition of anthralin or tazarotene therapy.

b. Anthralin is available in 0.1 percent to 1

percent ointments, creams and solutions. Anthralin can be combined with ultraviolet phototherapy.

5. Tazarotene is a topical retinoid, which helps to

normalize the proliferation of keratinocytes. Once-daily application of tazarotene gel, 0.05 percent or 0.1 percent concentration, has been shown to be effective.

nation with corticosteroids.

6. Sunlight and Tanning-Bed Treatment. Sun

exposure in addition to topical therapy may be beneficial when multiple areas are affected with psoriasis.

7. Intralesional Injections, Phototherapy and Systemic Therapy

a. Psoriatic plaques that fail to respond to

topical therapy may be improved by triamcin- olone (Kenalog) injected directly into the dermis. The concentration is generally 3 to 10 mg per mL.

b. The patient with refractory lesions may bene-

fit from phototherapy and systemic therapy with oral retinoids, methotrexate or cyclosporine.

c. Alefacept (Amevive), the first biologic agent

for treatment of psoriasis, is fairly effective in moderate to severe disease. Alefacept must be given parenterally (once a week). References, see page 282.