Atlas of pathophysiology, 2 Edition

Part II - Disorders

Skin Disorders

Cellulitis

Cellulitis is an acute, spreading infection of the dermis or subcutaneous layer of the skin. It may follow damage to the skin, such as a bite or wound. As the cellulitis spreads, fever, erythema, and lymphangitis may occur. Persons with contributing health problems, such as diabetes, immunodeficiency, or impaired circulation, have an increased risk. If treated promptly, the prognosis is usually good.

Age Alert

Cellulitis of the lower extremity is more likely to develop into thrombophlebitis in an elderly patient. Orbital cellulitis, especially in children, may require hospitalization and I.V. antibiotics because of the increased risk of spread to intracranial structures, such as in thin bones and numerous openings in the bone.

Causes

·   Bacterial infections, commonly with group A beta-hemolytic streptococcus or Staphylococcus aureus

·   In patients with diabetes or decreased immune function: Escherichia coli, Proteus mirabilis, Acinetobacter, Enterobacter, Pseudomonas aeruginosa, Pasteurella multocida, Vibrio vulnificus, Mycobacterium fortuitum complex, and Cryptococcus neoformans

·   In children, less commonly caused by pneumococci and Neisseria meningitidis group B (periorbital)

Pathophysiology

After the organisms enter the tissue spaces and planes of cleavage, hyaluronidases break down the ground substances composed of polysaccharides while fibrinolysins digest fibrin barriers and lecithinases destroy cell membranes. This overwhelms the normal cells of defense (neutrophils, eosinophils, basophils, and mast cells) that normally contain and localize inflammation, and cellular debris accumulates.

Signs and symptoms

·   Classic signs: erythema and edema due to inflammatory response, usually well-demarcated

·   Pain at site and possibly in surrounding area

·   Fever and warmth

·   Regional lymphadenopathy or lymphangitis

Diagnostic test results

·   White blood cell count shows mild leukocytosis with a shift to the left.

·   Erythrocyte sedimentation rate is mildly elevated.

·   Culture and gram stain results of fluid from abscesses and bulla are positive for the offending organism.

·   Using the “Touch” preparation, potassium hydroxide is applied to a microscope slide containing a skin lesion specimen that detects the presence of yeast or mycelial forms of fungus.

Treatment

·   Oral or I.V. penicillin (drug of choice for initial treatment) unless patient has known penicillin allergy; antifungal medications if needed

·   Alternative antibiotics based on culture and sensitivity results

·   Warm soaks to the site to help relieve pain and decrease edema by increasing vasodilation

·   Pain medication as needed

·   Elevation of infected extremity

·   Surgical drainage or debridement

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PHASES OF ACUTE INFLAMMATORY RESPONSE

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Clinical Tip

Recognizing Cellulitis

The classic signs of cellulitis, a spreading soft tissue infection, are erythema and edema surrounding the initial wound. The tissue is warm to the touch.

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