Impetigo is a common, highly contagious bacterial infection affecting the superficial layer of the skin, the epidermis. Accurate physical examination is the primary method for diagnosis, relying on precise dermatologic terminology to differentiate it from other skin conditions. A detailed description of the lesions, including their morphology and distribution, is necessary for effective communication among healthcare providers and to guide appropriate treatment.
Initial Observation and Patient Status
The initial observation of a patient with impetigo usually reveals a person who is not acutely ill. The general appearance is typically non-toxic, meaning the infection is localized to the skin without signs of systemic illness. Vital signs are within normal limits, and fever is uncommon in the non-bullous form.
Patients commonly report subjective symptoms related to the skin lesions, most often pruritus, or itching. They may also describe mild tenderness or a burning sensation at the site of the infection.
Describing Non-Bullous Impetigo Lesions
Non-bullous impetigo, which is the most frequent presentation, begins with small, transient primary lesions. These lesions first appear as tiny vesicles or pustules, which are fluid-filled sacs less than one centimeter in diameter. These thin-walled vesicles rapidly rupture, often within hours, making them difficult to observe during a typical examination.
Once the primary lesion breaks open, a moist erosion is left behind, exuding a purulent, serous fluid. This exudate dries to form the characteristic secondary lesion, which is an adherent, golden-yellow or amber-colored crust. This thick crust is often described as resembling dried honey, and it sits upon a mildly erythematous, or reddened, base.
The individual crusted lesions are generally small, typically measuring less than two centimeters, and possess well-defined margins. Removal of the crust reveals the moist, underlying erosion, which may quickly re-exude fluid. New lesions, known as satellite lesions, often occur nearby as the infection is easily spread by self-inoculation.
Describing Bullous Impetigo Lesions
The bullous form of impetigo presents with a distinctly different morphology. The primary lesion is the bulla, a large blister greater than one centimeter in diameter. These bullae are typically flaccid and thin-roofed, appearing on skin that may initially be non-erythematous.
The fluid within the intact bullae is initially clear or yellowish but can progress to become cloudy or darker over time. Due to their fragile nature, the bullae rupture easily, often leaving only remnants of the blister roof visible. Following rupture, the remaining skin surface appears as a raw, moist erosion that dries to form a thin, lacquer-like, brown crust.
A specific observation upon rupture is the presence of a collarette of scale, which is a thin rim of scaling skin at the periphery of the erosion. Unlike the other subtype, bullous impetigo does not develop the thick, golden, “honey-colored” crusts. The lesions in bullous impetigo generally lack the significant surrounding redness often seen with other bacterial skin infections.
Documenting Location and Distribution
The physical examination must precisely document the anatomical location and pattern of lesion spread. Non-bullous impetigo lesions commonly appear on exposed body parts, with a strong predilection for the face, particularly around the mouth and nose. The extremities, such as the arms and legs, are also frequently affected, often starting at sites of minor skin trauma.
Lesions may be grouped or clustered together, and smaller lesions can coalesce to form larger affected areas. Spread occurs through autoinoculation, where bacteria are transferred to a new site by scratching. An associated finding, particularly with the non-bullous form, is the presence of mild regional lymphadenopathy (swelling of the lymph nodes closest to the infected area).
Bullous lesions, in contrast, often favor areas where skin surfaces rub together, known as intertriginous regions. These locations include the armpits, neck folds, trunk, and the diaper area in infants. While the non-bullous form tends to be numerous, bullous impetigo often presents with fewer lesions, and regional lymphadenopathy is typically absent in this variant.