2. • Primary lesions — Primary lesions are either
the first visible lesion or involve the initial skin
changes. The terms used to describe primary
skin lesions include the following:
• Macules are nonpalpable lesions that vary in
pigmentation from the surrounding skin
• There are no elevations or depressions
18. Differential diagnosis of pustules
Acne rosacea/perioral dermatitis
Arthropod bite (fire ants)
Erythema toxicum neonatorum
Fungal or yeast infections
(especially tinea capitis and
• Vesicles are small (<5 mm
diameter), circumscribed skin papules
containing serous material
• Bullae are large (≥6 mm) vesicles.
• Multiple vesicles are present in this patient
with herpes zoster
• Wheals are irregularly elevated edematous
skin areas that are often erythematous
• The borders of a wheal are sharp but not
stable; they may move to adjacent uninvolved
areas over periods of hours
23. Secondary lesions
• Secondary lesions — Secondary lesions of the skin represent evolved changes from the skin
disorder, due to secondary manipulation or as a result of infection. Examples include:
• Excoriation describes superficial, often linear, skin erosion caused by scratching (picture 10).
• Lichenification is increased skin markings and thickening with induration secondary to chronic
inflammation caused by scratching or other irritation (picture 11).
• Edema is swelling due to accumulation of water in tissue (picture 12).
• Scale describes superficial epidermal cells that are dead and cast off from the skin (picture
• Crust is dried exudate, a "scab."
• Fissure is a deep skin split extending into the dermis.
• Erosion is a superficial, focal loss of part of the epidermis. Lesions usually heal without
scarring (picture 14). Ulceration is focal loss of the epidermis extending into the dermis.
Lesions may heal with scarring (picture 15). The differential diagnosis of erosions and ulcers is
shown in a table (table 8).
• Atrophy is decreased skin thickness due to skin thinning.
• Scar is abnormal fibrous tissue that replaces normal tissue after skin injury.
• Hypopigmentation (picture 16) is decreased skin pigment; hyperpigmentation (picture 17) is
increased skin pigment; and depigmentation (picture 18) is total loss of skin pigment.