Skin Disorders Guide

A lesion is a general term for a single, small area of skin disease. Lesions may be solitary or multiple. Terms used to describe these lesions include macules, patches, papules, plaques, nodules, vesicles, pustules, bullae, erosions, and ulcers. Some authorities divide these lesions into primary and secondary types.

Rash

The term rash is collectively used to describe the presence of many lesions. The lesions comprising a rash may be isolated or at least partially confluent. The term eruption is, for practical purposes, a synonym.

Macule

A macule is an area of color change 1.5 cm or less in diameter. Such a lesion has no significant substance on palpation. For this reason, macules are never perceptibly elevated, though they may be slightly depressed. Such depressed lesions are called atrophic macules.

Patch

A patch is a nonpalpable area of color change larger than 1.5 cm in diameter. Patches otherwise have the same attributes as macules. Patches may arise as such, develop through enlargement of a single macule, or evolve via the confluent growth of several adjacent macules.

Papule

A papule is a small palpable lesion 1.5 cm or less in diameter. Papules are often elevated, but by definition, elevation is not required. Some papules exist deep in the skin where they are clearly palpable but are not visibly elevated above the level of the surrounding skin. A wheal is a papule in which the substance of the lesion consists entirely of interstitial nonloculated fluid. Wheals are often colloquially called hives.

Plaque

A plaque is a flat-topped, palpable lesion larger than 1.5 cm in diameter. It can be envisioned as a papule that has enlarged in two dimensions: length and width. Most plaques are elevated, but as for papules, those situated deep within the skin may appear even with or even depressed below the level of the surrounding skin. Plaques may arise as such, develop through planar enlargement of a single papule, or evolve through confluent growth of several adjacent papules.

Nodule

A nodule is a papule spherically enlarged in three dimensions- length, width, and depth. Nodules are usually1.5 cm or more in diameter. A cyst is a nodule with a central cavity. The term tumor, because of its connotation as a neoplasm, should be avoided as a synonym for nodule.

Vesicle

A vesicle is a fluid-filled papule in which the fluid is macroscopically loculated. In short, a vesicle is a small blister and, by definition, has a diameter of 1.5 cm or less. The fluid contained within a vesicle is initially clear, but with aging, the fluid often becomes slightly cloudy. When a vesicle roof is punctured, fluid runs out and the blister compartment collapses. Vesicles can be contrasted with wheals. Puncture of a wheal results in the appearance of a drop of fluid, but there is otherwise no flattening of the lesion. Histologically, the loculation site of a vesicle occurs either at the dermal-epidermal junction (a subepidermal blister) or within the epidermis (an intraepidermal blister).

A pustule is a vesicle that contains numerous neutrophils. Pustules should be dillerentiated from cloudy vesicles. Pustules are white or yellow-white from their inception, whereas vesicles, which are clear in the beginning, become cloudy (but never truly white) as they accumulate leukocytes in the process of aging. Pustules should not necessarily infer the presence of infection. Sterile pustules, of which there are many types, are identical in appearance to pustules of an infectious etiology. Small white papules, such as milia, that are filled with keratin may resemble pustules, but they are solid on palpation and lack fluid when punctured. A hemorrhagic vesicle contains erythrocytes and therefore is red, blue, or black.

Vesicles of all types are fragile. When the roof of a vesicle is damaged or absent, the presenting lesion is a shallow erosion rather than an intact blister. The derivation of such an erosion from a preceding blister is suggested by a perfectly round shape and the presence of a peripheral collareue of scale, representing fragments of the remaining, devitalized blister roof.

Bulla

A bulla is a vesicle larger than 1.5 cm in diameter. Bullae that alise as single large blisters are unilocular and round. Bullae that develop through the coalescence of multiple small vesicles are usually multilocular and often irregular in configuration.

Erosion

An erosion occurs when a lesion Jacks overlying epithelium. Since the epithelial layer is thin, an erosion is visibly quite shallow. Depending on the rate at which fluid escapes, either an erosion will have a moist red base, or the base will be covered with crust. Erosions form as a result of two mechanisms: the spontaneous breakdown of an overlying blister roof or the disruption of nonvesicular epithelium as caused by a traumatic event. Erosions that occur secondly to blister roof breakdown are round and usually have a collarette of scale, representing remaining roof fragments encircling the periphery of the erosion. Erosions that develop as a result of external trauma (such as excoriation) are generally linear or angular in shape and lack the peripheral collarette. Erosions are encountered in vesiculobullous (group 1) and eczematous (group 10) diseases.

A fissure is a very thin, linear erosion that develops as a result of excessive drying (xerosis) of the epithelium. Fissures may have either a noninflammatory base (chapping) or a red inflammatory base (xerotic eczema).

Ulcer

An ulcer is a cutaneous defect deeper than an erosion. Not only is surface epithelium missing, but there is also a varying degree of dermal destruction. An ulcer may have a moist red base, but crust is usually present. Often, the crust is black and adherent as a result of the presence of erythrocytes and fibrin. Ulcers do not alise as a result of the unroofing of blisters. They generally occur when vascular flow to the skin is impaired. This impairment may be due to vessel compression (decubitlls ulcers), narrowing of the lumen (vasculitis, thrombosis, or embolism), or tissue growth outstripping its blood supply (ulceration of tumors). Ulcers generally occur in diseases classified with the skin-colored nodules (group 3) or the vascular reactions (group 8).