Morphology of Primary and Secondary Skin Lesions

1

Why do dermatologists use words that no one else understands?

The language of dermatology is unique. It encompasses terms that rarely, if ever, are used in other medical specialties. The use of these correct dermatologic terms is important to accurately describe skin lesions to dermatologists during telephone calls and during rounds and teaching. A good description of a skin lesion enables the listener to formulate a series of differential diagnoses, whereas a poor one does not.

2

But why are the descriptions so long?

Use of appropriate terminology and important clues, such as configuration and skin distribution, effectively paints an accurate picture for the listener. Use of vague terms—spot, bump, rash, and lesion—is not helpful. Such vocabulary is counterproductive to formulating an accurate differential diagnosis. “Grouped vesicles on an erythematous base” immediately suggests herpes simplex, and “brown, friable ‘stuck-on’ papules” accurately describes seborrheic keratoses. “Well-demarcated, erythematous plaques with micaceous, silvery scales located on extensor surfaces” is suggestive of psoriasis. “Violaceous, polygonal papules with Wickham's striae located on flexural surfaces” is consistent with lichen planus. On the other hand, “red, scaly rash on the foot” describes an enormous, nebulous group of disorders.

3

How can I possibly learn the language of dermatology?

First, learn the definitions of the various primary, secondary, and special skin lesions. Each of these groups consists of a short list of terms that specifies basic types. Then, follow this simple template when describing skin lesions:

• Size

• Color or additional descriptive terms (e.g., pigmentation, shape)

• Type of primary, secondary, or special skin lesion (e.g., papule, macule)

• Arrangement (e.g., grouped lesions)

• Distribution (e.g., truncal, generalized). This template provides a systematic way to add adjectives to the type of lesion. Repetition is key; practice using the template when describing skin lesions.

4

What is a primary skin lesion?

It is the initial lesion that has not been altered by trauma, manipulation (scratching, scrubbing), or natural regression over time. Examples include:

• Macules

• Wheals

• Papules

• Vesicles

• Plaques

• Bullae

• Patches

• Pustules

• Nodules

• Cysts

5

How is each of the primary lesions defined?

See Table 2.1 .

Table 2.1

Primary skin lesions

Primary Lesion	Definition	Morphology	Examples
Macule	Flat, circumscribed skin discoloration that lacks surface elevation or depression		Café-au-lait Vitiligo Freckle Junctional nevi Ink tattoo
Papule	Elevated, solid lesion < 0.5 cm in diameter		Acrochordon (skin tag) Basal cell carcinoma Molluscum contagiosum
Plaque	Elevated, solid “confluence of papules” (> 0.5 cm in diameter) that lacks a deep component		Bowen's disease Mycosis fungoides Psoriasis Eczema Tinea corporis
Patch	Flat, circumscribed skin discoloration; a very large macule		Port wine stain Vitiligo
Nodule	Elevated, solid lesion > 0.5 cm in diameter; a larger, deeper papule		Rheumatoid nodule Tendon xanthoma Erythema nodosum Lipoma Metastatic carcinoma
Wheal	Firm, edematous plaque that is evanescent and pruritic; a hive		Urticaria Dermographism Urticaria pigmentosa
Vesicle	Papule that contains clear fluid; a blister		Herpes simplex Herpes zoster Vesicular hand dermatitis Contact dermatitis
Bulla	Localized fluid collection > 0.5 cm in diameter; a large vesicle		Pemphigus vulgaris Bullous pemphigoid Bullous impetigo
Pustule	Papule that contains purulent material		Folliculitis Impetigo Acne Pustular psoriasis
Cyst	Nodule that contains fluid or semisolid material		Acne Epidermal inclusion Trichilemmal cyst

6

How do you determine whether a lesion is flat or raised?

Palpation is the most reliable method, but side-lighting also helps. It can be difficult to distinguish a macule from a papule or a patch from a plaque in a photograph, and it is one of the limiting factors in teledermatology.

7

How does a primary lesion differ from a secondary lesion?

Secondary skin lesions are created by scratching, scrubbing, or infection. They may also develop normally with time. For example, the primary lesion in a sunburn is a macular erythema (although it could also be a blister), but with resolution, scale and increased pigmentation become prominent. Examples of secondary lesions include:

• Crusts

• Scale

• Ulcers

• Fissures

• Excoriations

• Scars

• Erosions

• Postinflammatory dyspigmentation