Scales are dry or greasy masses of keratin that represent thickened stratum corneum.
Characteristic types of scales are:
- Silvery-white scales: psoriasis
- Greasy/waxy, yellowish scales: seborrheic dermatitis
- Dry, diffuse, and fish-like scales on lower legs (ichthyosiform): ichthyosis vulgaris
- Fine scales: tinea versicolor
- Scaling in sheets: scarlet fever
- Follicular scales (such as keratotic plugs): keratosis pilaris
- Gritty (sandpaper-like) scales: actinic keratosis
- Dried exudate of body fluids (blood, pus, or sebum) on an area of damaged skin
- The color of the crust gives clues to its cause:
- Yellow crusts arise from sebum.
- Yellow-green crusts are formed from pus.
- Red or brown crusts are formed from blood (hemorrhagic crust).
- Shape may indicate previous lesion:
- Round/oval: former vesicle/bulla or pustule
- Linear: excoriations
- May be thin, delicate, and easy to remove or thick and deeply attached to the skin.
- Examples include:
- Tinea capitis
- Scabs on healing wounds
- Discontinuity of the skin exhibiting incomplete loss of the epidermis
- Does not penetrate below the dermal–epidermal junction and, thus, heals without scarring
- Lesion is moist, well-circumscribed, and depressed.
- Can be traumatic, inflammatory, or due to infectious skin diseases
- Examples include:
- Tinea pedis
- Eczematous disease
- Herpes simplex
Excoriation is a linear abrasion produced by mechanical means (scratching, rubbing, or picking) that usually involves only the epidermis but can reach the papillary dermis.
- A breakdown of the skin exhibiting complete loss of the epidermis and often portions of the dermis and subcutaneous fat
- Ulcers always result in a scar.
- Causes include:
- Trauma (e.g., heat, cold, electrical, chemical)
- Infections (e.g., bacterial, viral, fungal)
- Chronic venous stasis
- Vascular compromise (e.g., decubitus ulcers and peripheral arterial disease)
- A linear crack in the skin that is usually narrow and extends through the epidermis into the dermis
- Caused by external tension or excessive drying of the skin
- Fissures commonly occur at the angles of the mouth (angular cheilitis).
- Examples also include eczema (fingertips) and intertrigo.
- A loss of tissue that can be epidermal, dermal, or subcutaneous
- Atrophic skin usually appears thin, translucent, and wrinkled.
- Produced by long-term sun exposure, aging, and some inflammatory and neoplastic skin diseases, such as systemic lupus erythematosus and cutaneous T-cell lymphoma
- Atrophy also may occur as a result of the long-term use of topical corticosteroids.
- Thickening and hyperpigmentation of the skin resulting from repeated rubbing
- Normal skin/skinfold markings become more prominent.
- Examples include:
- Lichen simplex chronicus
- Atopic dermatitis
Approach to Diagnosing Skin Conditions
Complete medical history
- Underlying conditions (e.g., autoimmune disorders, diabetes)
- Accompanying symptoms (e.g., burning, itching)
- Evolution and duration of skin lesion, aggravating and alleviating factors
- Social, sexual, and travel history
A general physical examination as well as a focused dermatologic examination should be performed:
- Skin and its appendages as well as mucous membranes
- Performed with the naked eye and using a dermatoscope
Skin features and commonly associated skin conditions and/or lesions to consider:
- Raised: papule, plaque, nodule, cyst, wheal
- Depressed: ulcer, atrophy
- Flat: macule, patch
- Fluid-filled: vesicle, bulla, furuncle, pustule, abscess
- Dome-shaped: hemangioma
- Flat-topped: verruca plana
- Umbilicated: molluscum contagiosum
- Accuminate: condylomata acuminata
- Verrucous: verruca vulgaris
- Pedunculated: acrochordon (skin tag)
- Diameter: varies per condition
- Composition: fluid-filled, pus-filled, blood-filled, or solid
- Borders: regular or irregular, flat or raised
- Color: hypopigmentation, hyperpigmentation, or erythema
- Arrangement: grouped (herpetiform)/scattered
- Annular: tinea corporis, granuloma annulare
- Round/discoid/nummular: eczema, discoid lupus
- Polycyclic: urticaria
- Arcuate: urticaria
- Linear: scabies burrow, lichen nitidus
- Reticular: livedo reticularis
- Serpiginous: cutaneous larva migrans
- Targetoid lesions: erythema multiforme
- Whorled: incontinentia pigmenti
- Skin biopsy (lesion excised, saucerized, or taken by punch biopsy)
- KOH preparation:
- Lesion is scraped and placed on a glass microscope slide, where it is treated with 1 or 2 drops of a solution of 10%–20% KOH.
- If fungal infection suspected
- Tzanck smear: cytologic technique when vesicular conditions are noted (infections from herpes simplex virus or varicella zoster virus).
- Diascopy: determines whether lesion will blanch under pressure, differentiating a hemorrhagic (does not blanch) from a fluid-filled lesion
- Wood’s light:
- Uses 360-nm UV light to evaluate lesions
- Conditions: erythrasma (coral pink color), Pseudomonas wound infection (blue), vitiligo (white)
- Patch test: allergens placed on patient’s back under occlusive dressings and then checked for hypersensitivity reactions after 48 hours
- Amerson, E. H., Burgin, S., Shinkai, K. (2019). Fundamentals of clinical dermatology: morphology and special clinical considerations. In Kang, S., et al. (Eds.). Fitzpatrick’s Dermatology, 9th ed. McGraw-Hill.
- Bolognia, J. L., Schaffer, J.V ., Cerroni, L. (2018). Basic Principles of Dermatology, 4th ed. Edinburgh. Elsevier.