Macule
- A flat, non-palpable skin lesion measuring ≤ 1 cm in size
- Differs in color from surrounding skin (hypopigmented/hyperpigmented or erythematous)
- Not raised or depressed compared to the skin surface
- Examples:
- Freckles
- Moles
- Café-au-lait macules
- Macules in rubella
- Macules in measles
Patch
- A flat skin lesion measuring > 1 cm in size
- Differs in color from the surrounding skin
- Nonpalpable and larger than a macule
- Examples include vitiligo and melasma.
A patch of vitiligo in a person with dark skin
Image: “Vitiligo and the melanocyte reservoir” by Falabella, R. License: CC BY 2.0
Hyperpigmentation on the cheek of a patient with melasma
Image: “A study comparing chemical peeling using modified Jessner’s solution and 15% trichloroacetic acid versus 15% trichloroacetic acid in the treatment of melasma” by Safoury OS, Zaki NM, El Nabarawy EA, Farag EA. License: CC BY 2.0
Papule
- A raised, palpable skin lesion measuring ≤ 1 cm in diameter
- The color can indicate the diagnosis:
- Brown or black papules are often melanocytic lesions.
- Red papules are often vascular lesions.
- Examples:
- Nevi
- Warts
- Lichen planus
- Insect bites
- Seborrheic keratoses
- Molluscum contagiosum
- Angiomas
- Skin cancers
Plaque
- Raised skin lesion measuring > 1 cm in diameter
- Usually have palpable surface change as lesion arises from the epidermis
- May have a flat-topped or rounded appearance.
- Examples:
- Psoriasis
- Granuloma annulare
- Seborrheic dermatitis
- Eczema
Severe plaque psoriasis
Image: “Psoriasis manum” by George Henry Fox. License: Public DomainNodule
- A large, firm lesion raised above the surface of the surrounding skin and measuring 1–5 cm
- Usually extends into the dermis and subcutaneous tissue
- The surface may be smooth, keratotic, ulcerated, or fungating.
- Examples:
- Neurofibromas
- Cysts
- Lipomas
Vesicle
- A small, fluid-containing blister (collection of fluid in the skin) measuring ≤ 1 cm in diameter
- Raised above the plane of the surrounding skin
- The fluid is visible as the lesions are translucent.
- Observed in:
- Chickenpox
- Herpes zoster
- Impetigo
- Dermatitis herpetiformis
Bulla
- A large, clear fluid-containing blister measuring > 1 cm in diameter
- May be caused by:
- Burns
- Bites
- Irritant/allergic contact dermatitis
- Drug reactions
- Classic autoimmune bullous diseases include pemphigus vulgaris and bullous pemphigoid.
Urticaria (Wheals or Hives)
- Sharply demarcated and elevated lesions with irregular borders:
- Usually erythematous and may have central pallor
- Formed due to sudden extravasation of fluid into the dermis
- Wheals are pruritic and ALWAYS disappear within 24 hours.
- Can be caused by:
- Medication hypersensitivity
- Insect stings or bites
- Autoimmune conditions
- Physical stimuli (e.g., temperature, pressure, sunlight)
Pustule
- A vesicle filled with pus
- Formed due to the collection of inflammatory exudate that is rich in leukocytes
- May contain bacteria or may be sterile
- Pustules are common in:
- Folliculitis
- Pustular psoriasis
- Scabies
- Acne
Bacterial folliculitis on the lower leg presenting as follicular pustules
Image: “Folliculitis on lower leg” by Da pacem Domine. License: Public DomainTelangiectasia
- Also known as “spider veins“
- Appear as fine, bright red lines or a net-like pattern
- Represent a dilation of capillaries that blanch upon pressure
- Not elevated and are often found on the face, trunk, and around the nail bed
- Telangiectasias occur in:
- CREST (calcinosis, Raynaud’s phenomenon, esophageal dysmotility, sclerodactyly, and telangiectasia) syndrome
- Dermatomyositis
- Systemic sclerosis
- Ataxia telangiectasia
- Skin cancers
Petechiae
- Punctate foci of hemorrhage (seen as small red, purple, or brown spots) measuring < 3 mm in size
- Petechiae are seen in the setting of:
- Thrombocytopenia
- Platelet dysfunction
- Vasculitis
- Infections (e.g., meningococcemia, Rocky Mountain spotted fever)
Petechiae around intravenous site
Image by Jeremy Greer, MD (Lecturio).Purpura
- Extravasation of RBCs from cutaneous vessels in the skin and mucous membranes:
- Usually palpable and non-blanching with diascopy
- Usually red, purple, or even blue in color
- Purpura is seen in leukocytoclastic vasculitis (e.g., Henoch-Schöenlein purpura and polyarteritis nodosa).
- A large area of purpura may be called an ecchymosis.
Approach to Diagnosing Skin Conditions
Complete medical history
- Underlying conditions (e.g., autoimmune disorders, diabetes)
- Accompanying symptoms (e.g., burning, itching)
- Medications
- Allergies
- Evolution and duration of skin lesions, and aggravating and alleviating factors
- Social, sexual, and travel history
Physical examination
A general physical examination as well as a focused dermatological 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:
- Texture:
- Raised: papule, plaque, nodule, cyst, wheal
- Depressed: ulcer, atrophy
- Flat: macule, patch
- Fluid filled: vesicle, bulla, furuncle, pustule, and abscess
- Morphology:
- Dome shaped: hemangioma
- Flat topped: verruca plana
- Umbilicated: molluscum contagiosum
- Accuminate: condylomata acuminata
- Verrucous: verruca vulgaris
- Pedunculated: acrochordon (skin tag)
- Diameter: varies depending on the condition
- Composition: fluid-filled, pus-filled, blood-filled, or solid structures
- Borders: regular or irregular, flat or raised
- Color: hypopigmented, hyperpigmented, or erythema
- Arrangement: grouped (herpetiform)/scattered
- Configuration:
- 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
Different primary skin lesions:
A macule is a flat ≤ 1 cm non-palpable skin lesion.
A papule is a raised ≤ 1 cm palpable skin lesion.
A nodule is a large 1–5 cm firm raised lesion, usually extending into the dermis and subcutaneous tissue.
A plaque is a raised > 1 cm skin lesion with palpable surface change as it arises from the epidermis.
A vesicle is a small ≤ 1 cm fluid-containing blister while a bulla is a large > 1 cm clear fluid-containing blister.
Diagnostic procedures
- Skin biopsy (lesion excised, saucerized, or obtained by punch biopsy)
- KOH preparation:
- Lesion scraped and placed on a glass microscope slide, where it is treated with 1 or 2 drops of 10%–20% KOH
- If fungal infection suspected
- Tzanck smear: cytologic technique when vesicular conditions are noted (herpes simplex or varicella zoster infections)
- Diascopy: to determine if a lesion will blanch on pressure, differentiating a hemorrhagic (does not blanch) from a fluid-filled lesion
- Wood’s light:
- Utilizes 360 nm UV light to evaluate lesions
- Conditions: erythrasma (coral pink color), Pseudomonas wound infections (blue), vitiligo (white)
- Patch test: allergens placed on patient’s back under occlusive dressings and checked for hypersensitivity reactions after 48 hours.
References
- Yancey, K.B., Lawley, T.J. (2018). Approach to the patient with a skin disorder. In Jameson, J., et al. (Eds.). Harrison’s Principles of Internal Medicine, 20e. McGraw-Hill.
