• Clinical science

Principles of dermatology

Abstract

Dermatology is the branch of medicine concerned with the skin, hair, and nails, as well as the conditions associated with them. Basic knowledge of dermatology is essential for every physician, as approximately 50% of skin-related consultations are initially assessed by non-dermatologists. In the United States, the most common conditions seen by dermatologists include acne, actinic keratoses, non-melanoma skin cancers, benign tumors, and contact dermatitis. Skin lesions may be primary or secondary. Primary lesions (e.g., macules or papules) appear as a direct result of a disease process. Secondary lesions such as scales or ulcers may develop from primary lesions or result from external trauma (e.g., infections, scratching). Dermatological conditions can often be diagnosed based on patient history and physical examination but may require laboratory testing or biopsy to confirm the diagnosis. Dermatological diseases are managed with medication (topical and systemic) and procedures such as surgery, cryotherapy, radiotherapy, or phototherapy. Topical treatments are often the first choice because they cause fewer systemic side effects and are easily administered.

Patient history

  • Chief complaint
  • Seek to address the patient's main concern by beginning with an open-ended question.
  • History of present illness
    • Onset and duration
    • Morphology and type of lesions
    • Symptoms
  • Past medical history
    • Underlying diseases may be responsible for skin findings (e.g., erythema nodosum in chronic bowel disease).
  • Drug history
    • Drug interactions may lead to skin irritations. Therefore, it is important to note any changes in the patient's drug regimen.
  • Review of systems
    • Diseases such as diabetes, rheumatic diseases, infections, and endocrine disorders (hyperthyroidism) may lead to skin conditions.
  • Family history
    • "Café au lait" spots in young children may be part of an inherited disease such as neurofibromatosis.
    • Taking a family history of skin diseases helps to determine the correct diagnosis.
      • For example, if a family history of atopic disease is noted, a child experiencing chronic itching in the antecubital and popliteal fossae can be more easily diagnosed with atopic dermatitis.
  • Social history
    • Certain skin conditions may be due to work-related chemical exposure.
    • In patients with genital ulcers, sexual history must be taken into account. Sexual partners may need to be treated as well.
    • A complete skin exposure history may be necessary for patients with contact dermatitis,

Physical examination

  • Physical examination
  • Definition of lesions (primary/secondary lesions)
  • Description of lesions
    • Number (single/multiple)
    • Size
    • Color (e.g., pinkish discoloration in cutis marmorata)
    • Texture (e.g., atrophic, calloused, crusty, verrucous)
    • Shape (e.g., round, oval, annular)
    • Distribution
      • Symmetric/asymmetric
      • Unilateral/bilateral
      • Diffuse/grouped
  • Basic examination techniques
    • Palpation: evaluation of consistency (e.g., softness, firmness) and depth
    • Typical signs
    • Dermatoscope inspection
  • Diagnostic methods
    • Biopsy (histological examination of lesions)
    • Laboratory studies

The mouth, scalp, and nails should not be overlooked!

References:[1]

Primary lesions

Primary Lesion Description

Macule

  • A flat skin lesion differing in color from the surrounding skin
Papule
  • A small, palpable skin lesion < 1 cm in diameter
Nodule
  • An elevated lesion, > 1 cm in both diameter and depth
Plaque (dermatology)
  • Palpable, usually raised lesion > 1 cm
Vesicle
  • Small fluid-containing blister < 1 cm in diameter
Bulla
  • Large fluid-containing blister > 1 cm in diameter
Urticaria (hives)
  • Sharply demarcated lesions on edematous skin
  • Irregular borders
  • Transient (hours to days)
Pustule

References:[2][3]

Secondary lesions

Secondary Lesions Description
Scale
  • Thickened stratum corneum
  • Scales are dry and usually whitish.
  • In contrast, crust is often moist and yellowish or brown.
Crust
  • Liquid debris (e.g., dried pus or blood)
Fissure (crack, cleft)
Ulcer
  • Rounded or irregularly shaped deeper lesions that result from loss of the epidermis and some portion of the dermis.
Erosion
Excoriation (scratch marks)
  • Abrasion produced by mechanical force, usually involving the epidermis (but sometimes reaching the outer layer of the dermis)
Necrosis
  • Dead skin tissue
Skin atrophy
Scar
  • Composed of new connective tissue that has replaced lost substance
  • An overgrowth of scar tissue manifests as keloid (thickened, raised tissue that grows beyond the borders of the scar and shows no regression).

References:[2][3]

Complex lesions

Lesions Description

Hemorrhage

Hematoma

  • Caused by bleeding into subcutaneous tissue, muscle, organ tissue or a cavity
    • Immediately after trauma: red
    • After 24–96 h: dark red; purple; blue/black
    • After 4–7 days: dark green
    • After 7 days: yellow; brownish
Subtypes of hematomas = purpura Nonpalpable purpura

Petechiae

Ecchymosis
  • Flat, red-purple, larger form of petechiae, > 5 mm in size
Palpable purpura
  • Raised, red-purple lesions
Rashes Exanthem
  • Extended uniform rash (localized or generalized)
Enanthem
  • Rash confined to the mucous membranes
Erythema
  • Reddening of the skin as a result of vasodilation (blanches if pressure is applied)
Erythroderma
  • Generalized reddening of the skin
Further lesions Lichenification
  • Thickening of the skin with accentuated skin markings
Eczema

References:[4][5][6][7]

Dermatopathology

Histopathologic finding Characteristics Examples
Acantholysis
Acanthosis
  • Acanthosis nigricans
Hypergranulosis
Hyperkeratosis
Parakeratosis
Spongiosis

Dermatologic therapy

Treatment options

The external nature of the skin allows a variety of treatment options, including:

  • Systemic medications
  • Topical medications
  • Physical procedures

Types of topical preparations

Drugs must be absorbed into the skin to be effective. Therefore, choosing the proper type of topical preparation for the pharmacological agent is important. Examples include:

  • Creams
  • Ointments
  • Lotions, foams, and gels

Topical steroids

Topical steroids are the most frequently used topical treatment in dermatology.

  • Advantages
    • High therapeutic value
    • Relatively safe: few local and systemic adverse effects
  • Most common side effects:
  • Common examples:
Agent Potency Indication
Hydrocortisone (1%) Low For mild and chronic dermatoses and for use on the face
Triamcinolone (0.1%) Medium For intermediate severity
Clobetasol (0.05%) High For more severe dermatoses

References:[8][9]