Principles of dermatology

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 and papules) appear as a direct result of a disease process. Secondary lesions (e.g., scales and 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 confirming the diagnosis may require laboratory testing or biopsy. Dermatological diseases are managed with medication (topical and systemic) and procedures such as surgery, cryoablation, radiotherapy, or phototherapy. Conservative treatment with topical agents is the treatment of choice for most dermatological conditions, with systemic medication and/or surgery being employed only if necessary. The prevalence, manifestations, and treatment of dermatological conditions in skin of color may vary depending on skin tone and genetic inheritance.

See also “Rash” for a clinical approach to various rashes (e.g., maculopapular rash, vesiculobullous rash, petechial rash, diffuse erythematous rash) and related skin lesions (e.g., annular skin lesions).

• History of present illness
  • Establish the chief concern
  • Onset and duration
  • Morphology and type of lesions
  • Symptoms e.g.,:
    • Pruritus
    • Sensitivity to light
    • Pain
    • Fever
• Past medical history: Underlying diseases may be responsible for skin findings (e.g., erythema nodosum in chronic bowel disease).
• Drug history: Many drugs have cutaneous adverse and side effects. Be aware of potential drug interactions.
• Review of systems: e.g., diabetes, rheumatic diseases, infections, and endocrine disorders (e.g., hyperthyroidism)
• Family history: e.g., Café au lait spots in young children may be part of an inherited disease such as neurofibromatosis.
• Social history
  • Work hazards (e.g., exposure to chemicals)
  • Sexual history in genital dermatological manifestations. If an STI is diagnosed, sexual partners may also need to be informed and receive treatment.

Overview

• Complete skin assessment: Examine the skin (including the hands, mouth, and scalp) and nails for signs of dermatological conditions.
• Examination techniques
  • Inspection
  • Palpation: evaluation of consistency (e.g., softness, firmness)
  • Typical skin tests, as indicated:
    • Nikolsky sign
    • Auspitz sign
  • Dermatoscope inspection, as indicated
• Confirmation of diagnosis: may require biopsy for histopathological examination (see “Dermapathology” below) and/or laboratory studies

The hands, mouth, scalp, and nails should not be overlooked during a dermatological examination.

Skin examination

• Determine the type of lesion: See primary skin lesions, secondary skin lesions, and complex skin lesions below.
• Record lesion characteristics
  • Location
  • Number (single/multiple)
  • Size
  • Color: e.g., pink discoloration
  • Texture: e.g., atrophic, calloused, crusty, verrucous
  • Shape: e.g., round, oval, annular
  • Distribution
    • Symmetric/asymmetric
    • Unilateral/bilateral
    • Diffuse/grouped
  • Secondary changes (e.g., as a result of scratching)

Physical examination

Nail examination

• Inspect and palpate nails (fingers and toes) and look for alterations of the nails.

Alterations of the nails
Clinical findings	Clinical examples	Possible underlying disease
Nail pitting		Psoriasis
Onycholysis		Repetitive nail trauma Chronic irritant exposure Onychomycosis (fungal infection) Psoriasis Thyroid disease
Nail clubbing		Pulmonary: cystic fibrosis, bronchiectasis, bronchogenic carcinoma Cardiac: right-to-left cardiac shunt due to congenital heart disease Endocrine: thyroid acropachy in Graves disease Gastrointestinal: inflammatory bowel disease, celiac disease, cirrhosis
Koilonychia		Iron deficiency
Mees lines		Heavy metal poisoning History of chemotherapy Renal failure
Melanonychia		Benign: physiologic, trauma, drug-induced (e.g., cyclophosphamide, zidovudine, chloroquine), inflammatory (e.g., psoriasis), fungus, nevi, lentigo, nonmalignant tumors Malignant: melanoma, Bowen disease

Examination of the hands

Alterations of the hands
Clinical findings	Clinical examples	Possible underlying disease
Palmar erythema		Cirrhosis
Hyperpigmentation of the palms		Low cortisol levels
Heberden nodes		Osteoarthritis
Bouchard nodes
Symmetrical swelling of proximal and distal interphalangeal joints		Rheumatoid arthritis
Swan neck deformity
Ulnar deviation of the fingers
Gottron papules		Dermatomyositis
Dupuytren contracture		Trauma or idiopathic
Janeway lesions		Endocarditis
Osler nodes

Provocation tests

• Nikolsky sign
  • Slight mechanical pressure (by rubbing) causes the upper epidermal layer to slip away from the lower layer due to impaired adhesion between epidermal cells, leading to separation and blistering.
  • The test is positive on intact or only mildly erythematous skin.
  • May be present in pemphigus vulgaris, toxic epidermal necrolysis, staphylococcal scalded skin syndrome, and Stevens-Johnson syndrome
  • Not present in bullous pemphigoid

Tzanck test

• Microscopic examination of scrapings from the base of a lesion to look for Tzanck cells
• Tzanck cells (multinucleated giant cells) are present in:
  • Pemphigus vulgaris
  • Herpes simplex type 1 (HSV-1) infection
  • Varicella zoster virus infection (chickenpox or shingles)
  • Cytomegalovirus
• No detection of Tzanck cells in:
  • Bullous pemphigoid
  • Dermatitis herpetiformis

Treatment

• Topical medications
  • First choice of treatment for most conditions; often preferred for treating dermatological conditions because they cause fewer systemic side effects
  • Examples: antibiotics, antifungals, corticosteroids, cytotoxic agents, antipruritics, retinoids
• Systemic medications
• Procedures
  • Surgery
  • Cryoablation: application of cold (e.g., using liquid nitrogen) to destroy abnormal tissue, malignant or premalignant skin lesions.
• Other
  • Radiotherapy
  • Phototherapy

Types of topical preparations ^[5]

• Creams
• Ointments
• Lotions, foams, and gels

Topical steroids

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

• Most common side effects
  • Skin atrophy
  • Steroid acne
• Examples

Phototherapy ^[6][7][8]

Ultraviolet light is an effective treatment option for dermatological conditions because of its antiproliferative (e.g., slowing of keratinization) and antiinflammatory effects (e.g., inducing apoptosis of pathogenic T cells).

• UVA therapy
  • Indications: atopic dermatitis, scleroderma, chronic pruritus, prurigo simplex ^[9]
  • Adverse effects
    • Skin aging
    • ↑ Cancer risk
• UVB therapy
  • Indications: psoriasis, vitiligo, chronic pruritus, atopic dermatitis ^[9]
  • Adverse effects
    • Acceleration of photodamage (e.g., sunburn)
    • ↑ Cancer risk
• PUVA therapy: (psoralen plus UVA): topical or oral psoralen → ↑ skin photosensitivity → ↑ antiproliferative and antiinflammatory effects of UVA light
  • Indications: psoriasis, atopic dermatitis, vitiligo, mycosis fungoides
  • Adverse effects
    • Nausea, vomiting
    • ↑ Risk of squamous cell carcinoma

Overview

• “Skin of color” refers to skin with a higher degree of pigmentation than that traditionally associated with Northern European heritage.
  • Skin tone is a spectrum that does not necessarily correspond to the skin tones traditionally associated with race.
  • Genetic inheritance can play a more important role in the manifestation of dermatological conditions than skin tone.
  • It is important to recognize with regard to the concept of “race” still in use by the US Census Bureau that there is no foundation for a scientific concept of race as a specific genetic, phenotypical, ancestral, or ethnic trait that distinguishes all members of one population from those of another.
• Western medicine has traditionally focused on the presentation of light-skinned individuals, leading to underrepresentation in dermatological resources of cutaneous manifestations in individuals with skin of color.
• Changing demographics and increased representation of historically marginalized populations have raised awareness for the need and importance of thoroughly understanding skin of color.

Epidemiology

• The incidence and prevalence of dermatological conditions in individuals with skin of color depend to a high degree on skin tone and differ from those seen in light-skinned individuals for a variety of reasons:
  • Underrecognition due to poor dermatological training in diagnosing cutaneous conditions in individuals with skin of color.
  • Factors that are influenced by different lifestyle and cultural practices
  • Genetic inheritance

Physiology ^[24][25]

Skin color depends on the degree of pigmentation with melanin (contained in melanosomes, which are synthesized in melanocytes), other pigments (i.e., hemoglobin, oxyhemoglobin, and carotenoids), and melanocyte activity, all of which are determined by genetic heritage. For more information on melanin, see “Cells of the skin” in “Skin and skin appendage.”

• Differences in skin pigmentation are mainly due to differences in melanocytic activity.
  • More diffuse distribution and higher numbers of melanosomes and melanin → darker skin tone
  • Melanin provides protection against ultraviolet radiation but is not sufficient to prevent against sunburn and skin cancer
• Skin layer composition varies between different skin colors.
  • Stratum corneum (SC)
    • The darker the skin, the more keratinocyte cell layers and greater intercellular cohesion it will have.
    • Thickness: similar in all skin colors
    • Lipid content: is highest in individuals with Southeast and East Asian heritage, followed by those with Hispanic and African heritage
    • Barrier function (greater transepidermal fluid loss): African heritage > Hispanic heritage > Southeast and East Asian heritage
  • The greater the amount and size of fibroblasts, small collagen fibers, and macrophages, the higher the risk of keloid formation and scarring
• Skin appendages: larger sebaceous glands → increased sebum production (African heritage > Southeast and East Asian heritage > Hispanic heritage)

Clinical presentation ^[26]

• Dermatological symptoms may be subtle or have a characteristic appearance depending on skin pigmentation.

Overview of dermatological symptoms in skin of color
Symptom	Description	Clinical example(s)
Pallor	May appear gray-brown against a background with darker pigmentation or may only be apparent in certain areas less exposed to sunlight or with lighter pigmentation (e.g., palmar surfaces or mucous membranes).
Erythema	May appear purple or brown rather than pink or red when against a background with darker pigmentation
Hypopigmentation	May be more readily apparent against a background with darker pigmentation
Cyanosis	May appear as a grayish or lighter color in some patients or may only be apparent in areas less exposed to sunlight or with lighter pigmentation (e.g., palmar surfaces, mucous membranes, and nailbeds)
Jaundice	May be very subtle in darker skin tones and may be more apparent in the conjunctiva and sclera of the eye and mucous membranes (e.g., oral mucosa, palate).
Skin hemorrhages	May appear dark purple, brown, or even black against a background of darker pigmentation Early bruising may not be visible at all

• Specific conditions may appear uniquely in individuals with skin of color ^[27]

Distinguishing features of specific conditions in individuals with skin of color [27]
Condition	Description	Clinical example
Atopic dermatitis	May have more papular or follicular accentuation
Basal cell carcinoma	More commonly pigmented with a black or pearly brown appearance
Melanoma	More common on the palms, soles, and subungual surfaces (e.g., acral lentiginous melanoma).
Acne vulgaris	More likely to result in postinflammatory hyperpigmentation and in some cases scarring, including keloids.

Diagnostic considerations

• The prevalence, manifestations, and treatment of dermatological conditions may vary depending on skin tone and genetic inheritance.
• Lack of familiarity with the manifestations of dermatological conditions in individuals with skin of color may lead to a delay or failure to properly recognize, diagnose, and treat dermatological conditions in these patient groups.
• Keep the following recommendations in mind regarding patients with skin of color to ensure proper diagnosis and treatment:
  • Appreciate the diversity of skin tones and consider the characteristics of every patient's skin individually.
  • Familiarize yourself with differences in disease manifestations, epidemiology, and treatment of dermatological conditions that depend on skin color.
  • Familiarize yourself with and be sensitive to differences that depend on skin color and/or ethnicity in skincare (e.g., dandruff products), cosmetic use (e.g., skin bleaching products), and cultural practices (e.g., tattooing, hair extensions).
  • Familiarize yourself with the preferred terms for describing skin tones and those that should be avoided.
  • Raise awareness for common misconceptions regarding skin of color (e.g., that people of color do not require sunscreen, do not get sunburnt, and do not get skin cancer).
  • Perform a complete skin assessment upon initial presentation and familiarize yourself with the patient's normal skin tone to better recognize irregularities and lesions.
  • Use a patient-centered approach and be open about pertinent gaps in knowledge, involving the patient in helping to close them.
  • Be aware of the history of racism and its consequences also in health care, but refrain from making assumptions (e.g., regarding social status) based on skin color (see also “Social aspects of health care”).

Treatment considerations ^[26]

• Skin reactivity to certain therapies differs among skin types.
• The darker the skin, the greater the risk of postinflammatory hyperpigmentation and postinflammatory hypopigmentation
• Lifestyle and personal care practices (e.g., frequency of hair washing) may affect the practicality of certain therapies (e.g., treatment of seborrheic dermatitis on the scalp with a topical steroid oil applied nightly may be more practical than an antifungal shampoo for individuals who wash their hair every few weeks).