Dermatology notes

Objectives

  • Upon completing this module, the learner should be able to:

    • Conduct a comprehensive dermatologic history, including chief complaint, history of present illness (HPI), past medical history (PMH), family history (FH), social history (SH), and review of systems (ROS).

    • Master full-body skin, hair, and nail examination techniques, ensuring identification of subtle findings and thorough assessment of all integumentary structures.

    • Contrast normal findings with expected physiological and pathological variations across different age groups (infants, children, adolescents, adults, older adults) and during pregnancy.

    • Systematically detect deviations from expected findings and accurately map them to common dermatological pathologies, understanding their underlying mechanisms.

    • Formulate a well-reasoned initial differential diagnosis (DDx) for common skin problems, prioritizing based on clinical likelihood and severity.

    • Recognize critical dermatologic red flags that signal emergent, life-threatening, or significant systemic disease, necessitating urgent referral or intervention.

    • Document history, physical exam findings, and differential diagnosis accurately and concisely using the standard SOAP (Subjective, Objective, Assessment, Plan) format.

Inclusive Dermatology – Equity Highlight

  • The 2024 NEJM “Efforts toward Equity” article prominently profiles the open-access Inclusive Dermatology Atlas, a collaborative initiative by the University of New Mexico (UNM) and East Carolina University (ECU).

    • This unique photo bank systematically spans all Fitzpatrick skin types (I–VI), offering a crucial resource for visual learning and diagnostic training.

    • The primary aim is to significantly improve diagnostic accuracy for skin conditions across diverse populations and, in turn, reduce persistent health disparities in patients with skin of color, where common dermatoses may present atypically.

    • All images are carefully de-identified and ethically consented (created from 2022 onwards), ensuring patient privacy and responsible data use.

    • This initiative directly addresses and mitigates the inherent bias present in traditional dermatology teaching images, which historically have been overwhelmingly dominant in depicting light-skinned individuals; the resource is widely available online as the Inclusive Dermatology Gallery.

  • Ethical / practical implication: direct and broad access to a diverse range of dermatological images demonstrably lowers misdiagnosis rates, particularly in darker skin tones, thus actively supporting more equitable and effective patient care by fostering more inclusive diagnostic capabilities.

Quick Anatomy & Physiology Review

  • Skin (integumentary system) is the largest organ of the body, continuously interacting with the external environment; comprised of three primary layers: Epidermis (outermost) → Dermis (middle) → Subcutaneous tissue (innermost).

  • Major functions of the skin:

    • Barrier: Provides robust protection against microbial invasions, physical trauma, chemical irritants, and crucial prevention of excessive fluid loss (dehydration).

    • Thermoregulation & Blood Pressure Modulation: Regulates body temperature via vasodilation/vasoconstriction of dermal blood vessels and evaporation of sweat via eccrine glands; influences systemic blood pressure through vasomotor tone.

    • Sensory Perception & Emotional Expression: Houses numerous nerve endings and specialized sensory receptors (e.g., touch, pressure, pain, temperature); facilitates non-verbal communication through flushing, pallor, or piloerection.

    • Vitamin D Synthesis, Immune Surveillance, & Wound Repair: Initiates synthesis of Vitamin D in response to UV radiation; contains immune cells (e.g., Langerhans cells) for pathogen detection; plays a central role in complex processes of tissue regeneration and wound healing.

    • Waste Excretion: Contributes to elimination of metabolic byproducts, including urea, lactic acid, and various salts, primarily through sweat.

  • Epidermis (thin, avascular, primarily composed of keratinocytes)

    • Stratum basale (germinativum): Deepest layer; single row of cuboidal or columnar cells; site of continuous cell division (mitosis) to replenish superficial layers; contains melanocytes (produce melanin for UV protection) and Merkel cells (involved in touch sensation).

    • Stratum spinosum (prickly layer): Several layers thick; cells interconnected by desmosomes (appear spiny); rich in keratinocytes undergoing maturation; contains Langerhans cells (immune function).

    • Stratum granulosum (granular layer): 3-5 layers of flattened keratinocytes containing lamellar granules (release lipids to form water barrier) and keratohyaline granules (involved in keratin aggregation).

    • Stratum lucidum (clear layer): Thin, clear layer found only in thick skin (palms and soles); cells are dead and flattened.

    • Stratum corneum (horny layer): Outermost, toughest layer; 20-30 layers of dead, flattened, keratin-filled cells (corneocytes); provides primary physical and chemical barrier function; continuously sheds (desquamates).

  • Dermis (thick, vascularized, connective tissue layer beneath epidermis)

    • Papillary layer: Superficial layer; composed of loose areolar connective tissue; forms dermal papillae (finger-like projections) that interdigitate with epidermal ridges, increasing surface area for nutrient exchange and strengthening dermal-epidermal junction; contains capillaries, lymphatic vessels, and Meissner's corpuscles (light touch receptors).

    • Reticular layer: Deeper, thicker layer; composed of dense irregular connective tissue with abundant bundles of collagen (for tensile strength) and elastic fibers (for elasticity); contains larger blood vessels, nerves, Pacinian corpuscles (deep pressure/vibration receptors), hair follicles, and glands.

  • Subcutaneous tissue (hypodermis) = primarily composed of loose connective tissue and adipose (fat) cells; functions include insulation against heat loss, cushioning against physical trauma, and serving as a major energy storage site; houses larger blood vessels and nerves that supply the skin.

  • Appendix structures (skin appendages)

    • Hair follicles: Invaginations of the epidermis extending into the dermis or subcutaneous tissue; produce hair shafts.

      • Vellus hair: Fine, short, non-pigmented; covers most of the body.

      • Terminal hair: Coarse, long, pigmented; found on scalp, eyebrows, eyelashes, and develops in axilla, pubic area, and face in males during puberty.

      • Pigment is derived from follicular melanocytes located in the hair bulb.

      • Hair growth phases: Anagen (growth), Catagen (regression), Telogen (resting).