Diseases of the Skin

Diseases of the Skin

Overview

  • Grouped by anatomical diagnosis

  • Anatomical diagnosis involves understanding the signs and symptoms of diseases

  • Focus is on identifying diseases, understanding associated tables, and engaging with case studies

  • Pictures will not be included on exams

  • Descriptions provided will correspond to presentation slides

  • Disease information includes:

    • Disease name

    • Organism responsible

    • Mode of transmission

    • Virulence factors

    • Methods of culture and diagnosis

    • Prevention strategies

    • Treatment options

    • Epidemiology notes

  • Important note that key information may be missing from slides.

Learning Objectives

  1. Skin anatomy and defenses

  2. Signs and symptoms associated with skin infections

  3. Bacterial infections

  4. Viral infections

  5. Fungal infections

  6. Parasitic infections

Learning Objective 1: Skin Anatomy

  • **Key points of entry: **

    • Epidermis

    • Dermis

    • Subcutaneous layer

    • Sweat pore

    • Capillaries

    • Sebaceous glands (oil glands)

    • Sweat gland ducts

    • Veins and arteries

    • Adipose connective tissue

    • Hair follicles

    • Openings of pores

    • Circulatory pathways

Skin Defenses

  • Physical blockages:

    • Keratin forms a protective barrier

    • Cell sloughing (desquamation) helps remove pathogens

  • Unfavorable environment for pathogens:

    • Low pH that inhibits growth

    • High salt concentrations

    • Oils (sebum) that deter microbial survival

  • Antimicrobial components:

    • Lysozymes that disrupt bacterial cell walls

    • Antimicrobial peptides that neutralize microorganisms

Normal Flora of the Skin

  • Common species include:

    • Staphylococcus epidermidis

    • Corynebacterium diphtheriae

    • Propionibacterium acnes

    • Candida sp. (a fungal species)

    • Staphylococcus aureus

  • Note: Viruses and parasites are also part of the skin microbiome, though they are less well characterized.

Learning Objective 2: Signs and Symptoms

  • Changes to skin due to infections are called lesions. Key types of lesions include:

    • Rashes

    • Pustules

    • Warts

    • Abscesses

  • Specific signs related to diseases:

    • Example: “Bullseye rash” is indicative of Lyme disease.

  • Describing lesions:

    • Changes include skin color or texture changes, fluid-filled lesions, etc.

      • Flat and discolored (e.g., vitiligo)

      • Raised and solid (e.g., warts)

    • Fluid-filled lesions:

      • Clear fluid filled lesions (vesicles)

      • Pus filled lesions (pustules).

  • Definition of pus:

    • Thick liquid resulting from dead white blood cells and dead microorganisms—indicative of infection.

    • Lesions containing pus are described as purulent.

Considerations for Treatment

  • Abscess:

    • Deep tissue pustule characterized by swelling and hardness

    • Blood flow is diminished, making antibiotics less effective

    • Often requires drainage to improve blood flow and facilitate treatment

Learning Objective 2 Vocabulary Review

  • “-itis” = inflammation or infection of a specific area (e.g., folliculitis is inflammation of hair follicles).

  • “-emia” = presence in the blood (e.g., septicemia means bacteria in the blood).

  • “cutaneous” = relating to the skin.

Simplified Overview of Diagnostic Lab Testing

  • Project goals in diagnostic testing:

    • Identify suspected cause.

    • Determine specimen collection and analyses needed.

  • Principle: “Garbage in, garbage out!”—quality of specimen impacts the outcome.

Diagnostic Laboratory Testing Approaches

  • For bacterial skin specimens:

    1. Culture using appropriate media (TSA, MacConkey agar, blood agar)

    2. Gram stain to determine cell characteristics

    3. Virulence factor testing

    4. Identifying organisms through flowchart methods (Distinguishing Gram-positive cocci from Gram-negative rods).

Bacterial Infections of the Skin (Learning Objective 3)

  1. Acne

    • Caused by Propionibacterium acnes, an anaerobic organism that is part of normal flora.

    • Transmission is opportunistic following skin blockage.

    • Treatment includes topical and systematic antibiotics.

    • Epidemiology: Common in adolescents and adults.

  2. Dermatitis

    • Caused by Pseudomonas aeruginosa, a strict aerobe and Gram-negative rod, commonly leads to