Module 1.1 - Papules, Pustules, Erythema
ANATOMY OF THE SKIN
(Fitzpatricks Dermatology Secrets Plus, 4E)
Recall the Structure and Function of the Skin THE THREE LAYERS OF THE SKIN
1. Epidermis
ANATOMY OF THE SKIN ● Composition: Outermost layer, made up of keratinocytes (epidermal cells).
(Fitzpatricks Dermatology Secrets Plus, 4E) ● Four Layers:
○ Basal Cell Layer (Stratum Basalis):
■ Composed of columnar or cuboidal cells.
■ Direct contact with basement membrane.
■ Contains germinative cells (mitoses may occur).
○ Spiny Cell Layer (Stratum Spinosum):
■ High concentration of desmosomes and keratin filaments.
■ Characteristic "spiny" appearance.
○ Granular Cell Layer (Stratum Granulosum):
■ Formation of keratohyalin granules.
■ Granules bind to keratin filaments, creating large electron-dense masses.
■ "Granular" appearance.
○ Cornified Layer (Stratum Corneum):
■ Keratinocytes lose organelles and nuclei.
■ Keratin filaments and keratohyalin granules form an amorphous mass.
■ Keratinocytes become elongated and flattened, forming "corneocytes."
■ Corneocytes held together by desmosome remnants and a "cementing substance" from
Odland bodies.
● Other Cell Types:
○ Melanocytes:
■ Dendritic cells in the basal cell layer.
■ Synthesizes and secretes melanin-containing organelles (melanosomes).
■ Approximately 36 keratinocytes per melanocyte.
○ Langerhans Cells:
■ Bone marrow-derived, antigen-presenting cells.
■ Found primarily in the stratum spinosum.
■ Important for immune surveillance.
○ Merkel Cells:
■ Contact with nerve fibrils.
■ Contain electron-dense bodies similar to APUD cells.
● Apocopation:
○ Process where melanocytes transfer melanosomes to keratinocytes.
○ Keratinocytes phagocytize the tips of melanocytic dendritic processes.
● Basement Membrane Zone (BMZ):
, ○ Not visible with hematoxylin-eosin staining; visible with periodic acid-Schiff staining.
○ Complex structure attaching basal cell layer to dermis.
○ Includes hemidesmosomes, anchoring filaments, and anchoring fibrils.
● Functions:
○ Protection: Barrier against toxins and desiccation.
○ Prevention of Desiccation: Maintains skin hydration.
○ Immune Surveillance: Langerhans cells process and present antigens.
2. Dermis
● Composition:
○ Beneath the epidermis.
○ Composed of collagen, elastin, and proteoglycans.
○ Contains hair follicles, sebaceous glands, apocrine glands, eccrine glands, blood vessels,
lymphatics, and nerves.
● Main Cell Type:
○ Fibroblasts:
■ Produce collagen (70-80%), elastin (1-3%), and proteoglycans (mainly hyaluronic acid).
● Components:
○ Collagen: Types I and III, organized into bundles running horizontally.
○ Elastic Fibers: Interspersed among collagen fibers.
○ Oxytalan Fibers: Small elastic fibers in the papillary dermis, oriented perpendicularly.
○ Proteoglycans: Hyaluronic acid in the ground substance around fibers.
● Functions:
○ Temperature Regulation: Through blood flow and sweating.
○ Mechanical Protection: Provided by collagen and hyaluronic acid.
○ Innervation: Responsible for cutaneous sensation.
● Skin Innervation:
○ Large Myelinated Nerves: Branch in the subcutaneous tissue to form deep nerve plexus, then
ascend to form superficial subpapillary plexus.
○ Free Nerve Endings: Sensory receptors for touch, pain, temperature, itch, and mechanical
stimuli.
○ Corpuscular Receptors:
■ Meissner Corpuscles: Found in glabrous skin, respond to touch.
■ Pacinian Corpuscles: Found in deep dermis and subcutaneous tissue, respond to
vibration.
■ Ruffini Corpuscles: Rare, involved with collagen in digits.
■ Golgi-Mazzoni Corpuscles: Found on fingers, laminated structure.
■ Krause End Bulbs: Encapsulated endings in papillary dermis.
3. Subcutis/Hypodermis
● Location: Below the dermis.
● Composition:
○ Adipose tissue.
○ Larger blood vessels and nerves.
, ○ May contain bases of hair follicles and sweat glands.
○ Arranged into fat lobules divided by fibrous septae (collagen).
● Functions:
○ Caloric Reserve: Stores energy.
○ Heat Insulator: Regulates body temperature.
○ Shock Absorber: Protects underlying structures.
DIAGNOSTIC APPROACH TO A Dermatologic Diagnosis and Examination
DERMATOLOGIC PATIENT ● Diagnosis and Treatment of Cutaneous Diseases
Fitzpatrick’s Dermatology in General Medicine ○ Key Skills Required:
[9E] ■ Recognize primary lesions and reaction patterns of the skin.
■ Contextualize visual clues with the patient’s history and overall health.
■ Identifying morphology (shape, color, distribution) is crucial for differential diagnosis and
clinical documentation.
● Approach to the Patient
○ History:
■ Essential for establishing a diagnosis and assessing therapy suitability.
■ Important for complex cases (e.g., rash with fever, generalized pruritus).
■ Detailed history helps with diagnosis, monitoring, and treatment adjustments.
■ Table 1-1 provides a guide for history-taking based on the complaint type (growth,
eruption, nail or hair disorder).
○ Physical Examination:
■ Scope:
■ Inspect entire skin surface, including scalp, eyelids, ears, genitals, buttocks,
perineum, and interdigital spaces.
■ Examine hair, nails, and mucous membranes.
■ Comprehensive examination can identify harmful lesions, additional diagnostic
clues, and educate patients.
■ Table 1-2 guides the physical examination process.
■ Ideal Conditions:
■ Good lighting (preferably natural light) is crucial.
■ Patient should be fully undressed and gowned.
■ Comfortable examining table and room temperature.
■ Room should have handwashing facilities and disinfecting foam.
■ Chaperone may be needed if patient and physician are of opposite genders.
■ Recommended Tools:
■ Magnifying Tools: Loupe, magnifying glass, dermatoscope.
■ Lighting: Flashlight or penlight.
■ Miscellaneous:
■ Glass slides for various tests (diasiopy, DFA, fungal, Tzanck smears).
■ Alcohol pads, gauze, tissues for cleaning.
■ Gloves for contagious conditions or sensitive areas.
, ■ Ruler for measuring lesions.
■ Scalpel blades (No. 15 for scraping, No. 11 for incising).
■ Diagnostic solutions (potassium hydroxide, oil, culture media).
■ Camera for documentation.
■ Wood lamp for pigmentary changes.
■ Examination Technique:
■ Procedure:
■ Observe patient from a distance for general impressions.
■ Conduct systematic examination from head to toe, uncovering one area at
a time.
■ Adjust illumination and patient positioning as needed.
■ Use side lighting to reveal depth and lesion borders.
■ Palpate lesions to assess texture and tenderness.
■ Dermatoscope for pigmented lesions.
■ Examine mucosal sites with additional illumination.
■ Post-Examination:
■ Document findings descriptively or on a body map.
■ Use photography and anatomical landmarks for lesions requiring biopsy to
ensure accurate follow-up.
DIFFERENT TYPES OF SKIN LESIONS Primary Lesions
(Harrison's Principles of Internal Medicine, 20E) ● Macule:
○ Flat, colored lesion <2 cm, not raised.
○ Not palpable, well or ill-defined, any size or color.
○ Examples:
■ White: Vitiligo
■ Brown: Café-au-lait spots
■ Blue: Mongolian spots
■ Red: Port-wine stains, erythema
ANATOMY OF THE SKIN
(Fitzpatricks Dermatology Secrets Plus, 4E)
Recall the Structure and Function of the Skin THE THREE LAYERS OF THE SKIN
1. Epidermis
ANATOMY OF THE SKIN ● Composition: Outermost layer, made up of keratinocytes (epidermal cells).
(Fitzpatricks Dermatology Secrets Plus, 4E) ● Four Layers:
○ Basal Cell Layer (Stratum Basalis):
■ Composed of columnar or cuboidal cells.
■ Direct contact with basement membrane.
■ Contains germinative cells (mitoses may occur).
○ Spiny Cell Layer (Stratum Spinosum):
■ High concentration of desmosomes and keratin filaments.
■ Characteristic "spiny" appearance.
○ Granular Cell Layer (Stratum Granulosum):
■ Formation of keratohyalin granules.
■ Granules bind to keratin filaments, creating large electron-dense masses.
■ "Granular" appearance.
○ Cornified Layer (Stratum Corneum):
■ Keratinocytes lose organelles and nuclei.
■ Keratin filaments and keratohyalin granules form an amorphous mass.
■ Keratinocytes become elongated and flattened, forming "corneocytes."
■ Corneocytes held together by desmosome remnants and a "cementing substance" from
Odland bodies.
● Other Cell Types:
○ Melanocytes:
■ Dendritic cells in the basal cell layer.
■ Synthesizes and secretes melanin-containing organelles (melanosomes).
■ Approximately 36 keratinocytes per melanocyte.
○ Langerhans Cells:
■ Bone marrow-derived, antigen-presenting cells.
■ Found primarily in the stratum spinosum.
■ Important for immune surveillance.
○ Merkel Cells:
■ Contact with nerve fibrils.
■ Contain electron-dense bodies similar to APUD cells.
● Apocopation:
○ Process where melanocytes transfer melanosomes to keratinocytes.
○ Keratinocytes phagocytize the tips of melanocytic dendritic processes.
● Basement Membrane Zone (BMZ):
, ○ Not visible with hematoxylin-eosin staining; visible with periodic acid-Schiff staining.
○ Complex structure attaching basal cell layer to dermis.
○ Includes hemidesmosomes, anchoring filaments, and anchoring fibrils.
● Functions:
○ Protection: Barrier against toxins and desiccation.
○ Prevention of Desiccation: Maintains skin hydration.
○ Immune Surveillance: Langerhans cells process and present antigens.
2. Dermis
● Composition:
○ Beneath the epidermis.
○ Composed of collagen, elastin, and proteoglycans.
○ Contains hair follicles, sebaceous glands, apocrine glands, eccrine glands, blood vessels,
lymphatics, and nerves.
● Main Cell Type:
○ Fibroblasts:
■ Produce collagen (70-80%), elastin (1-3%), and proteoglycans (mainly hyaluronic acid).
● Components:
○ Collagen: Types I and III, organized into bundles running horizontally.
○ Elastic Fibers: Interspersed among collagen fibers.
○ Oxytalan Fibers: Small elastic fibers in the papillary dermis, oriented perpendicularly.
○ Proteoglycans: Hyaluronic acid in the ground substance around fibers.
● Functions:
○ Temperature Regulation: Through blood flow and sweating.
○ Mechanical Protection: Provided by collagen and hyaluronic acid.
○ Innervation: Responsible for cutaneous sensation.
● Skin Innervation:
○ Large Myelinated Nerves: Branch in the subcutaneous tissue to form deep nerve plexus, then
ascend to form superficial subpapillary plexus.
○ Free Nerve Endings: Sensory receptors for touch, pain, temperature, itch, and mechanical
stimuli.
○ Corpuscular Receptors:
■ Meissner Corpuscles: Found in glabrous skin, respond to touch.
■ Pacinian Corpuscles: Found in deep dermis and subcutaneous tissue, respond to
vibration.
■ Ruffini Corpuscles: Rare, involved with collagen in digits.
■ Golgi-Mazzoni Corpuscles: Found on fingers, laminated structure.
■ Krause End Bulbs: Encapsulated endings in papillary dermis.
3. Subcutis/Hypodermis
● Location: Below the dermis.
● Composition:
○ Adipose tissue.
○ Larger blood vessels and nerves.
, ○ May contain bases of hair follicles and sweat glands.
○ Arranged into fat lobules divided by fibrous septae (collagen).
● Functions:
○ Caloric Reserve: Stores energy.
○ Heat Insulator: Regulates body temperature.
○ Shock Absorber: Protects underlying structures.
DIAGNOSTIC APPROACH TO A Dermatologic Diagnosis and Examination
DERMATOLOGIC PATIENT ● Diagnosis and Treatment of Cutaneous Diseases
Fitzpatrick’s Dermatology in General Medicine ○ Key Skills Required:
[9E] ■ Recognize primary lesions and reaction patterns of the skin.
■ Contextualize visual clues with the patient’s history and overall health.
■ Identifying morphology (shape, color, distribution) is crucial for differential diagnosis and
clinical documentation.
● Approach to the Patient
○ History:
■ Essential for establishing a diagnosis and assessing therapy suitability.
■ Important for complex cases (e.g., rash with fever, generalized pruritus).
■ Detailed history helps with diagnosis, monitoring, and treatment adjustments.
■ Table 1-1 provides a guide for history-taking based on the complaint type (growth,
eruption, nail or hair disorder).
○ Physical Examination:
■ Scope:
■ Inspect entire skin surface, including scalp, eyelids, ears, genitals, buttocks,
perineum, and interdigital spaces.
■ Examine hair, nails, and mucous membranes.
■ Comprehensive examination can identify harmful lesions, additional diagnostic
clues, and educate patients.
■ Table 1-2 guides the physical examination process.
■ Ideal Conditions:
■ Good lighting (preferably natural light) is crucial.
■ Patient should be fully undressed and gowned.
■ Comfortable examining table and room temperature.
■ Room should have handwashing facilities and disinfecting foam.
■ Chaperone may be needed if patient and physician are of opposite genders.
■ Recommended Tools:
■ Magnifying Tools: Loupe, magnifying glass, dermatoscope.
■ Lighting: Flashlight or penlight.
■ Miscellaneous:
■ Glass slides for various tests (diasiopy, DFA, fungal, Tzanck smears).
■ Alcohol pads, gauze, tissues for cleaning.
■ Gloves for contagious conditions or sensitive areas.
, ■ Ruler for measuring lesions.
■ Scalpel blades (No. 15 for scraping, No. 11 for incising).
■ Diagnostic solutions (potassium hydroxide, oil, culture media).
■ Camera for documentation.
■ Wood lamp for pigmentary changes.
■ Examination Technique:
■ Procedure:
■ Observe patient from a distance for general impressions.
■ Conduct systematic examination from head to toe, uncovering one area at
a time.
■ Adjust illumination and patient positioning as needed.
■ Use side lighting to reveal depth and lesion borders.
■ Palpate lesions to assess texture and tenderness.
■ Dermatoscope for pigmented lesions.
■ Examine mucosal sites with additional illumination.
■ Post-Examination:
■ Document findings descriptively or on a body map.
■ Use photography and anatomical landmarks for lesions requiring biopsy to
ensure accurate follow-up.
DIFFERENT TYPES OF SKIN LESIONS Primary Lesions
(Harrison's Principles of Internal Medicine, 20E) ● Macule:
○ Flat, colored lesion <2 cm, not raised.
○ Not palpable, well or ill-defined, any size or color.
○ Examples:
■ White: Vitiligo
■ Brown: Café-au-lait spots
■ Blue: Mongolian spots
■ Red: Port-wine stains, erythema
