Basics of dermatology😊

Basics of dermatology

Layers of Human Skin

• Epidermis

• Dermis

• Subcutaneous tissue

• Muscle

 

Key Layers:

Epidermis

• Mnemonic: "Come let's get sun burnt"
• C = Corneum
• L = Lucidum
• G = Granulosum
• S = Spinosum
• B = Basale

Histopathological Appearance

• Visible Epidermal Layers (Biopsy):
• Stratum corneum (topmost)
• Stratum granulosum
• Stratum spinosum
• Stratum basale
• NOT Lucidum

Formation Direction: 

• Bottom to top.
• Starts with Stratum basale.

Cell Differentiation

• Process:
• Cells form in basal layer.
• Move to stratum corneum.
• Changes during movement are cell differentiation.

• Changes:
• Become flatter.
• Increase in size.
• Lose nuclei.
• Become dehydrated and dry.

• Clinical Relevance:
• Pre-term baby: Absent stratum corneum (formed last).

Cell Kinetics / Epidermal Turnover Time

• Definition:
• Time for cells to form in basal layer.
• Move to stratum corneum.
• Exfoliate into environment.
• Continuous process.

• Normal Duration: 
• Approximately 52 to 75 days
• average 56 days (approx 2 months)

• Process Breakdown:



• 14 days to stratum corneum.
• 14 days for sloughing start.
• 28 days for complete slough.

• Disorders:
• Psoriasis:
• Turnover time reduces to 4 days (rapid multiplication).

Specific Epidermal Layers and Histopathological Findings

Stratum corneum

• Location: Topmost layer

• Composition:
• Dead layer of skin.
• Formed by dead keratinocytes.
• No nuclei, no organelles.
• Flat and dehydrated.

• Function: Barrier in the skin.

• Histopathological Changes:
• Normal: No nuclei.

Parakeratosis: 

• Retention of nuclei.
• Physiological: 
• Mouth, vagina (mucosal membranes).
• Pathological:
• Psoriasis
• Eczema
• Actinic keratosis
• Seborrheic dermatitis
• Note: Seborrheic keratosis does not show parakeratosis.
• SCC
• Mnemonic: PEAS2 (Psoriasis, Seborrheic dermatitis).

Hyperkeratosis: 

• Increased thickness.
• Normal Thickness: 4-6 layers.
• Mnemonic: Thick skin people → dont Like (Lichen Planus) Sorry (Psoriasis)
• Seen in:
• Psoriasis
• Lichen planus.

Stratum Lucidum (Special Layer)

• Presence:
• Only in palms and soles.
• Absent elsewhere.

• Function:
• Provides additional layer.
• Offers cushioning.

• Location: Thickest skin areas.

• Other Name: Clear cell layer.
• Histology: Cells appear clearer.
• D/t presence of refractile granules of eleidin.
• Mnemonic: L for lucidum, L for palms, soles, eLeidin.

• Mnemonic: Loosen → to kick and punch (palm and soles) Ellie (Eleidin)

Stratum Granulosum

• Appearance: Contains granules.

• Mnemonic: Granny

• Types of Granules:
• Keratohyaline granules (Profilaggrin):
• Profilaggrin converts to filaggrin.
• Filaggrin is barrier component in stratum corneum.
• Defective filaggrin: Ichthyosis vulgaris
• Mnemonic: Granny (Granulosum) Keriyapo (Keratohy) Fill (Filaggrin) ayi → Vulgur (Icthy Vulg)
• Odland bodies (Lipid-coated/membrane-coated granules):
• Contain fat.
• Important for skin adhesion, moisturization, barrier function.
• Defective Odland bodies: Asteatotic eczemas.
• Mnemonic: Granny () has Odd body (Odland) and Ass (Asteatotic eczema)
• Oil and - fat

• Thickness: Very thin layer (1-2 cell layers).

• Histopathological Features:



• Hypergranulosis: 
• Increased thickness.
• Seen in: Lichen planus.
• Mnemonic: We Like (Lichen) Hyper Grannies ()
• Agranulosis: 
• Absent granular layer.
• Seen in: Psoriasis.
• Mnemonic: If no granny (Agranu) → Sorry (Psoriasis) for ur loss
• Dyskeratosis: 
• Faulty keratinization/defect in keratinization.
• Increased cytoplasm, pyknotic nuclei
• Conditions:
• Benign: Hailey-Hailey, Darier's.
• Malignant: BCC, SCC, Paget's disease.
• Mnemonic:
• Girl with bad faulty skin says
• “Hai Hai () Darling (Darrier)”
• “If ur Busy (BCC), I will Page you (Pagets)”

Stratum Spinosum

• Appearance: Spines (projections).

• Projections: Desmosomes (adhesions between keratinocytes).β

• Other Name: Prickle cell layer.

• Thickness: Thickest layer of epidermis.

• Histopathological Changes:



• Acute eczema
• Spongiosis: Intercellular edema (white spaces between cells).
• Ballooning: Intracellular edema (cells ballooned out).
• Chronic eczemas
• Acanthosis: 
• Increased thickness
• Also seen in Psoriasis, Lichen planus
• Not to be confused with acantholysis.
• Mnemonic:
• Sponge and balloon are acutely eazzzy (acute eczema)
• Akkan → old woman → chronically eaazzy

Malpighian Layer

• Composition: Stratum basale + Stratum spinosum.

• Nature: Viable layer of the epidermis (living layer).

Stratum Basale

• Other Name: Germinative cell layer.

• Thickness: Single layer thick.

• Function: Responsible for formation of rest of epidermis.

• Histopathological Changes:
• Acantholysis: 
• Separation of keratinocytes.
• Seen in: Pemphigus group disorders.
• Mnemonic: Basil (SB) Pammi Pammi (Pemphgus) Akkane konnu (Acantholysis)
• Basal Cell Degeneration: 
• Degeneration of basal cells.
• Seen in: Lichenoid dermatitis (e.g., Lichen planus).
• Mnemonic: Basil () Like (Lichen) to degenerate () himself

Microabscesses in Dermatology

• Definition: Collections of inflammatory cells, usually in epidermis.

• Types and Locations:

Type	Cells	Location	Seen In
Munro's Microabscess Munro island is to see (cornea → corneum)	Neutrophils	Stratum corneum	Psoriasis
Kogoj's Spongiform Microabscess Kagoj → Bajaj → Had Spine	Neutrophils	Stratum spinosum	Pustular Psoriasis
Papillary Microabscesses Papilla → Dermal papilla → Dermatitis herpetiformis	IgA and Neutrophils	Dermal papilla	Dermatitis Herpetiformis
Eosinophilic Abscesses Eosinophil → in vessels → vessels are deep → Pemphigoid	Eosinophils	Stratum spinosum/basale	Bullous Pemphigoid
Pautrier's Microabscess Paultry → easily infected with fungus → fungoides	Neutrophils	ㅤ	Mycosis Fungoides

• Psoriasis
• Not sorry () to see Munro () island and Mr Bajaj (Kogoj)

Cells in the Epidermis

• Four Important Cells:
1. Keratinocytes
2. Langerhans cells
3. Melanocytes
4. Merkel cells

Location of Epidermal Cells

Dermoepidermal Junction (DEJ) / Basement Membrane Zone

• Definition: Junction between epidermis and dermis.

• Function: Adhesion and signalling.

• Composition: Collagen, predominantly Type IV.

• Complex Structure (from epidermis down):



Level	Component
Hemidesmosomes	BP antigens • BP 1 / 230 • BP 2 / 180
Lamina lucida	Laminin
Lamina densa	Collagen 4 (major collagen)
Sublamina densa	Collagen 7 (anchoring fibrils)

Mnemonic:

• Basement process
• 1st → Kurach idum → Hemi → Hemidesmosomes
• apo BP kuudi
• 1st → 230
• Then → 180
• 2nd → Loose aki idum → lamina lucida
• 3rd → Dense aaki idum → lamina densa → major collagen is densely put (type 4)
• 4th → density ichi kuraykkum → sublamina densa → sublamina seven (type 7)

Dermis

• Composition: Harbours blood vessels, nerves, lymphatics, fibers, etc.

• Main Fibers: 
• Type I and Type III collagen.
• Contrast with DEJ (Type IV collagen).

• Rete edges:
• Part if epidermis that invaginates into dermis

• Papillary Dermis: 
• Invaginates into epidermis, forming papillae.
• Meissner corpuscles are present here.

• Reticular Dermis: 
• Below papillary dermis, mainly fibers.

Clinical Image Interpretation:

• Arrow to Dermal papilla: Meissner corpuscles.
• Dermat Miss

• Arrow to Stratum basale: Merkel cells.
• Basil ne marakkalle

Skin Appendages

• Types: Hair, nail, and glands.

Panniculus Adiposus

• Definition: Layer of subcutaneous fat in mammalian skin.

• Functions:
• Insulation
• Protection
• Energy storage

• Absent in:
• Eyelid
• Nipple
• Scrotum (replaced by dartos muscle)
• Penis (replaced by Colles fascia)

Skin Lesions in Dermatology

• Categories: Primary, Secondary, Special.

Primary Skin Lesions

Secondary Skin Lesions

• Origin: Formed over primary skin lesions.

Scale

• Visible exfoliation of stratum corneum

Note

Typical Lesion	Seen in
Silvery white	• Psoriasis
Lacy white on mouth	• Lichen Planus
Greasy	• Seborrheic dermatitis
Fish-like	• Ichthyosis vulgaris
Collarette	• Pityriasis rosea • collarette of rose
Fine/Branny	• Pityriasis versicolor • Bra of different colors
Burrow	• Scabies
Comedones	• Acne
Target lesion	• Erythema multiforme

Lines in Dermatology

• Key Lines: Blaschko's lines, Langer's lines, Kraissl’s line

• Mnemonic: Cries (Kraissl’s line) due to tension

Blaschko's Lines

• Appearance: Curved, S-shapes.

• Nature: Lines of embryonic development.

• Constancy: Constant, do not change.

• Demarcation: Strict midline.

• Clinical Relevance: 
• Certain disorders (e.g., Incontinentia Pigmenti) follow these lines.

• Mnemonic: Blaschko's has "C in it" (constant, embryonic, midline).

Langer's Lines

 

• AKA relaxed tension lines.

• Appearance: Mostly straight, can be oblique, not curved.

• Nature: Lines of orientation of collagen muscle fibres.

• Constancy: Not constant, change with age.

• Clinical Relevance: 
• Surgery
• Important for surgical incisions
• Better healing
• Better scars
• Muscle action perpendicular to lines
• Forensic
• Stab wound parallel to Langer’s line:
• Decreased gaping.
• Stab wound perpendicular to Langer’s line:
• Increased gaping.

• Mnemonic: Langer's lines has "anger" (not constant, momentary).

Woods Lamb Examination

Mnemonic:

• NO (9% Nickel oxide) Bullshit (Barium silicate) in Woods

• 365 days (365nm) in wood

• Woman with green cap (tinea capitis green), yellow beaded pedant (yellow versicolor) around neck and red bikini (red → erythrasma) inside a forest full of wood (Woods lamp)

• Low output mercury arc lamp

• Covered with Wood’s filter (barium silicate + 9% nickel oxide)

• Emits UV light (320–450 nm, peak 365 nm)

• Clinical Uses:

Condition	Wood’s Lamp Finding
Vitiligo	Lesions accentuate
Tinea capitis	Greenish fluorescence
Pityriasis versicolor	Yellow fluorescence
Erythrasma	Coral red fluorescence
Congenital erythropoietic porphyria	Reddish fluorescence
Melasma	Differentiates epidermal vs dermal types

Skin Biopsy Types

1. Incision biopsy:
• Small part of lesion excised

2. Shave biopsy:
• Superficial;
• seborrheic or actinic keratosis

3. Punch biopsy:
• Most common
• Uses circular punch of various sizes
• Area is sutured after removal

4. Excision biopsy:
• For suspected malignancy
• Entire lesion is removed