Module 1: Dermatological Principles

1.1 Taking a Focused Dermatological History

A comprehensive dermatological history is the cornerstone of diagnosis. It should be systematic, patient-centred, and clinically oriented.

Key Components

1. Chief Complaint

   • Nature of the skin problem (e.g., rash, lesion, itch, discoloration).

2. History of Present Illness

   • Onset: Sudden or gradual?

   • Duration: Acute (<6 weeks) or chronic (>6 weeks)?

   • Progression: Static, spreading, or resolving?

   • Symptoms: Pruritus, pain, burning, bleeding, discharge.

   • Pattern: Intermittent or persistent?

   • Aggravating/Relieving Factors: Heat, cold, stress, sunlight, medications.

3. Past Dermatological History

   • Previous similar episodes, treatments used, and response.

4. Medical and Surgical History

   • Atopy, autoimmune diseases, diabetes, HIV, malignancies.

5. Drug History

   • Prescription, OTC, herbal, recent changes.

6. Family History

7. Psoriasis, eczema, vitiligo, skin cancers.
   Social and Occupational History

   • Exposure to chemicals, allergens, or infectious agents.

8. Travel History

   • Especially relevant for tropical or parasitic skin diseases.

1.2 Structured Skin Examination Techniques

A head-to-toe examination is essential. Use natural light or a dermatoscope as needed.

Steps

1. General Inspection

◦ Examine the entire skin surface, including the scalp, nails, mucosa, and intertriginous areas.

2. Lesion Assessment – “SALTSS” Mnemonic

◦ Site: Note the anatomical location and distribution.

◦ Arrangement: Identify if lesions are linear, grouped, annular, or dermatomal.

◦ Lesion Type: Determine if lesions are primary or secondary.

◦ Texture: Assess whether the surface is smooth, rough, or scaly.

◦ Size and Shape: Measure and describe.

◦ Surroundings: Look for erythema, oedema, or satellite lesions.

3. Palpation

◦ Feel for consistency, tenderness, temperature, mobility, and blanching.

4. Special Tests

◦ Diascopy: Apply a glass slide to assess blanching.

◦ Wood’s Lamp: Use for pigmentary disorders and infections.

◦ Dermatoscopy: Examine pigmented lesions and skin cancers.

1.3 Dermatological Terminology and Descriptions

Precise terminology improves communication and documentation.

Table 1.1: Primary Lesions:

Lesion	Description	Example
Macule	Flat, <1 cm	Freckle
Patch	Flat, >1 cm	Vitiligo
Papule	Raised, <1 cm	Wart
Plaque	Raised, >1 cm	Psoriasis
Vesicle	Fluid-filled, <1 cm	Herpes simplex
Bulla	Fluid-filled, >1 cm	Bullous pemphigoid
Pustule	Pus-filled	Acne
Nodule	Solid, deep	Dermatofibroma

Secondary Lesions

• Scale: Flakes of keratin (e.g., psoriasis)

• Crust: Dried serum or pus (e.g., impetigo)

• Erosion: Loss of epidermis

• Ulcer: Loss of epidermis and dermis

• Fissure: Linear crack

• Scar: Fibrous tissue replacing normal skin

• Lichenification: Thickened skin from chronic scratching

Distribution Patterns

• Symmetrical: Psoriasis
  [Update 2025 CDC/BASHH]: IL-17 and IL-23 inhibitors are preferred for biologic-naive patients with moderate-to-severe disease.

• Flexural: Atopic dermatitis

• Extensor: Psoriasis
  [Update 2025 CDC/BASHH]: IL-17 and IL-23 inhibitors are preferred for biologic-naive patients with moderate-to-severe disease.

• Dermatomal: Herpes zoster

• Photo-distributed: Lupus erythematosus

Anatomy of the Skin and Clinical Correlation

Understanding skin anatomy is crucial for localizing pathology and interpreting clinical signs (Fig. 1.1)

Fig. 1.1: Anatomy of the skin

1. Epidermis

• Layers: Stratum corneum → lucidum → granulosum → spinosum → basale

• Cells: Keratinocytes, melanocytes, Langerhans cells

• Clinical relevance:

  • Psoriasis: Hyperproliferation of keratinocytes

  • Vitiligo: Loss of melanocytes

  • Eczema: Barrier dysfunction

2. Dermis

• Components: Collagen, elastin, blood vessels, lymphatics, nerves

• Structures: Hair follicles, sebaceous and sweat glands

• Clinical relevance:

  • Urticaria: Vascular dilation

  • Lupus: Immune complex deposition

  • Cellulitis: Bacterial infection of dermis

3. Subcutaneous Tissue (Hypodermis)

• Function: Insulation, energy storage, shock absorption

• Clinical relevance:

  • Erythema nodosum: Inflammatory panniculitis

  • Lipomas: Benign fat tumours