Principles of Diagnosis in Dermatology

Dermatological History - Clue Collector

• Presenting Complaint (PC):
  • Site, Symptoms (itch, pain), Severity
  • Onset, Duration, Course (progression, recurrence)
  • Aggravating/Relieving factors
  • Associated systemic symptoms (fever, malaise)
  • Previous episodes, treatments, response
• Past Medical History (PMH):
  • Atopy (eczema, asthma, rhinitis)
  • Other skin diseases, chronic illness (diabetes, immunosuppression)
• Drug History:
  • Current/recent medications (esp. new)
  • Allergies, prior adverse drug reactions

  ⭐ Drug history is key; some drugs cause severe reactions (SCARs) like Stevens-Johnson Syndrome (SJS).

• Family History: Similar conditions, hereditary disorders (ichthyosis, neurofibromatosis).
• Personal/Social History: Occupation, travel, sun exposure, pets, stress.

Skin Lesion Morphology - Skin Speak

Accurate lesion description is key. Primary lesions arise on normal skin; secondary lesions evolve or result from trauma (e.g., scratching).

• Primary Lesions: (Initial skin changes)
  • Macule: Flat, color change, <1cm. Patch: Larger macule, >1cm.
  • Papule: Solid, raised, palpable, <1cm. Plaque: Raised, flat-topped, >1cm (confluent papules).
  • Nodule: Solid, raised, deeper & firmer than papule, often >1cm.
  • Vesicle: Fluid-filled (serous), raised, <1cm. Bulla: Larger vesicle, >1cm.
  • Pustule: Vesicle/bulla containing pus.
  • Wheal: Transient, edematous, erythematous papule/plaque (e.g., urticaria).
• Secondary Lesions: (Evolved or trauma-induced)
  • Scale: Flakes of stratum corneum.
  • Crust: Dried exudate (serum, blood, pus).
  • Erosion: Superficial epidermal loss; heals without scar.
  • Ulcer: Deeper loss (dermis/subcutis); heals with scar.
  • Fissure: Linear crack in skin.
  • Lichenification: Thickened skin, exaggerated markings (chronic rubbing).
  • Atrophy: Thinning of skin layers.

⭐ Koebner Phenomenon (Isomorphic Response): Development of new lesions of a pre-existing dermatosis (e.g., psoriasis, lichen planus, vitiligo) at sites of skin trauma or injury.

Dermatological Examination - Dermo Detective Kit

• Inspection:
  • Good lighting; Magnifying lens/Dermatoscope.
  • Examine: skin, hair, nails, mucosa.
• Distribution:
  • Symmetry, sites (flexural, extensor, acral, dermatomal).
• Configuration:
  • Linear, annular, arcuate, grouped, serpiginous, reticular.
• Palpation:
  • Consistency, tenderness, temperature, depth.
• Key Signs & Tools:
  • Diascopy: Blanching (vascular).
  • Nikolsky's sign: Epidermal shear.
  • Auspitz sign: Bleeding on scale removal (psoriasis).
  • Darier's sign: Urtication on rubbing (mastocytosis).
  • Koebner phenomenon: Lesions at trauma sites.
  • Wood's Lamp: Fluorescence (e.g., Microsporum).

⭐ Auspitz sign: Characteristic pinpoint bleeding when scales are scraped off a psoriatic plaque; reveals underlying elongated, dilated dermal papillae.

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Diagnostic Procedures - Lab Lens

• KOH Mount: Fungal elements (dermatophytes, Candida). 10-20% KOH.
• Tzanck Smear: Multinucleated giant cells (Herpes), acantholytic cells (Pemphigus). Giemsa.
• Gram Stain: Bacteria.
• AFB Stain (ZN): Mycobacteria (leprosy, cutaneous TB).
• Wood's Lamp (UV-A 365nm):
  • Microsporum: Blue-green.
  • C. minutissimum: Coral-red (Erythrasma).
  • Malassezia: Yellow-orange (P. versicolor).
• Diascopy: Blanching (vascular) vs. non-blanching (hemorrhagic).
• Skin Biopsy: Punch, shave, excision for histopathology.

⭐ Wood's lamp: Corynebacterium minutissimum in erythrasma fluoresces coral-red.

High‑Yield Points - ⚡ Biggest Takeaways

• Thorough history and lesion morphology (type, shape, distribution) are paramount.
• Diascopy differentiates blanchable erythema from non-blanchable purpura.
• Wood's lamp detects specific fungal infections (e.g., Microsporum green fluorescence) and erythrasma (coral red).
• KOH mount is vital for confirming superficial fungal infections by visualizing hyphae.
• Tzanck smear identifies multinucleated giant cells in herpetic infections.
• Skin biopsy is often the gold standard for definitive diagnosis, especially for tumors.
• Dermoscopy improves melanoma detection by visualizing subsurface structures.