Dermatological Procedures

Diagnostic Procedures - Sleuthing Skin Secrets

• Skin Biopsy: Gold standard for many dermatoses.
  • Punch: Common, provides full-thickness sample.
  • Shave: For superficial lesions (e.g., skin tags, seborrheic keratosis).
  • Excisional: Removes entire lesion; diagnostic & therapeutic.
  • Incisional: Removes portion of a large lesion.
• KOH Mount: 10-20% Potassium hydroxide; dissolves keratin to visualize fungal hyphae/spores (e.g., dermatophytes, Candida).
• Tzanck Smear: Giemsa/Wright stain; detects multinucleated giant cells in viral infections (Herpes simplex, Varicella-zoster).
• Wood's Lamp (UV-A, 320-400 nm, peak 365 nm): Filtered UV light.
  • Microsporum spp.: Blue-green fluorescence.
  • Corynebacterium minutissimum (Erythrasma): Coral-red.
  • Pityriasis versicolor: Yellowish-gold.
  • Vitiligo: Accentuated depigmentation (chalky white).
• Diascopy: Pressing a glass slide on a lesion.
  • Differentiates erythema (blanchable, vascular) from purpura/petechiae (non-blanchable, hemorrhagic).
• Patch Test: Identifies allergens in allergic contact dermatitis (Type IV hypersensitivity). Readings at 48 & 72-96 hours.
• Dermoscopy (Epiluminescence Microscopy): Non-invasive, magnified view of skin surface structures; aids early melanoma detection.

⭐ Diascopy is crucial in distinguishing a vascular lesion (e.g., spider angioma, which blanches) from a hemorrhagic lesion (e.g., petechia, which does not blanch).

Minor Surgical & Destructive Procedures - Scalpel & Spark

Scalpel Procedures:

• Skin Biopsy: Diagnostic sampling.
  • Punch Biopsy: 3-4 mm common. Stretch ⊥ RSTLs → oval wound, better cosmesis. To subcutaneous fat. Suture if >4 mm.
  • Shave Biopsy: Superficial lesions (e.g., skin tags, seborrheic keratosis). Blade parallel. Minimal scarring.
  • Excisional Biopsy: Full lesion + margin (L:W 3:1). For suspected melanoma, small BCC/SCC.
  • Incisional Biopsy: Wedge from large lesion/critical site.
• Curettage: Scraping with curette (molluscum, SK, AK, superficial BCC). Often + electrodesiccation (hemostasis).

Destructive Procedures ("Spark"):

• Electrosurgery: High-frequency current for destruction/cutting.
  • Fulguration: Sparking, superficial (tags, angiomas).
  • Desiccation: Contact, dehydrates (warts, acrochordons).
  • Coagulation: Deeper, hemostasis (bleeder control).
  • Electrosection: Cutting current (pedunculated nevi).
  • ⚠️ Pacemakers, ICDs.
• Cryosurgery: LN2 ($-196^ ext{o} ext{C}$). Rapid freeze, slow thaw → cell necrosis.
  • Uses: Warts, AK, molluscum. 1-3 cycles, 10-30s freeze.
• Chemical Cautery: Topical corrosives.
  • Agents: TCA (30-100%), podophyllin, salicylic acid.
  • Uses: Warts (TCA/salicylic), xanthelasma (TCA).

⭐ Punch biopsy: Stretch skin ⊥ RSTLs → oval wound, better cosmesis & closure.

Phototherapy & Lasers - Light & Might

• Phototherapy (UV Light)

  • UVB Therapy:
    • Broad-Band (BB-UVB): 290-320 nm. Psoriasis, vitiligo.
    • Narrow-Band (NB-UVB): 311-313 nm. More effective, safer for psoriasis, vitiligo, atopic dermatitis. Mechanism: Immunomodulation.
  • PUVA (Psoralen + UVA):
    • Oral/topical psoralen + UVA (320-400 nm).
    • Indications: Severe psoriasis, vitiligo, mycosis fungoides.
    • Side effects: Phototoxicity, nausea, ↑Skin Cancer (SCC) risk.
    • 📌 Mnemonic: Psoralen Used Vith A-light.
  • Combination Regimens: Goeckerman (coal tar + UVB), Ingram (anthralin + UVB) for psoriasis.

• Lasers (Light Amplification by Stimulated Emission of Radiation)

  • Principle: Selective photothermolysis (targets specific chromophores).
  • Common Lasers & Targets (Chromophore):
    • Pulsed Dye Laser (PDL): 585/595 nm (Oxyhemoglobin) → Vascular lesions (Port-wine stain, rosacea).
    • Nd:YAG: 1064 nm (Melanin, Tattoo ink) → Hair removal (dark skin), Tattoos.
      • KTP (freq-doubled Nd:YAG): 532 nm (Melanin, Oxyhemoglobin) → Lentigines, superficial vessels.
    • Alexandrite: 755 nm (Melanin) → Hair removal (fair skin), pigmented lesions.
    • CO2: 10600 nm (Water) → Ablative resurfacing, warts, rhinophyma.
    • Erbium:YAG (Er:YAG): 2940 nm (Water) → Ablative resurfacing (less thermal damage).
    • Excimer: 308 nm (DNA) → Localized psoriasis, vitiligo.

⭐ NB-UVB (311-313 nm) is preferred over BB-UVB for psoriasis due to better efficacy and safety profile, requiring lower cumulative doses and having a lower carcinogenic risk compared to PUVA.

High‑Yield Points - ⚡ Biggest Takeaways

• Wood's lamp (UVA light): Key for tinea capitis (green fluorescence), erythrasma (coral-red), pityriasis versicolor (yellowish).
• Diascopy: Differentiates vascular lesions (blanchable) from hemorrhagic lesions (non-blanchable).
• Tzanck smear: Detects multinucleated giant cells in herpetic infections (HSV, VZV).
• KOH mount: Essential for diagnosing fungal infections by visualizing hyphae and spores.
• Patch testing: Gold standard for allergic contact dermatitis (Type IV hypersensitivity).
• Punch biopsy: Obtains full-thickness skin sample for definitive histopathological diagnosis.
• Cryotherapy (liquid nitrogen): Common for warts, molluscum, actinic keratoses treatment by inducing frostbite.