Other Signs: Bedside Diagnostic Tests

Introduction

Dermatology has a unique toolkit of physical maneuvers that can be performed at the bedside to elicit specific signs. These tests often provide the "clinch" for a diagnosis.

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8.1 Testing Vascular Integrity

Diascopy (Vitropressure)

Technique: Press a glass slide (or clear ruler) firmly against a red lesion.

• Purpose: Differentiates Erythema from Purpura.
  • Blanching: The redness disappears. Indicates dilated vessels (Erythema).
    • Examples: Urticaria, Viral Exanthem, Drug Rash.
  • Non-Blanching: The redness persists. Indicates blood outside the vessels (Purpura).
    • Examples: Vasculitis, Meningococcemia.
  • Apple Jelly Sign: Yellow-brown color revealed after blanching. Indicates granulomatous infiltrate.
    • Examples: Sarcoidosis, Lupus Vulgaris.

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8.2 Testing Epithelial Adhesion

Nikolsky Sign

Technique: Apply tangential (lateral) pressure with a finger on normal-appearing skin adjacent to a blister.

• Positive: The epidermis slides off like wet tissue paper.
• Significance: Indicates intra-epidermal loss of adhesion (acantholysis or necrosis).
  • Conditions: Pemphigus Vulgaris, SJS/TEN, Staphylococcal Scalded Skin Syndrome.
• False Nikolsky (Shewhart's Sign): Only the blister roof moves (subepidermal bulla). Seen in Pemphigoid.

Asboe-Hansen Sign (Bulla Spread Sign)

Technique: Apply vertical pressure directly on the center of an intact bulla.

• Positive: The blister expands laterally into surrounding skin.
• Significance: Similar to Nikolsky; confirms weak structural integrity of the blister roof.

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8.3 Testing Mechanical Reactivity

Dermographism ("Skin Writing")

Technique: Stroke the skin firmly with a blunt object (tongue depressor, capped pen).

• Positive: A linear wheal (hive) develops within 2-5 minutes.
• Significance: Physical Urticaria (Mast cell instability).

Darier’s Sign

Technique: Rub a brown macule firmly.

• Positive: The lesion swells, becomes itchy, and develops a surrounding flare (wheal).
• Significance: Mastocytosis (Urticaria Pigmentosa). Mechanical degranulation of mast cells in the lesion.

Auspitz Sign

Technique: Gently scrape the scale off a plaque with a glass slide or curette.

• Positive: Pinpoint bleeding spots appear.
• Significance: Psoriasis. Represents rupture of dilated capillaries in the thinned suprapapillary plates.

Koebner Phenomenon (Isomorphic Response)

Observation: Appearance of new lesions at sites of trauma (scratch, surgical scar) in uninvolved skin.

• Significance:
  • True Koebner: Psoriasis, Lichen Planus, Vitiligo.
  • Pseudo-Koebner: Bacterial seeding (Warts, Molluscum).

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8.4 Testing Sensation and Nerves

Histamine Test (Lewis Triple Response)

Technique: Scratch or prick skin.

1. Red reaction (Capillary dilation).
2. Wheal (Edema).
3. Flare (Axon reflex vasodilation).

• Significance: In leprosy (anesthetic patches), the Flare is absent because the axon reflex is destroyed.

Tangle Test (Hair)

Technique: Gently rub hair in different directions.

• Significance: In Woolly Hair or uncombable hair syndrome, the hair mats together violently.

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8.5 "Squeeze" Diagnostic Tests

Dimple Sign (Fitzpatrick’s Sign)

Technique: Pinch the skin on either side of a pigmented nodule.

• Positive: The lesion retracts downwards (dimples).
• Negative: The lesion protrudes upwards.
• Significance: Distinguishes Dermatofibroma (Positive) from Nevus/Melanoma (Negative).

Buttonhole Sign

Technique: Compress a soft nodule; it invaginates into the subcutis like a hernia.

• Significance: Neurofibroma (NF1).

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8.6 Diagnosis by Light

Wood's Lamp (365nm UV-A)

Technique: Examine skin in a pitch-black room.

• Fluorescence Colors:
  • Coral Red: Corynebacterium (Erythrasma).
  • Yellow-Green: Microsporum (Tinea Capitis).
  • Pale Blue/White: Depigmentation (Vitiligo - sharp contrast vs Hypopigmentation).
  • Pink/Orange: Porphyrins (Porphyria Cutanea Tarda urine/skin).

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Summary of Bedside Manuevers