This document summarizes several common bedside dermatology tests, including potassium hydroxide mount, Tzanck smear, slit skin smear, dark field microscopy, diascopy, intradermal tests, skin biopsy, Wood's lamp, dermatoscopy, and Nikolsky sign. It provides details on the procedures, indications, and findings of each test to aid in the diagnosis of various skin conditions.

1. Bedside Tests
in
Dermatology
Dr. Nishkarsh Chugh
PG Resident, Dept. of Dermatology

2. Potassium Hydroxide Mount
Presentation title
A potassium hydroxide (KOH) mount of
a skin scraping is a commonly
performed procedure to demonstrate the
evidence of fungal infection in the skin,
hairs, and nails.
2

3. KOH Mount
Procedure
1. Sample collection
2. Potassium hydroxide mount
3. Microscopic examination
Diagnostic Uses
• Dermatophytic infection of skin, hair,
and nails
• Candidiasis
• Pityriasis versicolor
• Other fungal infections like tinea nigra
and deep fungal infections.
• Scabies and other mites
• Bacterial vaginosis
3

4. Tzanck Smear
Presentation title
Tzanck smear is a very simple and rapid
office technique for cytodiagnosis of
infective and immunobullous conditions
and cutaneous tumors.
4

5. Tzanck Smear
Procedure
5
The area is cleaned and allowed to dry
A sterile needle is inserted at the base of the blister
Smear is taken from the base of the blister that contains
acantholytic cells
The smear is then prepared on a clean glass slide and
stained with Leishman Stain
The smear shows the presence of Tzanck cell which
are formed following detatchment, disintegration and
dissolution of normal squamous cell

6. Tzanck Smear
6
Diagnostic Uses
Disease Finding
Pemphigus Acantholytic cells (rounded cells with a relatively large nucleus and a condensed
cytoplasm) with hazy nucleoli
Bullous pemphigoid Non-specific findings. Scarcity of epithelial cells and an abundance of leukocytes,
particularly eosinophils with leukocyte adherence, is seen
Stevens-Johnson syndrome No acantholytic cells, but plenty of leukocytes
Toxic epidermal necrolysis Necrotic basal cells and leukocytes
Staphylococcal scalded skin syndrome Minimal or no inflammation, dyskeratotic Acantholytic cells
Herpes simplex, varicella, herpes zoster Ballooning multinucleate giant cells
Molluscum contagiosum Henderson-Patterson bodies
Leishmaniasis Leishman-Donovan bodies
Hailey-Hailey disease Acantholytic cells with normal nucleoli
Darier’s disease Corps, ronds and grains
BCC Basaloid cells
Paget’s disease of breast Paget cells
Mastocytoma Mast cells
Histiocytosis Atypical Langerhan cells

7. Slit Skin Smear
Presentation title
It is the most important lab test to detect
lepra bacilli in suspected Hansen’s
patches
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8. Slit Skin Smear
Role
• To confirm the diagnosis of leprosy
• To classify the disease
• To determine the disease activity in a
patient
• To assess progress of the disease
• To follow-up patients on treatment
Sites
1. Right earlobe
2. Forehead
3. Chin
4. Left buttock in men and left upper
thigh in women
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9. Slit Skin Smear
Procedure
9
Lesion is cleaned with spirit.
After pinching the skin between thumb and index
finger, a 5mm long and 2mm deep cut is made
with sterile blade (Bard Parker No. 15)
Base is scraped and the material is smeared (8-
10mm) on a glass slide.
After drying and heat fixing the smear, Ziehl-
Neelsen staining is done.

10. Slit Skin Smear
Bacterial Index Morphological Index
Percentage of solid stained bacilli,
calculated after examining 200 bacilli
lying singly
Bacilli are considered solid staining if:
1. Entire organism is uniformly stained
2. Longitudinal sides are parallel
3. Both ends are rounded
4. Length is five times its width
10
0 0 bacilli in 100 OIFs
1+ 1-10 bacilli/100 fields
2+ 1-10 bacilli/10 fields
3+ 1-10 bacilli/field
4+ 10-100 bacilli/field
5+ 100-1000 bacilli/field
6+ >1000 bacilli/field

11. Dark Field Microscopy
Presentation title
It is the most specific and sensitive
technique to diagnose syphilis when an
active chancre or condyloma lata is
present
11

12. Dark Field Microscopy
Principle
The dark ground microscope creates a
contrast between the object and the
surrounding field, such that, the
background is dark and the object is
bright.
Interpretation
Treponema pallidum appear as brightly
illuminated objects against a dark background.
0.25-0.3µm wide and 6-16µm long
organism with 8-14 regular, tightly wound, deep
spirals.
It exhibits quick and abrupt movements.
The organism rotates slowly along the
longitudinal axis (corkscrew motion)
accompanied by bending and twisting in the
middle. 12

13. Diascopy
Presentation title
Pressing a glass slide or a clear,
colourless piece of plastic onto the skin
compresses blood out of small vessels,
to allow evaluation of other colours.
13

14. Diascopy
Typical Uses
1. Granulomatous lesions: Yellowish green color is seen in plaques of lupus vulgaris
known as apple jelly nodules and grains of sand appearance in sarcoidosis.
2. To distinguish between nevus depigmentosus and nevus anemicus – in nevus
anemicus, there is a localised area of vasoconstriction, other pigments are unaltered
– diascopy of adjacent skin therefore reveals an identical colour to that of the
‘depigmented’ area.
3. Application of medium pressure to a spider naevus can compress radiating
arterioles and allow visualisation of pulsatile flow in the feeding vessel.
14

15. Intradermal Tests
Presentation title
Intradermal tests are widely used in
dermatology to support the diagnosis of
infectious diseases as well as for
detection of immediate (Type I) and
delayed (Type IV) hypersensitivity
towards exogenous or endogenous
antigens.
15

16. Intradermal Tests
Technique
The antigen is injected into the superficial
layer of the dermis through a fine-bore
(26 or 27-G) needle with its bevel
pointing upward.
The usual quantity injected is 0.1 mL.
The proximal part of the flexor aspect of
the forearm is conventionally used.
Interpretation
Tests for the detection of DTH are
typically read at 48–72 hours. The size of
the induration is more important than
erythema while interpreting Type IV
hypersensitivity.
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17. Skin Biopsy
Presentation title
A skin biopsy is a simple procedure of
great diagnostic importance and serves
as a permanent record of the skin
pathology. The biopsy may be subjected
to histopathological examination or to
other specialized techniques
(immunofluorescence, electron
microscopy, etc.)
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18. Skin Biopsy
Types
1. Incisional
2. Superficial shave biopsy
3. Punch biopsy
4. Excisional
Choice of Lesion
• Fully evolved, untreated lesion
• In blistering disorders, the smallest vesicle should
be biopsied to keep the roof intact.
• Excoriated or ulcerated lesions or lesions modified
because of steroid application should be avoided.
• Advancing edge with maximal elevation should be
biopsied for annular lesions such as granuloma
annulare or porokeratosis.
• Sites to be avoided: legs, bony prominences, and
pressure bearing areas
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19. Wood’s Lamp
Presentation title
A Wood’s lamp is a mercury vapor lamp that
emits longwave UV radiation generated by a
high-pressure mercury arc fitted with the “Wood’s
filter” made of barium silicate with 9% nickel
oxide. Wood’s filter is opaque to all light rays,
except a band between 320 and 400 nm with a
peak at 365 nm.
After absorption by a substance or tissue, the
emission of a longer wavelength light results in
visible fluorescence.
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20. Wood’s Lamp
20
Condition Colour of Fluoroscence
Tinea capitis (Microsporum genus) Blue-green
Pityriasis versicolor (Malassezia furfur) Yellowish-white
Erythrasma (Corynebacterium minutissimum) Coral-pink (because of coproporphyrin III pigment)
Hypopigmented and depigmented disorders Bright blue-white (margins appear accentuated because of contrasting effect of autofluorescence of
dermal collagen)
Hyperpigmented disorders Accentuation of contrast from normal skin in epidermal hyperpigmentation vs no change or diminution
of contrast in dermal pigmentation
Porphyria Red-pink
Acne vulgaris Orange-red fluorescence visible over comedones inhabited by P. acnes, because of the production of
coproporphyrin
Scabies Demonstration of the burrow by applying fluorescent substances like tetracycline or fluorescein
Photodynamic diagnosis of premalignant and
malignant conditions
Applying 20% ALA to the tumor for 4–6 h under occlusion

21. Dermatoscopy
Presentation title
A dermatoscope (dermoscope or
epiluminescence microscope or
episcope) is a noninvasive tool, which
visualizes the subtle clinical patterns of
clinical lesions and sub-surface skin
structures not visible to the naked eye.
21

22. Dermatoscopy
Principle
Physical properties of the skin influence
the outcome of light incident over it
(reflection, refraction, diffraction, and
absorption).
While the dry scaly skin reflects most
light, smooth oily skin allows penetration
till deeper dermis.
22

23. Dermatoscopy
Normal Dermoscopic Appearance
23
Site Colour/Pattern
Normal skin over trunk Fine reticulate pigmentary network
Normal skin over extremities Fine reticulate pigmentary network interrupted by
crisscross skin markings
Normal skin over the face Pseudoreticular Pattern
Upper Epidermis – S. Corneum – Spinosum Black
DEJ Light to Dark Brown
Papillary Dermis Slate Blue
Reticular Dermis Steel Blue

24. 24
When normal skin is stroked with a dull object, it becomes raised and inflamed to
assume the shape of the stroke. The response consists of local erythema followed
by edema and a surrounding flare reaction. Exaggeration of this response is
known as

25. Dermatographism
Triple Response of Lewis
1. Initial red line (capillary dilatation)
2. Axon-reflex flare with broadening
erythema (arteriolar dilatation)
3. Formation of a linear wheal
(transudation of fluid/edema)
Dermatographism usually develops
within five minutes of stroking the skin
and persists for 15- 30 min in contrast to
the normal triple response of Lewis that
subsides in less than 5-10 min
Time
The exact mechanism of
dermatographism remains uncertain but
it is likely to be caused by
‘mechanicoimmunological’ stimulation of
mast cells that release histamine.
25

26. Nikolsky Sign
Presentation title
The sign is best elicited by applying lateral
pressure with the thumb or fingerpad on skin
over a bony prominence. This results in a
shearing force that dislodges the upper layers of
epidermis from the lower epidermis.
A positive Nikolskiy sign indicates intraepidermal
cleavage and differentiates intraepidermal
blisters from subepidermal blisters.
It is pathognomonic of pemphigus and
staphylococcal scalded skin syndrome.
26

27. Bulla Spread Sign
Presentation title
Slow, careful and unidirectional pressure
applied by a finger to the bulla causes
peripheral extension of the bulla beyond the
marked margin.
The bulla thus extended has an irregular
angulated border in pemphigus vulgaris, while
a regular rounded border is observed in
bullous pemphigoid or other subepidermal
blistering disorders
27

28. Auspitz Sign
Presentation title 28
In Psoriasis, when the scales are completely
scraped off, the basement membrane is
exposed and is seen as a moist red surface
(membrane of Bulkeley) through which
dilated capillaries at the tip of elongated
dermal papillae are torn, leading to multiple
bleeding points

29. Carpet Tack/Cat’s Tongue Sign
Presentation title 29
In DLE, characteristic lesions are well
defined erythematous plaques with
partially adherent scales entering a
patulous follicle. When the scale is
removed, its undersurface shows horny
plugs that had occupied follicles

30. Thank You
Dr. Nishkarsh Chugh
PG Resident, Department of
Dermatology