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L2
Diagnosis of Skin Diseases
D. Hadf
Learning objectives
By end of this lecture, the student should be able to:
o Identify the most common morphological presentations of skin lesions (primary &
secondary lesions).
o Be able to fully describe any skin lesion based on:
Shape
Arrangement
Color
Distribution
Morphology
Be familiar with the most important tools for investigations in dermatology
How to bring order to confusion:
What component is mainly affected? (dermis, epidermis, subcutaneous fat, blood
vessels)
What is the primary change and what is secondary?
Next assess the lesions by type, shape, arrangement, and distribution.
Finally, how did the changes evolve over time?
Types of lesions
Primary lesions
Secondary lesions
Special phenomena
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Primary skin lesions
They are the basic lesions with which the skin disease starts
ation less than 1 cm in diameter
flat circumscribed skin discolor
:
Macule
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A larger MACULE more than 1 cm in diameter is called A PATCH
They can be red, blue, white, brown
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3-
4
5
6
8-
Purpura
Visible, blood filled lesions in the skin, they are either:
a) petechiae: pinhead sized macules of blood in the skin.
b) Ecchymosis: larger extravasations of blood into the skin, as in many bleeding
disorders.
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Secondary skin lesions
These evolve from primary lesions during the natural progress of the disease, or may be created
by events such as scratching or infection.
They include:
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2)
Crust
: A collection of dried serum & cellular debris as in impetigo.
3-
Erosion
:
A focal loss of the epidermis, which does not penetrate deeper than the dermo- epidermal
junction, & so heals without scarring as in pemphigus.
4-
Ulcer
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5-
fissure
:
A linear slit in the skin with nearly vertical walls
as in finger tip eczema
6-
Sinus:
A cavity or channel that permits the escape of pus
or fluid as in pilo-nidal sinus.
7-
Excoriation
An ulcer or erosion, often linear caused by
scratching, as in neurotic excoriations
8-
Atrophy
:
A depression in the skin resulting from thinning
of the epidermis or dermis e.g. as a side effect of
topical or intra-lesional steroids.
9-
Scar
:
A result of healing where normal structures are permanently replaced by fibrous tissue, e.g. burn.
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10-
Lichenification
An area of thickened epidermis induced by scratching, the skin looks hyper pigmented
,thickened, with accentuation of skin markings, e.g. lichen simplex chronicus.
Special Phenomena in Dermatology
Koebner’s phenomenon
The tendency of the rash to appear at sites
of trauma, as in
Psoriasis
lichen planus
plane warts
acute eczema
vitiligo.
Nikolsky's sign
Sheet-like separation of the epidermis by gentle
traction as in pemphigus.
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Auspitz's sign:
Appearance of pin point dots of blood when
scales are forcibly removed in a psoriatic plaque.
Configuration of lesions
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OTHER AIDS TO DIAGNOSIS
1- DIASCOPY:
To differentiate erythema from telangectasia; press a slide firmly on the skin lesion, if a red
lesion blanches then it is due to vasodilation(blood inside the blood vessels), if not; it is purpura
(blood outside the vessels).
In TB of the skin diascopy reveals an appearance called apple- jelly nodules.
2- Dermoscopy
The lesion is covered by mineral oil or water, & observed by a hand held dermoscope, the fluid
eliminates surface reflection & make the epidermis translucent , used especially for pigmented
lesions as malignant melanoma ,also to identify scabies mites in their burrows.
3- Wood's lamp
A long-wave ultra violet light (360nm), a high pressure mercury lamp with a nickel-oxide &
silica filter, the patient should be put in a darkened room, & a special fluorescence occurs in
certain conditions which aids in their diagnosis:
Uses of WOOD’S lamp
1-ring worm of scalp: greenish fluorescence.
b) Erythrasma: coral red fluorescence in the flexures.
c) Porphyria : pinkish fluorescence of the teeth & urine of patients with porphyria cutanea
tarda
d) Pityriasis versicolor: Yellowish fluorescence.
e) Pigmentary disorders: Both in hypo & hyperpigmentation there is increased contrast,
as in vitiligo where areas of subtle depigmentation are more easily seen.
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4- MYCOLOGY SAMPLES
For fungal infection of skin, hair & nail
5- LAB. INVESTIGATIONS :
As hematological, biochemical, & serological Tests, together with Gram’s stain & culture for
bacteria
6- CYTOLOGY (Tzanck's smear):
Useful in blistering diseases, viral infections as herpes simplex & zoster, & in pemphigus
vulgaris
7- PATCH TESTS:
To document the presence of allergic contact sensitization (delayed hypersensitivity reaction) &
to identify the causative agents, in 24-48 hours eczematous reaction.
8- PRICK TESTS:
Used to detect type I (immediate) hypersensitivity reaction to various antigens as pollen, house
dust mite, or dander, in10 minutes. Wheal & flare
9- HISTOLOGY & IMMUNOFLUORESCNCE:
Ordinary H & E staining
In tumor cases, immunohistochemistry
Direct & indirect immunofluorescence in auto immune diseases
Mubark A. Wilkins