Diagnosis of Skin Diseases

Diagnosis of skin diseases

By end of this lecture the student should be able to:
• Identify the most common morphological presentations of skin lesions (primary & secondary lesions).
• 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

The key to a successful Rx is a correct Dx

Dermatological diseases are usually visible, so inspection is all that is needed for Dx
Keen eyes

Magnifying lens

Correct diagnosis

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

Primary skin lesions

They are the basic lesions with which the skin disease starts

1-Macule: flat circumscribed skin discoloration less than 1 cm in diameter

A larger MACULE more than 1 cm in diameter is called A PATCH
They can be red, blue, white, brown

2---

3-










4- Nodule : A larger & deeper lesion than a papule, e.g., erythema nodosum, neurofibromatosis.

5- Blisters

A circumscribed elevation of the skin containing fluid, of 2 types:
A) vesicle: less than 0.5 cm. in diameter e.g. acute dermatitis.
B) Bulla: larger than 0.5 cm, e.g. pemphigoid .


Eg of vesicles

6- pustule: A visible accumulation of pus, as in folliculitis.

7-

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.


E.g. of petechiae & ecchymosis









9-

10-

11- Telangectasia : Permanent visible dilation of superficial blood vessels in the skin as in rosacea





12- Comedo: A plug of keratin & sebum wedged in a dilated pilo-sebaceous follicle, there are 2 types; open (black heads) & closed (white heads), as in acne vulgaris.

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:

1-Scale: Excess flakes of dead epidermal cells from the horny layer, could be mild as in chapping or severe as in psoriasis.

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 impetigo,
& pemphigus.

4-Ulcer

A focal loss of epidermis &
dermis & so heals with
scarring as in primary
syphilis.

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.

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.

lichenified palques

Old trees

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




Auspitz's sign:
Appearance of
pin-point
dots of blood when
scales are forcibly removed in a psoriatic plaque

Configuration of lesions

Annular: T. corporis, granuloma annulare
Round/ Discoid: nummular eczema, discoid lupus
Polycyclic: urticaria, SCLE
Arcuate: urticaria
Linear: scabies burrow, Koebner’s phenomenon
Reticular: livedo reticularis

Serpiginous: cutaneous larva migrans

Targetoid lesions: erythema multiformi
Grouped/herpitiform: HSV
Zosteriform: herpes zoster
Scattered: chicken pox


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.

Wood's lamp

A long-wave ultra violet light (360nm),

obtained by 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

A) 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.

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
& to identify the causative agents. A battery of 20 antigens are
Applied to the back of patients
& examined in 24-48 hours,
any eczematous reaction
would suggest a delayed
hypersensitivity reaction
to this substance

8) PRICK TESTS:

Used to detect type I (immediate) hypersensitivity
Reaction to various antigens as pollen,
house dust mite, or dander, the
Skin is pricked with the antigen
& examined in 10 minutes
a wheal & flare would suggest
a positive reaction

9) HISTOLOGY & IMMUNOFLUORESCNCE:

Ordinary H & E staining
In tumor cases, immunohistochemistry
Direct & indirect immunofluorescence in auto immune diseases