Introduction to clinical dermatology
Structure,function,History and Examination and diagnostic
approach
Basic skin structure
• 2 layers: Epidermis and Dermis
• Epidermis: All Cells
• Dermis: variable
– Fibers: collagen and elastin – Ground substance
– Cells: Fibroblasts, Lymphocytes, Macro, Mast cells..
– Appendages: Glands ( sebaceous, Apocrine and Eccrine), Hair follicles and Nails
– Nerves, lymphatice, vasculature, smooth muscles
Epidermis 1 ALL CELLS
• 4-Cell layers (Keratinocytes):
– Basal layer: single row of columnar
epithelium. In normal skin cell mitosis takes place in this layer ONLY
– Prickle(spinous,squamous) layer: Several layers (5-8) of cells tightly bound by
Desmosomes. In cases where there is a problem involving Desmosomes cell
separation results (Acantholysis)
Epidermis 2
• Granular layer:
– 2 types of granules: keratohylin (Ptn)and Odland granules (Lipids and Hydrolytic enzymes)
• Horney layer (Stratum Corneum):
– Dead Cells (No Nuclei) called Corneocytes – This is the most important layer as Barrier
function of the skin depends on the presence of intact Horney layer
Basic Histology of skin
Epidermis 3
Proliferation and Desquamation
• In normal skin cell division only takes place within Basal cells
• 1/3 of Basal cells are dividing. 2/3 are resting
• The cell takes about 60 days to get from Basal layer to surface of Horney layer
• Hydrolytic enzymes from Odland granules
dissolve lipids cementing between corneocytes leading to desquamation of old degenerate cells
Epidermis 4 other cells
• Melanocytes: Dendretic
– Derived from neural crest – Within Basal layer
– Produce melanin which is then transferred to KC
• Langerhans cells: Dendretic – Skin tissue macro
– APC of both epidermis and dermis – Present throughout epidermis
• Merkel cells: non-Dendretic
– Transducers for fine touch – At Basal layer
Melanocytes and epidermal
melanin unit
Dermis 1
• Fibers:
– Collagen type 1 is the predominant type. Collagen 3 is mainly present in upper (papillary dermis). Elastin is found associated with Collagen bundles
• Ground substance: GAG
• Cells
– Fibroblasts: produce Fibers and Ground substance
– Mast cells: sore Histamine which upon release causes vasodilatation and Bronchoconstriction (anaphlaxis)
• Appedages:
• Nerves, vessels, muscles..
Skin as a Barrier
• The main function of skin to prevent entry of foreign things into internal environment
• Horney layer is the main structure responsible for this
• Problems and diseases affecting Horney layer will impair this function leading to
infections, allergies…
Skin immune system1 components
• Epidermal:
– Physical Barrier of Horney layer
– Langerhans’ cells:
• The main APC
• Has MHC-2
• Releases various mediators – Keratinocytes:
• Can become an APC
• Releases various mediators
• Dermal:
– Langerhans’ and other macrophages – T-Lym and other T cells
– Mast cells
Skin immune system2 immune reactions
• The interaction between skin immune
system and a foreign material results in an immune reaction
• This interaction takes place only if this
material penetrates into viable skin (defect
in Barrier) as immune cells are not present
within Horney layer
Skin immune system3 types of reactions
• Type 1 HSR
(Immediate type)
– If an ag interacts with IgE attached to a
Mast cells leading to release of Histamine and other mediators – Clinical examples
include Urticaria and Anaphylaxis
Skin Immune system 4 Immune rxns
2 • . Type 2 (Hummiral cytotoxic): IgG/IgM bind to tissue fixed antigen. This
activates complement system and damage
happens as a
result to inflammation Pemphigus and BP •
…
Skin immune system 5 Immune rxns
• Type 3 : Immune complex Disease: IgG Directed/binds to circulating antigrn/or other antibody: vasculitis and immune complex disease. The damage happens when immune complexes sit/deposit
usually in areas where circulation is tight or not moving enough: Kidneys, skin
capillaries and lower extrimities
Immune reactions 6
• Type 4 HSR (Delayed /celluar): this is the
only type where cells rather than antibodies are involved. The
cells are lymphocytes and macrophages.
Examples: ACD, Granulomas, ..
Derm. History 1
• Chief complaint +Duration:
– Rash: multiple red things with/out scale – Lesion: one or few things
– Others: as appropriate ( e.g hair loss, blisters, color change…)
Derm HX 2
• Analysis of the complaint:
– Onset : site where it started and how
– Progression: increasing/decreasing/same and which sites
– Modifying factors:
– Symptoms: itch, pain
– Recent illness: viral/fevers..
– Atopy: asthma+eczema+hay fever (personal or 1st degree relative)
– Drugs used
Derm HX 3
• R.O.S: Related
• Past Hx: as per others
• Family hx
• …
Derm Exam
• T. SAD:
– Type: primary vs secondary
(modified..scratched, traumatised…) lesion
• Macule/patch: pigmentary disorder or resolving papulosq
• Scaly papules/plaques: papulosquamous condition
• Non scaly papules/plaques: reactive erythema
• Bullae/vesicles: bullous dis….
Derm exam
– Shape: details of the primary lesion
• Color:
– red: more RBC.s(Hb) eithre intravascular(dilated vessels) or extravascular (hemorrhage)
– Brown/black: melanin
– Yellow: carotene (Horney layer and sc fat) – Exogenous….
• Surface:
– Scaly: papulosqumaous – Non scaly.
• Margins: well defined vs ill-defined (esp important for scaly rashes)
Derm exam
• Arrangement:
– Grouped: grouped vesicles (Herpes), Linear ( plane warts, Kobner…
• Distribution:
– Unilateral: infection, contact…
– Bilateral: inflammatory
– Hands/face:sun exposed
(photodermatpses/photoaggravated dermatoses).
Linear arrangmemnt
VEN
Plane warts
Grouping
Red NON-Scaly rash
• Red is BLOOD. This is either
– Intra vascular: dilated vessel due to usually
release of inflammatory mediators (histamine..) DIASCOPY……….BLANCHABLE
DDX: Reactive Erythema: EM/EN/URT - Extra vascular: Hemorrhage
- Vessel wall injury: vasculitis
- Bleeding tendency or due to trauma…
DIASCOPY……….NON-BLANCHABLE
Red NON-Scaly Algorhythm
Red non scaly
Red non scaly
Urticaria Time limit for Individual wheals
Of 24 hrs
Erythema multiforme Lesions for 1-2 wks
Acrofacial dist Target lesions
Erythema nodosum Lesions last 4-6 wks
Shins
Painful hot tender Nodules
.
Bruise like upon resolution
Patients with Red scaly rashes (papulosquamous)
• Scale is flake (piece) from horney layer.
• Usually indicates hyper-proliferation of epidermis
• The group includes many conditions but commonest are:
– Eczema - Lichen Planus
– Psoriasis - Fungal infections
-Pityriasis Rosea
Scaly rashes
Scaly bilateral and well defined margins. Extra features
:
Scaly,well defined ,
Bilateral
Psoriasis Commonest Salmon pink
Large silvery scales Extensor dist
Lichen planus Violaceous color Wickham’s striae
Flexors
Pityriasis Rosea Time limit 2-10 wks
Mother plaque Trunk dist (christmas
Tree/ribs )
Diagnostics
Wood’s light • KOH •
Diascopy •
Tzanck smear •
IF (Direct: tissue and Indirect: plasma )
Patch Test
Wood’s light
• Source of UVA (365 nm)
– diagnosis of some infections:
• Tinea capitis: green flu on hair shaft
• P. Versicolor: golden yellow
• Pitryosporum: orange
• Pseudomonas: blue
– Pigmentary disorders:
• Hypopigmentation (pale) vs Depigmentation (chalky white)
• Hyperpigmentation: good enhancement (epidermal/good prognosis) vs poor enhancement (dermal pigment/poor prognosis )
Diagnostic tools
Fungal Hyphae
Other diagnostic tools
Herpes Tzanck
Giant multinucleate cells
IF test The test is used to detect immune reactants (abs) directed against various targets so the test is used in conditions where abs are deposited e.g: Pemphigus, Pemphigoid
…
