Sunday, October 28, 2007

Skin Lesions by Dr. Azar Rsheed

SKIN LESIONS

(A) ANATOMY OF SKIN

SKIN: The largest organ in the body (16% of total body weight).

Composed of (i) Stratified cellular epidermis.
(ii) Underlying dermis of connective tissue resting on adipose hypodermis.


Epidermis: Approximately 0.2 mm thick. Five layers from within outwards.

(i) Stratum germinativum – (basal cell layer) – single layer of tall columnar, basophilic cells with large nuclei.
Scattered in between are dendritic cells (melanocytes) producing melanin.

(ii) Stratum Malpighii – (prickle cell layer or acanthotic layer) – Several cells deep. Polygonal, squamous cells sticking to each other by means of intercellular bridges called prickles (acanthus).

(iii) Stratum granulosm – rreansversely-lying cells containing keratophalin granules.

(iv) Stratum lucidum – clear zone found in palms and soles only.

(v) Stratum corneum (Horny layer)- several rows of anucleate, cornfiied cells. Average time taken by a cell from stratum germinativum to its loss from stratum corneum is 28 days.

Thickest on palms and soles and thinnest on eyelids. Acts as barrier to absorption

Dermis. Approximately 1.8 thick. Compsed of ground substance largely comprising of mucopolysaccharides. In its are scattered:
1. Cells e.g. fibroblasts (producing fibrinous collagen), mast cells (producing histamine) and histiocytes (reticulo-endothelial cells).

2. Fibres e.g. collagen, reticular and elastic. All from interlacing network giving strength and elasticity to the dermis.

3. Sweat Glands: (i) Eccrine – Found all over the body.
(ii) Apocrine – Found only in axillae, breasts and genital
region. Functional ast puberty.

4. Sebaceous Glands: Holocrine organs producing sebum.

5. Hair follicles with tangentially situated arrector pili muscles.

6. Blood vessels e.g. capillaries, arterioles and venules.

7. Lymphatics.

8. Nerves (i) Motor – Autonomic
(ii) Sensory – Free and encapsulated nerve endings.


SPECIALISED ECTODERMAL STRUCTURES: (Adaptation of horny layer).

1. Hair – Human body contains some five million hair follicles, number reducing with advancing age. Average rate of growth on scalp 3 millimeter per week. Three types:

(i) Lanugo – Downy, soft and unmedllated. Shed in utero.
(ii) Vellus – Fine, soft, unmedullated and unpigmented. Gradualy replaced after puberty by terminal hair.
(iii) Terminal – Longer, coarser, medullated and pigmented. Cycles of hair growth are asynchronous i.e. at a given time some hair are growing while others are resting or falling. One loses 50-100 hair/day normally from scalp. Total hair on scalp number 100,000 on average.

2. Nails: Formed from an invagination of epidermis situated on the dorsum of distal phalanx. Average rate of growth half to one mm/week. The toenails grow slower than finger nails.

(B) FUNCTIONS OF SKIN

1. Protection : Against mechanical, microbial, physical
or chemical injury

2. Water & Electrolyte : Through perspiration
regulation

3. Heat regulation : By means of sweating and variations in caliber of
blood vessels.

4. Perception : Of touch, pain and temperature.

5. Excretion : Of waste products e.g. urea, lactic acid.

6. Manufacture : Of Vitamin D.

7. Aesthetic : Attraction for the opposite sex.

8. Emotional : e.g. flushed in anger, pale in fear.


(C) TYPES OF SKIN LESIONS

(i) Primary – Those arising on normal skin.
(ii) Secondary – Superimposed on an already existing skin lesions.

1. Visible but impalpable alterations:

Macule : (Literally a spot) Change in the colour different from its
surrounding skin e.g. freckle.

Patch : Larger lesion of same sort e.g. melasma.

2. Palpable and usually visible alterations:

Papule : Lesion less than one centimeter in size having length.
Breadth and elevation e.g. lichen planus.

Plaque : Large lesion of same kind e.g. lupus vulgaris.

Nodule : Circumscribed swelling within the substance of the skin e.g. erythema nodosum.

Tumour : Large swelling e.g. squamous cell carcinoma.

Weal : (Derived from wale meaning lash): transient swelling due to oedema of the
dermis e.g. urticaria.



3. Wet or fluid containing lesions:

Vesicle : Fluid containing lesion less than 1 cm in size e.g. pemphigus vulgaris.

Bulla (Blister) : Larger fluid containing lesion e.g. pemphigoid.

Pustule : Pus containing lesion e.g. pustular psoriasis

Weeping : Exudation of fluid from the skin surface consequent upon the loss of superficial
part of the epidermis e.g. eczema.

Crust (Scab) : Produced by exudation of serum, blood or pus which then dries and sticks to the surface e.g. impetigo.


4. Lesions concerning stratum corneum:

Scale : Desquamating horny flake seen in conditions resulting in abnormal keratinisation e.g. psoriasis.

Exfoliation : Universal and continuous shedding of scales e.g. exfoliative dermatitis.

Hyperkeratosis : Hypertrophy of the stratum corneum e.g. chronic eczema.

Ichthyosis : Pattern on the skin surface fancifully resembling fish scales e.g. ichthyosis vulgaris.

5. lesions secondary to skin damage:

Excoriation : Mark, usually linear, produced by scratching e.g. pruritus.

Ulcer : Raw area resulting from loss of skin surface e.g. varicose ulcer.

Erosion : Superficial break in skin involving epidermis only e.g. pemphigus vulgaris

Fissure : Crack in the skin surface when it becomes thickened and inelastic e.g. chronic eczema.

Scare : Fibrous tissue replacement of normal skin often seen as an end result of many skin diseases e.g. burns.

Lichenification: Appearances resulting from thickening of the epidermis characterized by exaggeration of the skin markings and leathery appearance of the skin e.g. lichen simplex.

6. Lesions concerned with blood vessels:

Erythema : Redness due to dialation of blood vessels e.g. rosacea.

Telangiectasis : Pattern produced by permanently dilated blood vessesl e.g. radiodermatitis.

Purpura : Purplish red circumscribed spots due to leakage of blood into dermis e.g. anaphylactoid purpura. (Purpuric lesions do not fade on pressure).

Ecchymosis : Diffuse leakage of blood into dermis on a larger scale than purpura e.g. scurvy.
(Bruising)

Gangrene : Tissue necrosis often as the end result of deprivation of arterial blood e.g. peripheral vascular disease.


7. Special lesions:

Burrow : Seen only in scabies. Greyish, linear, C or S-shaped tunnel, formed by the female sacroptes in the upper epidermis, occurring in characteristics sites.

Comedo (Blackhead): Small black dot plugging the mouth of hair follicle e.g. acne vulgaris.

(D) HISTOPATHOLOGICAL TERMS

(i) EPIDERMAL CHANGES

(1) Hyperkeratosis: Increase in the thickness of stratum corneum.
(2) Parakeratosis: Retension of nuclei in the stratum corneum.
(3) Dyskeratosis: Premature keratinisation of cells.
(4) Granulosis: Increase in the thickness of the granular layer.
(5) Acanthosis: Increase in the thickness of acanthotic layer (Prickle cell layer).
(6) Acantholysis: Loss of intercellular bridges in the prickle cell layer resulting in free floating cells. Characteristically seen in pemphigus vulgaris.
(7) Spongiosis: Intercellular oedema of epidermal cells resulting in a spongy appearance.
(8) Basal Cell: Degenerative process of basal cell layer in which intra and
Liquefaction intercellular vacuolation occurs.
(9) Karyorrhexis: Fragmentation of the nucleus associated with cellular death.
(10) Pyknosis: Shrinking and condensation of the nucleus.


(ii) DERMAL CHANGES

(1) Vascualr : e.g. dilation, necrosis of the vessel wall, oedema.

(2) Cellular
infiltration: e.g. polymorphonuclear, lymphocytic, eosinophilic, histiocytic.

(3) Hypertrophy: e.g. keloid.

(4) Necrobiosis : Loss of nuclei in connective tissue with change in the normal staining
properties.
(5) Granuloma
Formation: Subacute or chronic inflammatory process in which the cellular infiltrate tends to form follicular masses.
(6) Deposits: e.g. fat in xanthomatosis, tattooing pigments.
(7) Tumour
Formation: Benign e.g. fibroma, neuroma, myoma, haemangioma, lymphangioma.
Malignant e.g. squamous cell carcinoma, basal cell carcinoma, melanoma, sarcoma.

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