Dermatology



Dermatology






SKIN LAYERS










image



Epidermis



  • About 0.04 mm thick


Stratum Corneum (Horny Layer)

The outer most layer of the epidermis composed of dry, flattened, anuclear, dead, keratinized cells that ultimately flake from the body


Stratum Lucidum

A clear translucent layer of the epidermis


Granulosum Layer

Several layers thick; the cell’s cytoplasm contains keratohyalin granules.


Stratum Spinosum

Several cell layers thick; contains intercellular bridges, giving the cells a spiny appearance


Basement Membrane (Stratum Germinativum, Basal Layer)

Deepest layer of the epidermis composed of a single layer of rapidly proliferating cells that slowly migrate upward to ultimately become the stratum corneum. It takes 4 weeks for basal cells to reach the surface and be shed.


Dermis



  • About 0.5 mm thick


The dermis is the dense connective tissue stroma forming the bulk of the skin. It contains blood vessels, lymphatics, nerve ending, and hair follicles. The dermis is connected to the epidermis by finger-like projections called dermal papillae. These dermal papillae form ridges (fingerprints) at the surface of the skin.


Papillary Layer

Upper 1/3 of the dermis, contains Meissner corpuscles (light touch)


Reticular Layer

Lower 2/3 of the dermis, contains Pacinian corpuscles (vibration and pressure)


Subcutaneous Tissue (Panniculus, Hypodermis)

Composed of fatty connective tissue


ADDITIONAL CELLS


Melanocytes

Melanocytes produce melanin, which absorbs ultraviolet light and protects the tissue; they are in-termingled among the basal cells. Ultraviolet radiation activates melanocytes (tanning).


Langerhan Cells

Langerhan cells are dendritic cells (antigen-presenting immune cells) involved with the immune system. They are found throughout the epidermis, especially the stratum spinosum.


GLANDS


Sweat glands


Eccrine sweat glands

Distributed all over the body, most numerous in the palms and soles. They produce an odor-free watery substance and are involved in cooling the body. They open out onto the skin not in the hair follicle.


Apocrine sweat glands

Found abundant in the axillae and anogenital region, their ducts open into the hair follicles. They are adrenergic-mediated and produce a viscous sticky odorous substance.

Present at birth but don’t become active until puberty.


Sebaceous glands

Secrete sebum into the hair follicle and are located all over the body except he palms and soles. Oil glands found mostly on the face, neck, and upper body. Secrete sebum which is an oily, wax-like mixture of triglycerides and cholesterol. Secretes sebum by holocrine secretion whereby the entire cell content becomes excreted due to autolysis.


DERMATOLOGIC LESIONS


Primary Lesions

Bulla: Fluid-filled, elevated lesions over 0.5 cm in diameter

Burrow: An intraepidermal tunnel usually caused by insects or parasites

Cyst: Noninfected, deep-set collection of material surrounded by a histologically definable wall


Macule: Flat, circumscribed lesions measuring up to 1 cm in diameter. Cannot be felt, but can be seen.

Nodule: Circumscribed, solid, elevated lesion measuring up to 1 cm in diameter. Differs from a papule in that it has the added dimension of depth in the underlying tissue.

Papule: Circumscribed, solid, elevated lesions measuring up to 1 cm in diameter

Patch: Flat lesion measuring over 1 cm in diameter

Plaque: Circumscribed, thickened, elevated lesion over 1 cm in diameter

Pustule: A vesicle or bulla containing pus

Tumor: Circumscribed, solid, elevated lesion measuring greater than 1 cm in diameter. Differs from a papule in that it has the added dimension of depth in the underlying tissue.

Vesicle: Fluid-filled elevated lesions less than 0.5 cm in diameter

Wheal (hives): A well-circumscribed, elevated lesion that appears and disappears rapidly (minutes to hours)


Secondary Lesions



  • Changes due to evolution of the primary lesion

    Crust: Dried masses of serum, pus, or blood, generally mixed with debris—“scabs”

    Erosion: Deep excoriations in the epidermis, but the dermis is not breached, leaves no scars

    Excoriation: Scratch marks usually seen where there is pruritus

    Fissure: Linear, deep, epidermal cracks, commonly found in areas of dry or thick skin that may extend into the dermis

    Lichenification: Thickening of the skin with exaggeration of skin lines, giving a leathery appearance, often associated with hyperpigmentation. May be due to excessive scratching or rubbing.

    Maceration: Epidermis becomes overly hydrated and turns white.

    Scales: An exfoliative condition marked by flaking laminations of the epidermis

    Scar: “Cicatrix,” the formation of fibrous connective tissue, which has replaced dermis or deeper layer, lost as a result of trauma or disease

    Ulcer: Loss of the epidermis and a portion of the dermis

    Xerosis: Dry skin


DERMATOLOGIC TESTS


Auspitz Sign

Pinpoint bleeding that occurs when the scales of a psoriatic lesion are removed


Diascopy (Glass Slide Test)

Press a clear glass slide against the lesion and look for blanching. Dilated capillaries (erythema) will blanch, hemorrhagic lesions (purpura) will not.


Excisional Biopsy

Method of choice for diagnosis and removal of dermal and subcutaneous cysts and tumors
(epidermal cysts and lipomas) and also for malignant melanoma.

Can be used for lesions too big to punch biopsy.



KOH Test

A KOH test can be performed on hair, skin, or nail to diagnose dermatophytes.


Technique

Scrape the scales from a lesion onto a slide with a blade.

Apply a drop of 10% to 20% potassium hydroxide (KOH). KOH dissolves keratin so that the skin, nail, or hair shaft becomes clear.

KOH will dissolve keratin alone, but the process may be speeded up by adding gentle heat or DMSO.

Examine under microscope for the presence of fungus; if present, the septated fungal hyphae can be seen growing through the epithelial cells.


Nikolsky Sign

A skin finding in which the top layer of skin slips away from the lower layer when slightly rubbed. An epidermal detachment produced by lack of skin cohesion, seen in Bullous Diabeticorum.


PAS

Periodic Acid-Schiff stain test is a staining method for diagnosing fungus. PAS stains polysaccharides such as the carbohydrates found in the cell wall of the fugal hyphae. The cell walls of fungi stain magenta.


Punch Biopsy

Method of choice for most inflammatory or infiltrative diseases. Yields a full-thickness specimen of the skin.


Shave Biopsy

Particularly suited to lesions confined to the epidermis such as seborrheic keratoses or molluscum contagiosum


Small Nerve Fiber Biopsy

Tests the small unmyelinated nerve fibers (C fibers) in the skin. With small fiber neuropathy, neurologic exam, EMG, and nerve conduction studies may be normal because they test the large nerve fibers. The ideal biopsy site is the calf at 10 cm proximal to the lateral malleolus. Two standard tests are available:

Epidermal nerve fiber density (ENFD) test: Measures the density of the small nerve fibers in the skin

Sweat gland nerve fiber density (SGNFD) test: Measures the density
of the small autonomic nerve fibers in the sweat glands. SGNFD test is a more sensitive test for small fiber neuropathy than ENFD.


Tzanck Test

Used to diagnose viral disease (herpes simplex, herpes zoster, and molluscum contagiosum)

Technique involves scraping a fluid and base of vesicle or bullae onto a glass slide. The slide is fixed with methanol and stained with Wright stain. The presence of multinucleate giant cells suggests herpes infection.



DERMATITIS/ECZEMA


Contact Dermatitis

Dermatitis caused by contact with certain substances found in the environment causing inflammation of the epidermis and dermis. The most common and classic example of this is poison ivy. Another common cause is nickel, which is widely used in jewelry and in metal clasps on women’s underclothes. In podiatry, contact dermatitis is commonly due to the rubber found in the toe box of most shoes or the cement used to bind shoes together.


Classification



  • Irritation contact dermatitis

    Nonimmunologic mechanisms, whereby a single exposure causes a reaction (i.e., detergents, fiberglass)


  • Allergic contact dermatitis

    Acquired immunologic response. The first contact causes no reaction, but the exposure sensitizes the skin to future exposures (i.e., poison ivy).










image



Presentation

Irregular poorly demarcated patches of erythema and edema, on which are superimposed closely spaced vesicles, punctate erosions exuding serum, and crust. May be seen
with a subchronic or chronic lesion lichenification.



Atopic Dermatitis

Dermatitis resulting from a hereditary predisposition to a lowered cutaneous threshold to pruritus. This leads to scratching and rubbing that turn into eczematous lesion. There is usually a positive family history of allergic rhinitis, hay fever, asthma, or migraine headaches. Atopic dermatitis is often exacerbated by sudden changes in temperature, humidity, and stress/anxiety, and females may have eruption just before their menstrual period.


Classification



  • Infantile atopic dermatitis

    Usually starts at about 2 to 6 months and mostly seen on the face. In about half the infants, it clears up by age two and never returns; in the other half, it clears up and then reappears in late childhood or early teens (childhood atopic dermatitis).










    image



  • Childhood atopic dermatitis

    Starts in late childhood/early teens. Most commonly seen on the antecubital and popliteal fossae. In about half of these individuals, the condition clears up in adolescence; in the remaining half, it persists into adulthood (adult atopic dermatitis).


  • Adult atopic dermatitis

    As the person grows older, the rash usually seems to shrink and become localized. It can be found anywhere on the body but has a predilection for the flexures, front and sides of the neck, eyelids, forehead, face, wrists, and dorsum of the hands and feet.


Presentation

Irregular, often asymmetrical, poorly demarcated patches of erythema and edema, on which are superimposed closely spaced vesicles, punctate
erosions exuding serum, and crust. With a subchronic or chronic lesion, lichenification may be seen.



Urticaria

An allergic reaction resulting in transient pruritic wheals or small erythematous papules that erupt in minutes to hours and disappear usually within 24 hours or less. Patients often have a history of atopic dermatitis. In severe reactions, anaphylaxis may occur.










image



Causes

Food (milk, eggs, shellfish, nuts)

Drugs (PCN)

Parasites



Nummular (Discoid) Eczema

Pruritic dermatitis occurring in the form of coin-shaped plaques composed of grouped small papules/vesicles on an erythematous base. Especially common on the lower legs of older males during the winter. Lesions often have an associated bacterial infection, and treatment should include oral dicloxacillin or erythromycin in addition to topical corticosteroids.










image



Lichen Simplex Chronicum (Neurodermatitis)

A circumscribed area of lichenification resulting from repeated physical trauma (rubbing/scratching)











image



Stasis Dermatitis

Dermatitis of the lower leg related to PVD. Presents as erythematous scaling plaques with exudation, crusts, and superficial ulcers. Usually found just proximal to medial malleolus.

Symptoms include mild pruritus, pain, edema, and nocturnal cramps, and a painful ulcer may be present. Often associated with brown reticulated hemosiderin hyperpigmentation.



Dyshidrotic Eczematous Dermatitis (Dyshidrosis)

A special vesicular type of hand and foot eczema associated with pruritus. There is a predilection for the sides of the fingers, palms, and soles of the feet. Presents as small vesicles deep seated (appearing like “tapioca”) in clusters, occasionally bullae. Later stages present with scaling, lichenification, painful fissures, and erosions. Despite the name, sweating plays no role in the pathogenesis. There is a bullous form called pompholyx. Emotional stress and ingestion of certain metals (nickel, cobalt, or chromium) have been suggested as possible precipitating factors.



Seborrheic Dermatitis

A common chronic inflammatory disorder characterized by scaling and redness, usually worse in the winter. It does not cause hair loss.


Presentation

Flaky, white scales over erythematous patches. Most commonly seen in those 20 to 50 years; in children, it is called “cradle cap.”


Location of Lesions

Scalp, eyebrows, malar area, nasolabial folds, retroauricular creases, beard, presternal area, and central back. Less commonly seen in the axillae, groin, submammary area, and umbilicus.



Pyoderma Gangrenosum

A rare disease frequently associated with GI diseases (ulcerative colitis, Crohn dz). Consists of large ulcers with characteristic purple overhanging edges, which develop rapidly from pustules and tender nodules. Exact etiology is unknown; lesions occur particularly on lower legs, abdominal, and face. Responds to systemic steroids.










image




BACTERIAL INFECTIONS


Impetigo

A common contagious superficial skin infection seen in preschool children and young adults


Cause

Usually Staphylococcus aureus


Location of Lesions

Most often presents on the face, arms, legs, or buttock


Presentation

Initially presents as a red rash with many small blisters; the blisters later break, forming a crusted stage. In the crusted stage, there are golden-yellow crusts that appear “stuck on” an erythematous base.

Bullous impetigo presents as scattered thin-walled bullae arising in normal skin and containing clear yellow fluid without later becoming crusted.










image




Pitted Keratolysis

Superficial pitting in the stratum corneum on the soles of the feet, giving rise to a “moth-eaten” appearance. It is the result of a keratolytic enzymes produced by bacteria. Often associated with hyperhidrosis and bromhidrosis.


Cause

Corynebacterium or Micrococcus sedentarius










image





Erythrasma

A bacterial infection affecting the intertriginous areas of the body (between toes, groin, and axillae). There is a higher incidence in warm, humid climates and in diabetics. It often results as a secondary infection as a result of tinea.


Cause

Corynebacterium minutissimum



Presentation

Lesions are scaling, fissuring, and slightly macerated. In the feet, it most commonly occurs between the third and fourth toes, resembles tinea.



Cellulitis

An acute, severe, rapidly spreading skin infection (more specifically an infection of the connective tissue just beneath the skin). Any break in the skin can potentially result in cellulitis. Erysipelas—acute superficial form of cellulitis involving the dermal lymphatics.










image




Cause

Staph or Strep (most common pathogens are group A Streptococcus pyogenes and S. aureus)


Location of Lesions

Most common on the lower leg


Presentation

Sudden onset of tender, edematous erythema in an area of the skin that is warm to the touch as compared with the contralateral side. Spreads rapidly, and red streaking may be seen from the cellulitis toward the heart with swollen lymph glands nearest the cellulitis. If left untreated, sepsis can occur.



Folliculitis

A superficial contagious bacterial infection of a hair folliculitis usually caused by S. aureus. Most common on the neck, face, buttocks, and breast. Treatment involves applying moist heat to allow the lesion to come to a head and drain.










image

Only gold members can continue reading. Log In or Register to continue

Stay updated, free articles. Join our Telegram channel

Nov 20, 2018 | Posted by in ORTHOPEDIC | Comments Off on Dermatology

Full access? Get Clinical Tree

Get Clinical Tree app for offline access