Diseases of The Skin

The SKIN Is A Barrier

Layers of the Skin- 

Epidermis- Characteristics- stratified epithelium.  Stacks of cells.  Thicker in areas of wear and tear.  The bottom layers are actively mitotically.  As the cells on the top die, new cells are generated from below.  The upper layer is keratinized( water proofing).  No blood vessels. Separated by basement membrane

Dermis- Consists of connective tissue, fibers( reticular, collagen, and elastic) immune cells( mast cells and macrophages), fibroblasts, capillaries, nerve endings.  This is a thicker layer.  This layer also contains hair follicles, sebaceous glands, and sweat glands.  Fibers strengthen the integrity of the skin.  Protect the muscle layer below.  Serve as a filter for invading organisms

Subcutaneous - adipocytes( fat cells), blood vessels, fibers

Jay Doc Histoweb - http://www.kumc.edu/instruction/medicine/anatomy/histoweb/skin/skin.htm

1. Normal Microbiota of the Skin

a.  Microorganisms that grow on the skin have the ability to avoid drying out and dessication

b.  Like a salty environment

c.  Can grow on a surface

d.  Most of these are gram + bacteria

e.  These bacteria tend to clump together

f.  The bacteria on the skin communicate by quorum sensing - molecular messages. Antagonism can exist between microbiota

g.  Also present are gram positive pleomorphic rods called diptheroids

h.  Propionibacterium acnes are anaerobic and inhabit hair follicles( their growth is supported by secretions from the the sebacious glands.  These bacteria produce propionic acid. This maintains the low pH of the skin( 3-5)

i.  Another common diptheroid is Cornybacterium xerosis

j.  The yeast Pityrosporum ovule is capable of growing on oily secretions and is responsible for the scaly skin condition known as dandruff

( Shampoos that have anti- dandruff advertisements contain the antibiotic ketoconazole or zinc pyrithione or selenium sulfide.

Bacterial Diseases of the Skin

Staphylococcal skin infections

a.  Clusters of grapes

Coagulase + or Coagulase -

b.  Coagulase enzyme forms fibrin clot .  This represents a strategy for bacteria to avoid the immune system by creating an impenetrable wall around them.

Coagulase negative organisms are very common on the skin representing themajority of organisms that colonize the outer surfaces

c.  Coagulase negative bacteria are only pathogenic if the skin surface is cut into the dermis and those bacteria pass through the screening system of the immune cells in the dermis

d.  At one time all coagulase negative bacteria were thought to be

Staphylococcus epidermidis - They are now divided into several subspecies.

e.  Staphylococcus aureus is coagulase +.  These bacteria are protected from the phagocytes by the fibrin clot form around them.  They also produce leukocidin which destroys WBC.  They also can produce exfoliative toxin which can cause the skin to slough off.

scalded skin syndrome (analogous to scarlet fever)
Colonization: cell-bound (protein) adhesins
Invasion: staphylokinase, hyaluronidase and other extracellular enzymes (proteases, lipases, collagenase, elastase, etc.)
Resistance to phagocytosis: coagulase, leukocidin, hemolysins
Resistance to immune responses: coagulase, antigenic variation
Toxigenesis: Exfoliatin toxin

Enterotoxins also produced by these bacteria 

Staphylococcus is a nosocomial infection - it can be carried by hospital staff

 There is a problem with resistant forms of staphylococcus that do not respond to conventional drug therapy.

SPECIALIZED CONDITIONS

Follicultitis - Infection of the hair follicle

boils and pimples (folliculitis)
Colonization: cell-bound (protein) adhesins
Invasion: staphylokinase, other extracellular enzymes (proteases, lipases, collagenase, elastase, etc.)
Resistance to phagocytosis: coagulase, leukocidin, capsules
Resistance to immune responses: coagulase
Toxigenesis: cytotoxic toxins (hemolysins and leukocidin)

Pimples - staphylococcus aureus can enter the skin through eruptions in the skin

Furuncle- A serious infection around a hair follicle that fills with pus( Boil)

When the body fails to wall off a boil- damage can be done to surrounding tissue - this is called a carbuncle

Impetigo- thin walled vesices of the skin rupture and crust over - hexacholorophene - containing skin lotions are prescribed.

Toxemia- circulation of toxins

Scalded skin - toxin produced by a bacteriophage

Sty- Infected internal follicle of an eyelash   

Streptococcal Skin Infections   

a. Streptococci - gram positive spherical bacteria

b.  Secrete toxins and other moleules as they grow

c.  Streptococci produce hemolysins that lyse red blood cells

Beta hemolysis - complete hemolysis - clear halo

Alpha hemoloysis - partial -green halo         

Gamma - no hemolysis

Beta hemolysis- Streptococcus pyogenes

a. erypsipelas - skin erupts into reddish patches

b.  Streptoccous impetigo - school age kids - isolated pustules that rupture and then spread.  The bacteria can enter the skin through some minor abrasion or insect bite.  This is spread primarily through contact

Impetigo

c.  Streptococcal infections are usually localized.   They can cause other problems if they get below the epidermis - 

Invasive flesh eating bacteria -

http://www.ha.org.hk/qmh/micro/strept.htm

Pseudomonads

a.  Aerobic gram-negative rods that are widespread in soil and water

b. Capable of surviving in any moist environment 

c.  Most common is Pseudomonas aeruginosa  which is an opportunistic infection

d. Pseudomonas dermatitis -An infection of two weeks duration - This is often associated with saunas in which the water causes the follicles to open- the bacteria enter and cause a problem

e.  Otitis externa in individuals who are competition swimmers

f.  Pseudomonas is also a very serious problem with burn patients. Pus may produce a blue green pus called pycocyanin

 Burn patients and people with serious infections should not have flower vases in their hospital rooms.

g.  Resistance is a problem with pseudomonads.  Pseudomonads are sensitive to Pseudomonal Beta lactam antibiotics,( I was treated with silver sulfdiazine.  It was excellent and prevented a more serious infection when I was burned with turkey grease on Thanksgiving.

Acne

http://www.acne.org/myths.html

a.  Acne is one of the most common skin diseases in humans.  The most sever acne is cystic acne.

b.  Acne results when channels for sebum to the skin surface are blocked.  As sebum accumulates whiteheads form.  If the blockage breaks thorught he skin, balckheads form.

c.  Bacteria - Propionibacterium acnes an anaerobic diptheroid found on the skin has a nutritional requirement for the glycerol in sebum.  It forms free fatty acids during metabolic activities that in turn give rise to the inflammatory response characteristic of acne.  Oil based cosmetics can aggravate the condition.

Non prescription acne medications like benzoyl peroxide are effective against the bacteria  Benzymycin is a combinaton of erythromycin and benzoyl chloride.  This is effective for many

Accutane - This is a derivative of vitamin A which inhibits sebum formation and in most cases this results in an actual cure.

Viral Disease of the Skin

Human Papilloma Virus

http://obgyn.uihc.uiowa.edu/Patinfo/Adhealth/hpv.htm

Human Papilloma Virus

a.  Papillomas - Usually benign skin growths caused by viruses

b.  These can be transmitted from person to person by contact

c.  After infection there is a typical period of incubation before the warts appear

d.  They can be removed by treatment with liquid nitrogen( cryotherapy) or by electrical current( electrodessication) or by burning them with acid.

e.  The incidence of genital warts has reached epidemic proportions

Ringworm

Clinical signs result from penetration and digestion of the non-viable outer skin layer and of hair shafts by infective fungal elements. Often, there is some trauma to the skin, including bites from fleas, clipping wounds, etc. Arthrospores (the infective element) are present on the broken hairs, collars, and brushes from infected or carrier animals and contamination of the environment from these sources is common Arthrospores invade hair shafts and stratum corneum (the outer-most layer of the epidermis...see "SkinBasics" page).Some strains can also invade "living" tissue as well. Immune and inflammatory responses to organisms and their metabolic by-products contribute, in part, to the appearance of gross lesions (see below). In rare instances, an infected hair follicle may rupture and spread organisms to tissue beneath the skin (subcutaneous tissue) producing a firm, sometimes painful nodule known as a "pseudomycetoma". The disease is highly contagious, and Microsporum canis, the most common species in cats, is zoonotic, meaning that infections are transmissible to other species, including humans. (Not all dermatophyte species are transmitted between animals)

Story- Lost kitten to little boy

a.  http://www.astdhpphe.org/infect/ringworm.html

• Broken and brittle hair
• Partial or patchy hair loss
• Scales or crusts: primarily on the head and feet but lesions can appear anywhere, or everywhere (generalized dermatophytosis)
• Multiple scales, swollen or ruptured follicles on the chin and back:
  • that resemble lesions caused by flea and other allergies.
• Areas of self-mutilation:
  • one or more areas where inflammation or itching are prevalent

• Pruritis (itching): it may me non-pruritic or severely pruritic (resulting in self-mutilation)
  • unilateral or bilateral pinnal (outer ear) pruritis with scaling is another un(der) recognized presentation of Microsporum canis infection
  • miliary dermatitis
• Hair-Loss:
  • may be subtle or dramatic, symmetric or asymmetric, inflammatory or non-inflammatory
  • symmetrical alopecia may be seen in cats predisposed to dermatophytosis due to prior glucocorticoid administration or because the dermatophyte, itself, produced a symmetrical pattern of alopecia
• Crusting and Scaling:
  • lesions are usually exfoliative
  • in some cats scaling is severe…it could resemble Pemphigus foleaceus
  • mounds of thick, adherent crust may accumulate on the face, ears, nail beds especially on long-haired cats
  • erythema and scaling of inner and/or outer ear (with pruritis)
• Comedo-like ("blackhead-like") lesions:
  • chin acne in young cats
• Hyperpigmentation (darkening of skin):
  • this is an uncommon clinical finding in cats in general; however when it is present, it is most likely due to dermatophytosis
• Paronychia:
  • crusted or exudative paronychia (inflammation of nails) may be the only sign of dermatophytosis in some cats
• Erythema (reddening): is a common finding is early lesion…and is often accompanied by hair loss
• Eosinophilic plaque: usually due to allergy, but can occur secondary …to pruritic Microsporum canis lesions
• Military dermatitis (multiple scales, crusts, scabs, papules):
  • these lesions may be seen after clipping (due to trauma of clipping?).
  • is a form of folliculitis
• Indolent ulcer:
  • these are red, raised, glistening lesions around mouth usually
  • there is evidence that M. canis is an unrecognized …cause of this
• Granulomatous lesion:
  • may present ad non-healing wounds or nodules (especially in long-haired cats)
• Miscellaneous:
  • facial folds and periocular (around eyes) hair
    • most common when treated with lyme-sulfur dips, because owners are reluctant to apply this obnoxious dip to face
    • animals also have facial-fold pyoderma (superficial skin layers are infected), conjunctivitis and blepharitis
       
• Varied lesion distribution:
  • may be focal (in one place) or multifocal (in more than one location)
  • even if focal, spores will be present throughout the coat, due to grooming
  • in young kittens:
    • Scaling and alopecia on the face, ears, muzzle and forelimbs
  • in older kittens and young cats:
    • Irregular patches of alopecial with or without crusting
• Other signs:
  • "excessive shedding" (is a common complaint)
     
  • constipation, vomiting (from hairballs)

 

• Atypical: Rarely, infection extends to the deeper (subcutaneous) tissues and a painful, inflammatory lesion follows.

b.

c.

. 

d.

KOH Treatment