skin infections 1 Flashcards
host defense
intact epidermis, acid pH, dryness, salty sweat, low surface temp
cidal props of skin: excreted chem compounds: sebum (FAs) and urea
phagocytosis by WBC
NF: Propionibacterium acnes, diphtheroids, staphylococci (coag-negative)
etiology of skin infections
non-infectious: allergic rxns, cancer, etc.
parasites and arthropods
bac, viruses, fungi
pathogenic patters of skin disease caused by bac, viruses, fungi:
systemic: blood-brn dis w. skin rash: (i.e. RMSF: rocky mountain spotted fever (Rickettia))
exotoxin mediated: TSS
*primary skin infection: bac, fungi, viruses (i.e. HSV most common viral agent)
exanthematous disease approach: progression and chronology are important:
where did it first appear?
chronology: how long has it been there and how has it changed?
Does it appear first on the limbs and then on the trunk or vice versa? Head first then spread down? Cheeks and torso?
did it always look like how it does now?
is there an enanthem or s/s of such?
is the enanthem present concurrently with the exanthem?
exanthematous disease approach: symmetry and anatomical distribution:
localized or regional or generalized?
where concentrated? (limbs, torso, head, face, etc)
exanthematous disease approach: description ?
ulcerative, pustular, petechial, macular, papular, vesicular?
pruritic? painful?
blanching? (fever + non-blanching rash: meningicoccal meningitis)
size
confluent or sparse?
color
exanthematous disease approach: associated s/s
concurrent fever? If not, when? before or after rash appeared? how long did it last?
is there a prodrome?
If so, does it occur with all age groups?
Is agent present in the lesions? IMPORTANT - Relates to transmission, is person
infectious?
Propionibacterium acnes: Acne Vulgaris
most common skin disease (not necessarily infectious disease)
initially caused by alteration in physiologic processes of sebaceous glands and hair follicle
If the sebaceous glands become colonized by P. acnes, an inflammatory, a self- limiting form of the disease occurs.
P. acnes
G+
non-motile
diphtheroid/pleomorphic rod
obligate anaerobe
virulence factor: extracellular Lipase
P. acnes epidemiology
predominant anaerobic member of NF of skin
most common contaminate in clinical specimen: blood and urine (is it causing the disease/infection or just there?)
Age - Teenagers (85% have acne) –> adults (persons [esp. women] in their 30s-40s). Direct cost $1 billion/yr.
Female>male but more scarring in males
pathogenic mechs: absence of P. acnes
increased sebum production occurs after puberty: follicular canal becomes plugged due to altered physiology
In absence of P. acnes: Get comedones
closed comedones “white heads”: Surface pore of the follicular canal is closed
Open comedones “black heads.”: Surface pore of the follicular canal is open, so air can enter in to oxidize material. Lesion with a central follicular impaction of lipid, keratin, melanin (which causes the easily observed brown or black appearance).
NFLAMMATORY LESIONS
- COLONIZED by P. acnes: (papules, pustules, nodules, cysts)
Proinflammatory mediators are FAs cleaved from sebum by lipase produced by P. acnes breaking down sebaceous gland secretions
first progress to papules then to pustules and nodules (cysts/cystic acne). Cystic acne associated with most of the scarring seen in acne.
P. acnes dx is usually obvious, but a number of disorders can be mistaken for acne: this ?? is helpful to rule out ??
and ?? can rule out ??
bacterial culture can be helpful to diagnose bacterial folliculitis (or Malazzia furfur)
skin biopsy will confirm or rule out granulomatous and neoplastic conditions
When signs of androgen excess are present in female patients, measurement of levels of ?? may be helpful
total and free testosterone, dehydroepiandrosterone sulfate, leutinizing hormone, and follicle- stimulating hormone
if PCOS is suspected, ?? can assist in confirming the diagnosis.
fasting glucose and insulin levels and pelvic ultrasonography
acne ddx
Malassezia folliculitis G- folliculitis Milia Perioral dermatitis Chloracne Favre-Racouchot disease Rosacea Herpes gladiatorum Tinea barbae CA-Staph aureus
Malassezia folliculitis
not limited to the usual acne sites (face, back, and
chest). It does not respond to typical acne therapies. Gram stain of pus from the lesions reveals gram-positive budding yeast
G- folliculitis
In patients on long-term antibiotics, superficial pustules or nodules can develop at the anterior nares and spread outward on the face; responds quickly to oral ampicillin.
