skin and nail infections and dermatitis

measles (rubeola)

Maculopapular, starts at hairline → face/neck → trunk/extremities; confluent

High fever, cough, coryza, conjunctivitis, Koplik spots (oral)

key features of measles

paramyxovirus

virus type of measles

togavirus

virus type of rubella

rubella (german measles)

Pink maculopapular rash, spreads face → trunk → extremities, faster than measles

Postauricular & occipital lymphadenopathy, mild fever, arthralgias

key features of rubella

Human herpesvirus 6/7

viral cause of roseola

Roseola (Exanthem subitum, HHV-6/7)

High fever 3-5 days, then sudden maculopapular rash (trunk → spreads out)

Febrile seizures, well-appearing when rash appears

key feature of roseola

Erythema Infectiosum (Fifth disease)

"Slapped cheek" rash → lacy reticular rash on trunk/extremities

Arthralgia (adults), aplastic crisis in sickle cell disease, hydrops fetalis in pregnancy

key complications associated with parvovirus B19

Varicella zoster virus (HHV-3)

viral cause of varicella

Varicella

Vesicular rash in crops at different stages (dew drop on a rose petal), centripetal (trunk > extremities)

lesions crust

varicella is contagious until

Coxsackievirus A16 (enterovirus)

viral cause of hand-foot-mouth disease

hand-foot-mouth disease

Vesicles on hands, feet, buttocks, painful oral ulcers

mononucleosis rash

diffuse maculopapular rash after antibiotics (esp ampicillin/amoxicillin)

Measles: rash progression slow, systemic symptoms severe.

Rubella: rash fades quickly, milder prodrome.

main difference in presentation of measles vs rubella

no

is the ampicillin rash in mono a true allergy?

impetigo

Superficial epidermal infection, most often by Staph aureus (MSSA, sometimes MRSA) or Strep pyogenes.

Non-bullous (most common): vesicles → honey-colored crusts.

Bullous: toxin-producing S. aureus, large flaccid bullae.

what are the two types of impetigo

bullous impetigo

Caused by toxin-producing strain of S. aureus, begins as red macules that progress to bullous (fluid-filled) eruptions on an erythematous base; after rupture, a clear, thin, varnish-like coating forms over denuded area; can be mistaken for cigarette burns

often requires systemic antimicrobial

post-strep glomerulonephritis (but not rheumatic fever)

most common complication of impetigo

Erysipelas

Raised, sharply demarcated erythematous lesion.

Classically on face or lower extremities.

Systemic signs: fever, chills often present.

Acute superficial dermal + lymphatic infection, usually caused by Group A Strep (S. pyogenes).

pathophys of erysipelas

cellulitis

Ill-defined, warm, erythematous, tender swelling.

Spreads rapidly, not sharply demarcated (unlike erysipelas).

Infection of dermis + subcutaneous tissue, most commonly by Group A Strep or Staph aureus

pathophys of cellulitis

erysipelas: superficial dermal and lymphatic infcection; sharply demarcated

cellulitis: invades dermis and subcutaneous tissue; not sharply demarcated

main differences between erysipelas and cellulitis

Can progress to sepsis, abscess formation, or necrotizing fasciitis.

complications associated with cellulitis

Infection of hair follicle, usually S. aureus.

pathophys of folliculitis

pseudomonas

hot tub folliculitis is caused by

folliculitis

Small erythematous papules/pustules centered on follicles.

Usually self-limited, but can progress to furuncle/carbuncle.

prognosis of folliculitis

Localized collection of pus within dermis or deeper tissue, usually S. aureus (including MRSA).

pathophys of abscesses

abscess

fluctuant, tender, erythematous nodule, may drain spontaneously.

Requires incision & drainage; antibiotics if severe, recurrent, systemic infection, or MRSA risk.

management of abscesses

Gentle cleansing and mild compresses help. Protection from offending substances and use of drying agents also help.

Topical application of clindamycin or erythromycin works well on mild casess. Bactroban may be used.

Extensive cases may require oral antibiotics

Hot tub folliculitis usually resolves without treatment. Severe or recalcitrant cases may be treated with a fluoroquinolone

treatment of folliculitis

Topical: mupirocin or retapamulin.

Oral (if widespread): cephalexin, dicloxacillin; clindamycin if MRSA suspected.

treatment recommendations for impetigo

Penicillin (oral or IV, depending on severity).

Alternatives: amoxicillin, cephalexin, clindamycin.

treatment for erysipelas

Mild: oral cephalexin, dicloxacillin.

MRSA risk: TMP-SMX, clindamycin, doxycycline.

Severe/systemic: IV cefazolin, ceftriaxone, vancomycin (if MRSA risk

treatment for cellulitis

Tinnea corporis

Annular, scaly plaque with central clearing and raised border.

Interdigital maceration, scaling on soles ("moccasin distribution").

presentation of tinea pedis

tinea cruris

ringworm of the groin (jock itch)

Patchy alopecia with scaling, "black dot" broken hairs. Common in children.

presentation of tinea capitis

onychomycosis

thickened, discolored, brittle nails

Beefy red rash with satellite lesions, moist intertriginous areas.

presentation of candidiasis of the skin

HSV 1/2

grouped painful vesicles on erythematous base, recurrent, prodrome of tingling.

HPV warts

verrucous papules/plaques, common on hands, feet, genitals

verrucous

warty, often rough surface

scabies

Presentation: intense pruritus (worse at night), burrows in interdigital webs, wrists, axillae.

permethrin 5% cream (entire body, repeat in 1 week), oral ivermectin in refractory cases.

treatment of scabies

permethrin 1% lotion/shampoo, repeat in 7-10 days. Alternatives: malathion, ivermectin lotion.

treatment of lice (Pediculosis capitis/corporis/pubis)

scabies: 5% cream

lice: 1% lotion

different concentrations of permethrin for scabies vs lice