Infectious Disorders Flashcards
Where do dermatophytes survive and what is tinea manuum?
They infect and survive only on keratinized tissue (i.e. skin, hair, and nails) and thus fail to survive on mucosal skin which does not have a keratin layer
Tinea manuum = tinea of hands
Is tinea versicolor a dermatophyte infection?
No, it is caused by a yeast-like fungus called Malassezia furfur which is potentially more invasive than the dermatophytes.
Also called pityriasis versicolor
What might tinea capitis be confused with and how do you differentiate it from those entities?
Confused with psoriasis or seborrheic dermatitis, because it appears as a diffuse, fine, white adherent scale on the scalp
Differentiated by presence of “black dots” which are broken hair shafts, as well as hair loss, which is not typically seen in those other two conditions
What is kerion? What are the complications?
The boggy, inflamed, postular appearance of the scalp in a severe inflammatory response to tinea
Can lead to scarring and permanent hair loss. Often associated with lymphadenopathy
How is tinea capitis diagnosed and treated?
Diagnosed via KOH prep which shows spores in or around hairshaft
Treatment: oral griseofulvin or terbinafine is required
Adjunctive therapy with ketoconazole shampoo may be used
Who gets tinea corporis and how does it appear?
Typically pre-adolescents
“Ringworm” - Appears as an erythematous patch with raised, scaly borders. There is often a central clearing.
Who gets tinea cruris and what area is usually spared?
Usually in post-pubertal males who are sweaty and obese
It will be bilateral, advancing to thighs and buttocks, but usually spares the scrotum.
What is the most common tinea infection and what are the three subtypes, and which of these is most common?
Tinea pedis - “Athlete’s foot”
- Interdigital - most common, between toes
- Moccasin distribution - lateral borders of feet/soles
- Acute vesicular - difficult to differentiate from dyshidrotic dermatitis
What is the common presentation of tinea manuum?
Two feet, one hand:
Often presents secondary to pre-existing tinea pedis, as patches with fine scaling appear on palm of dominant hand due to touching tinea pedis.
What is tinea incognito? How does it appear?
It is tinea which looks abnormal due to misdiagnosis and usage of topical corticosteroids
- > rash flares with withdrawal of steroid
- > rash is often disseminated, lacking scale or raised border
What is tinea unguium also called, and what are the risk factors?
Onychomycosis
Risk factors: increasing age, immunosuppression, diabetes, poor circulation
How does tinea unguium appear and what is on the DDx?
Thickened, discolored nail plate with onycholysis (splitting apart) and subungual hyperkeratosis
DDx:
Psoriasis
Chronic trauma
How is tinea unguium diagnosed and treated?
Diagnosis: KOH prep, or nail clipping for PAS staining (Very quick but shows dead fungus). Gold standard is fungal culture.
Treatment: Long course (12 weeks) of oral terbinafine which is hepatotoxic, so rarely done
When does tinea versicolor usually happen and what parts of the body are favored?
Usually during the summer months (hot, humid weather) with high sebaceous gland activity
- > malassezia furfur loves oil / lipids
- > especially occurs in upper trunk and arms
Where in the skin does Malassezia furfur live, and what will the rash look like?
Lives in the stratum corneum, looks like small, circular hypopigmented (not depigmented like vitiligo) patches with fine scale
What does Malassezia furfur look like on KOH prep and what should the treatment be?
Spaghetti and meatball yeast and pseudohyphae forms
Treatment: Oral azoles, with recommendation to sweat 1 hour afterwards (increase sebaceous gland concentration), also selenium sulfide (Selsun blue)
What are the risk factors for candidal intertrigo?
Obesity, diabetes (think of candy jar in sketchy), pregnancy / OCPs (think of BCP in sketchy), antibiotic use (think of jar of pills in sketchy)
How does candidal intertrigo appear and what areas are involved?
Appears as moist, erythematous, macerated plaques in warm areas (skin folds)
Often pustules around periphery
Can be distinguished from dermatophyte infection via involvement of scrotum
What is angular cheilitis a possible presentation of in children? What can predispose children to it?
Oral candidiasis -> painful, red scaly macules and fissures on oral commissures
Children predisposed by lip-licking -> saliva forms a warm environment for candidal growth
How does primary HSV infection generally present in children?
Fever, malaise, regional lymphadenopathy, and gingivostomatitis.
May also allow for a secondary infection with S. pyogenes/aureus -> impetigo.
How does genital herpes tend to present?
Vesicles grouped on an underlying erythematous base, but they pop easily and tend to present as superficial erosions and ulcerations
What is herpetic whitlow and who gets it?
Herpes on fingers of kids who suck them, or healthcare workers
What type of HSV is associated with TORCH infections? What are the clinical manifestations?
HSV-2, passed via mucous membrane contact during delivery
Manifestations: meningoencephalitis, herpetic vesicular lesions which are widespread
What are the characteristics of the VZV (chickenpox) rash? Are the lesions all at the same time? What is the lesion progression?
Vesicular rash which begins on the trunk, spreads to face and extremities.
Lesions are all at different stages (ALL ages welcome)
Macule -> papule -> dew drop on a rose petal -> pustule -> crusting / scabbing over
Is the vesicular fluid of shingles vesicles contagious?
Yes -> could be a problem for adults taking care of young children
What is Hutchinson’s sign as it relates to VZV? What should be done?
Vesicles on tip of nose heralding ocular VZV infection -> means the nasociliary branch of V1 is affected, ophthalmology should be consulted to prevent eye involvement leading to blindness
What is the definition of disseminated Zoster?
Skin lesions outside of affected dermatome + 1 dermatome adjacent each way.
When should the shingles vaccine be given?
Given if greater than 60+ years old, can be given 3-6 months after VZV flare after active lesions are crusted
What do Molluscum Contagiosum lesions look like and how are they spread?
Pearly-pink dome-shaped papules with central “umbilication” which is dimpled, seen on trunk, face, and groin
Spread sexually typically, but can also be spread in children by direct contact and then hand to groin transmission elsewhere in the body
What causes verruca vulgaris and where is it typically found?
HPV, typically found on the hands as hyperkeratotic, cauliflower-like papules.
What do you call the following processes of HPV:
- Endophytic papules affecting plantar surface of feet which may form confluent mosiac warts.
- Small, flat-topped papules with minimal scale seen on face and hands
- Verruca plantaris - on feet
2. Verruca plana - flat-topped on face and hands
Are HPV 16, 18, 31, and 33 responsible for genital warts? How are they spread?
NO, typically genital warts (condyloma acuminata) is caused by HPVs 6 and 11
These are the carcinogenic HPVs, typically spread via asymptomatic shedding.
What are a couple treatments for genital warts?
- Salicylic acid
2. Liquid nitrogen cryotherapy
What is impetigo and what is its classic appearance?
A very superficial skin infection which is limited to the epidermis
Classical appearance: erosion with honey-colored crust (from pustular exudate following pustule bursting)
What organisms typically cause impetigo?
S. aureus more commonly than S. pyogenes
Bullous impetigo in particular is caused by S. aureus
What type of bulla are seen in bullous impetigo and what causes it? What skin level is affected
Flaccid bulla - caused by exfoliative toxins secreted by S. aureus
-> intraepidermal cleavage within stratum granulosum
What is cellulitis and what agents typically cause it?
Acute, painful, spreading infection of the deep dermis and subcutaneous tissues
Usually caused by S. pyogenes or S. aureus
What systemic symptoms typically accompany cellulitis? How will the lesion appear?
Fever, chills, regional lymphadenopathy.
-> area will be warm, red, tender, and swollen. Think rubor, calor, tumor, dolor
What are risk factors for development of cellulitis?
Skin trauma, leg ulcer, tissue web fissure (especially random gram negatives), animal / insect bites, recent surgery, diabetes
What typically causes crepitant vs necrotizing fasciitis? What physical exam finding is characteristic of the latter?
Crepitant - gas gangrene: Clostridium perfringens
Necrotizing fasciitis - Group A strept, MRSA, or polymicrobial
Necrotizing fasciitis is due to deep tissue injury. Pain will be OUT OF PROPORTION to physical exam findings.
How is stasis dermatitis told apart from cellulitis?
Stasis dermatitis - erythema / swelling / warmth due to poor vascular circulation and venous insufficiency
-> CAN be bilateral
Cellulitis - almost NEVER bilateral
What infectious disease commonly causes painful erythema surrounding the anus in children?
S. pyogenes -> perianal strep in children
What toxins from both S. aureus and S. pyogenes is associated with toxic shock syndrome / toxic-shock like syndrome? How do they work?
S. aureus - TSST-1
S. pyogenes - Exotoxin A
Both work by binding MHC II to TCR outside of antigen binding, causing release of inflammatory cytokines and shock
What are the symptoms of TSS and which bacteria has the worse prognosis? How should patients be treated?
Fever, rash, shock, often associated with prolonged tampon use.
Can lead to skin desquamation and rash which will require supportive IV fluids and potential treatment in burn unit
S. pyogenes is roughly 10 times more deadly than S. aureus in this instance
What does primary syphilis present with?
Chancre occurs at site of inoculation:
Red macule -> papule -> non,tender ulcer with raised border. Can be regional lymphadenopathy nearby.
What are the manifestations of rash in secondary syphilis? Include full body, genitals, scalp, and mouth.
Papulosquamous rash -> pink to red-brown macule on face, trunk, palms, and soles
Condylomata lata - warty papules in anogenital region
Moth-eaten alopecia of scalp
Split papules on lateral commissures of mouth.
What is RPR/VDRL testing for? Why might it be preferred over the specific test?
RPR/VDRL test for nonspecific antibody that reacts with beef cardiolipin. It can give a false positive in lupus. Can be used to check for disease activity since it will go down once infection is cleared.
FTA-Abs is sensitive for ever having had syphilis before, but will not return to normal.
Are primary and secondary syphilis lesions both infectious?
Yes, they both are. Only tertiary is not infectious (they are due to host immune response)
What are the early and very late stage rashes seen in Lyme disease?
Early - Erythema migrans - bullseye rash
Late - Acrodermatitis Chronica Atrophicans -> chronic skin atrophy leading to prominent veins
What causes scabes and what are the symptoms which will be experienced by the patient? When is it worse?
Sarcoptes scabiei, symptoms are pruritis starting 2-6 weeks after exposure and patient has sensitized to mite and its feces (scybala)
-> itching is much worse at NIGHT
What is the pathognomonic lesion of scabies? Where do people tend to be affected?
Linear or curved burrow (serpiginous) in webspace of hands / feet
People tend to be affected in hands, feet, and genitalia
Face and scalp generally affected in infants but spared in children / adults
What is Crusted Norwegian Scabies? What are the symptoms?
Condition affecting immunocompromised, elderly, and debilitated individuals
-> thick scaly plaques which are not very pruritic, but are HIGHLY infested with mites which are HIGHLY contagious
What is the treatment for scabies?
Permethrin cream, treatment of close contacts, washing / bedding
What are lice? What is the condition called?
Blood-sucking, wingless insects which are obligate human parasites
Condition is called pediculosis
How long can lice live off the body?
Head lice - 36 hours
Pubic lice - 36 hours
Body lice - 10 days
-> responsible for epidermic typhus and louse borne relapsing fever
What is the treatment for lice? What should you do about the nits?
Once: Pyrethroids, malathione, ivermectin, permethrin. Then repeat in 1 week because younger lice and nits may not be eradicated.
Make sure to comb out the nits (small white eggs on hair shafts which are generally close to the scalp)
-> not doing this is the biggest reason for treatment failure
What should be done with clothing and furniture in lice?
Wash in hot water for 10 minutes
Articles which cannot be washed must be sealed in a plastic bag for 3 days for head / groin lice, and 2 weeks for body lice (obligate human parasites)
What materials to bed bugs (Cimex spp.) infest? How do they cause symptoms?
They hid in mattresses, wood furniture, books, and paper
-> Saliva injected into host at time of feeding, anticoagulant leading to welts and itching
What pattern of bites will bed bugs show?
Breakfast, lunch, and dinner pattern
-> you can’t feel their bit, so they will bite you multiple times in a row without you noticing, walking in a line and biting your skin
