Skin Flashcards
Strep is a gram ____, catalase _____, coagulase _____, _____ shaped bacterium in ______ (singlets/doublets/clusters/chains). Secondary tests?
Strep is a gram positive, catalase negative, coagulase negative (usually not done because irrelevant to dx), coccus shaped bacterium in chains. Sheep’s blood agar to see if alpha, beta, or gamma hemolytic.
These lesions have been recurring on a two-year-old’s neck and scalp for several months now. Describe by location/layer involvement, morphology, and likely histological findings.
Epidermal/spongiotic
Plaque
Mix of neutrophils and lymphocytes (acute-on-chronic), thickening of epidermis with significant sloughing of corneum, yeast/hyphae present throughout corneum and into hair follicles
Ringworm/tinea corpora/cradle cap
Patient presented to urgent care this morning with spontaneous blistering on the arm. Was recently started on lamotrigine with valproic acid for epilepsy. Blistering continued and patient was sent to ED. Quickly progressed to full-body involement. Describe by location/layer involvement, morphology, and likely histological findings.
Epidermal/spongiotic
Bullous (flaccid), diffuse
Significant eosinic involvement, neutrophils, serous exudate, detatchement and/or complete loss of skin
Steven J
Steps of PI3K pathway? Most common mutation in melanoma? Inhibitor?
Growth factor binds tyrk (tyrosine kinase)
Activates PI3K X—– PTEN inhibits (also a common mutation)
Phosphorylates AKT3 *** amplification mutation most common
Inhibits BAD (apoptosis) and activates FOXO1 (prosurvival)
SURVIVAL
Patient develops the following post major trauma. Non-gas producing. Becoming hypotensive, tachypnic, tachycardic. Dx, most likely microorganism, and relevant virulence factors? Tissue involvement? Next steps?
Necrotizing fasciitis with toxic shock
Group A strep
streptokinase (degrades tissue), speA and speB (shock), techoic acid (biofilms)
Full thickness, into muscle
SURGERY ASAP
What is/are antibiotic(s) of choice for MRSA?
Severe - IV only: Vancomycin (+ or - piperacillin/tazobactam) or daptomycin
Oral/less severe:
Clindamycin (lyncosamide, protein synthesis inhibitor)
Doxycycline or minocycline (protein synthesis inhibitor)
Linezolid (an oxazolidinone, protein synthesis inhibitor)
Trimethoprim/sulfamethoxazole (Bactrim or Septra) (folate synthesis inhibitor)
Patient presents to clinic for evaluation of new fatigue, thinks she might be menopausal. You notice that she is very freckled and ask about sun exposure. She says she doesn’t wear sunscreen but “doesn’t go out in the sun all that much”. You ask if she has any new freckles and she says that these two on her hand have been getting bigger. Describe by location/layer involvement, morphology, and possible histological findings. Next steps?
Epidermal, possible dermal involvement
Light brown macule with blurred borders, flat
Most likely: superficial spreading, pre-malignant melanoma. Melanocyte proliferation through epidermis, dysplastic, possible lymphocyte involvement.
Possible: benign macule/sunspot. No dysplasia, noticable accumulation of melanin/melanosomes but no noticable expansion of melanocytes.
Also possible: malignant melanoma. melanocyte proliferation past basement membrane and infiltrating dermis, with possible metastasis.
Next steps: biopsy, histo with melanocyte stain, CBC, CMP, general fatigue workup (menopause, hypothyroid, anemia…). If premalignant, complete skin evaluation and excisional biopsies, with photos and ongoing monitoring, counsel on sun protection. If malignant, scans etc…
These lesions have come and go for several years. Patient has rhematoid arthritis. Describe by location/layer involvement, morphology, and likely histological findings.
Epithelial/eczematous/spongiotic with likely dermal involvement
Papulosquamous, erethemetous plaques with scaling
Lymphocytes, thickened epidermis, poorly differentiated squamous cells in epithelium with retention of nuclei in corneum (excessive proliferation), excessive keratinization with sloughing, likely dermal involvement
Chronic (recurrent) plaque psoriasis
What are Merkel cells?
Nerves/touch receptors in basal membrane
Pt presents with the following. Patient has diabetes mellitus and is unhoused. Vitals are stable. Dx? Most likely pathogen? Relevant virulence factors? Tissue involvement? Next steps?
Abcess (multiple, severe)
Staph, strep both common
Staph: mecA (methycillin resistence), techoic acid (biofilm), catalase (tissue damage), coagulase (clots), possible TSST-1 (if shock sequellae)
Strep: techoic acid (biofilm), streptocydin (tissue damage), possible speA and speB (if shock sequellae)
Tissue involvement: appears to be full-thickness
Next steps: incision and drainage (likely in OR), IV abx (broad spectrum–>sensitivity test), agressive wound care (collagen or alginate dressings, possible hyperbaric), connect with social services/long-term care coordination
This lesion appeared after hiking a week ago. Describe the lesion by location/layer involvement, morphology, and likely histological findings.
Epidermal/spongiatic
Tense erethemetous vesicles
Eosinophilic infiltration, mast cells, plasma cells, epidermal detachment in some locations, serous exudate
Poison Ivy/Allergic Contact Dermatitis
What is the most common type of skin cancer?
Basal cell carcinoma
These lesions began appearing several months ago and more lesions are arising. They are raised, nonscaly, nonbullous, and smooth to the touch. Patient initially thought it was acne but no pus/popping, and the lesions have stayed in the same spot. Describe by location/layer involvement, morphology, and likely histology.
Dermal
Granulomatous/nodular
Granuloma = epethelioid macrophages with giant cells; surrounded by lymphocytes. Biopsy needed, not able to determine caseating vs noncaseating (sarcoid) based on clinical findings.
Sarcoidosis or tuburculoid (TB, leprosy). Suspicion for systemic involvement e.g. lungs in either case.
Steps of MAP-kinase pathway. Most common mutation in melanoma? Protein that inhibits this pathway?
Growth factor binds cKit
Ras activation X—- NF1 inhibits
Raf phosphorylation (activation) *** most common BRAF 600E
Mek phosphorylation (activation)
ERK phosphorylation (activation)
Transcription factor phosphorylation (activation)
PROLIFERATION
Patient presents to clinic for regular check-up. Points out new mole on hand. Describe by location/layer involvement, morphology, and likely histological findings. What specific cell marker could be used to help confirm diagnosis?
Multi-layer; epithelial origin, invasion past basement membrane into dermis, possible metastasis
Brown slightly raised macule with irregular borders
Extensive proliferation of melanocytes with invasion past basement membrane and into dermis, may be lymphocytic
S100 (a neural crest marker as melanocytes are neural crest derived)
Melanoma
What are Langerhan’s cells?
Macrophages in epithelium (usually stratum spinosum)
This lesion is warm to the touch and appeared 3 days ago. Describe by location (layer involvement), morphology, and most likely histological findings.
Epidermal/eczemetous/spongiotic
Scaly papules with erethemetous border
Neutrophil influx, epidermal thickening, basement membrane intact, no dermal involvement
Acute eczematous dermatitis
Staph is a gram ____, catalase ____, coagulase ____, _____ shaped bacterium in _____ (singlets/doublets/clusters/chains)
Staph is a gram positive, catalase positive, coagulase positive (Staph aureus) or negative, coccus shaped bacterium in clusters
Name some virulence factors for strep
speA and speB: toxic shock
M protein: molecular mimickry of myocin –> rheumatic fever (joint, muscle, heart problems)
Forms antibody-antigen complexes: glomerulonephritis
Techoic acid: biofilms
Streptokinase: necrotizing fasciitis
Name some virulence factors for staph
TSST-1: toxic shock
Catalase: digests tissue
Coagulase: blood clotting
mecA: methycillin resistance
Techoic acid: biofilms
Leukocydin: pokes holes in neutrophils (especially relevant in abcess)
Exfoliative toxin: scalded skin syndrome
Enterotoxin: heat-resistant food poisoning
What are the most common mutations in melanoma?
BRAF 600E gain of function mutation (proliferation via MAP-K pathway), AKT3 amplification (survival via PI3K pathway)
Also common: PTEN loss of function (loss of PI3K inhibition –> survival), Ras, NF1, triple WT (BRAF-, Ras-, NF1-)
These lesions have been persistent for a few months. They are non-bullous. Describe location/layer involvement, morphology, likely histological findings.
Interface (deep red/violet in light skin, dark brown/violet in dark skin)
Papules and plaques
Lymphocytes, some machrophages, dermal and epidermal involvement
(Lichen planus)
Which beta-lactam(s) can be used for MRSA?
Ceftaroline (5th gen cephalosporin)
Pipercillin/tazobactam does not work on its own but does show synergy with vancomycin
Patient presents with the following. Pt is an injection drug user. Pt is hypotensive, bradycardic, and bradypenic. Dx? Most likely pathogen? Relevant virulence factors? Tissue involvement? Next steps?
Cellulitis with toxic shock
Usually Staph aureus (strep also common)
—> high suspicion for MRSA in IVDU and other penetrating injuries
mecA (methycillin resistance), TSST-1 (shock), catalase (tissue damage), coagulase (clots)
Full-thickness
Next steps: aggressive emperic IV abx, treat shock, assist breathing, send cultures for sensitivity testing
Good abx candidates: Vancomycin, Pipercillin/tazobactam, meropenem/imipenem, linezolid
This rash appeared a few weeks ago. Patient has low-grade fever, fatigue, and general malaise. Describe by location/layer involvement, morphology, and likely histological findings
Interface (deep red/violet)
Papules and plaques, may be smooth or scaly
Lymphocytes, plasma cells, macrophages, dermal and epidermal involvement
Lupus butterfly rash
These lesions have been coming and going for years now, with this particular lesion being present for a few months. Describe by location/layer involvement, morphology, and likely histological findings.
Epidermal/spongiotic/eczematous with likely dermal involvement
Scaly plaques with excoriation and ulceration
Lymphocytes, macrophages, likely neutrophils due to excoriation, thickened epidermis, likely dermal involvement (due to chronic nature), lost epidermis/excoriation/ulceration in some regions
Chronic eczematous dermatitis with excoriation/ulceration
These lesions started appearing a few weeks ago, have spread but stay confined to a particular region of the body, and are extremely painful. Describe by location/layer involvement, morphology, and likely histological findings.
Epidermal/spongiotic
Tense vesicles and a few bullae (vesiculobullous)
Neutrophils and lymphocytes (intermediate duration), epidermal detachment in some places, serous exudate in epithelium
Along dermatomes
Herpes zoster/shingles
Steps of melanin production in response to UV?
UV exposure
DNA breakage
p53 activation
p53 –> DNA repair
p53 –> POMC (superhormone)
POMC –> beta-endorphin (happy) and alpha-MSH (melanocyte stimulating hormone)
alpha-MSH leaves keratinocyte and activates MCR1 (melanocortin 1) receptor on melanocytes
Stimulates production of melanin and transfer of melanosomes to keratinocyte
melanosomes accumulate on apical surface of keratinocyte
What is Sheep’s blood agar test used for? What dx distinctions between bacteria?
Hemolytic ability of strep strains.
Beta hemolytic = most hemolytic = group A (e.g. necrotizing fasciitis) or group B (e.g., strep throat)
Alpha hemolytic = somewhat hemolytic = pneumoiae (pneumonia or menengitis)
Gamma hemolytic = little to no hemolysis = mostly commensal
