General: benign epidermal proliferations caused by various papilloma viruses, common wart is called "verruca vulgaris"


Pathogenesis: dsDNA virus infects and replicates in keratinocytes, presence of virus stimulates epidermal thickening, still a lot to be learned!


HPI: child, young adult who is sexually active, skin lesion that can be painful, single or in groups


Risk factors: HPV infection, immunosuppression, meat handlers have higher incidence


Physical exam: papules/nodules that are flesh-colored, with a corrugated (shaped into alternate ridges and grooves) surface, may scale, will have interrupted skin lines with black puncta, often on hands and fingers


Types of warts: flat (slightly raised, flat-surface, well-marginated, often linear from autoinoculation), plantar (bottom of foot, often with callus), genital (condyloma acuminatum, soft/moist, sessile/pedunculated, cauliflower-like appearance, acetowhitening), types 6 and 11 cause genital warts, types 16 and 18 cause cervical cancers


Differential: callus (can use paring to distinguish; after paring warts will show interrupted skin lines with black puncta), carcinomas (ulcerative, refractory), comedones (smooth top), lichen planus (red-purple), corns (normal skin lines with translucent core), condyloma lata (genital syphilis, darkfield microscopy), seborrheic keratosis, Bowenoid papulosis

Histology: biopsy performed when suspicion for carcinoma is high, shows hyperkeratosis, acanthosis (thickened epidermis), within the granular layer will see vacuolated keratinocytes, koilocytes (large keratinocytes with small pyknotic nuclei surrounded by clear cytoplasm), upward extension of dermal papillae with capillaries


Complications: 35-65% resolve spontaneously within 2 years, main concern is carcinoma, types 16/18 highly associated with cervical and anal carcinoma, need to do pap smears in female patients, consider examining the sexual partner of the patient, *epidermodysplasia verruciformis = rare disease with diffuse, refractory warts due to HPV-5,8 that convert to squamous cell carcinoma*


Treatment: prevention is key; Gardasil vaccine protects against types 6, 11, 16, 18. Other than prevention, treatment aims to destroy keratinocytes infected with virus and can be quite painful. Treatment options = cryotherapy including 1-2 mm beyond margins + second freeze with follow-up useful for all warts; salicylic acid w occlusive tape for common and plantar warts; cantharidin for children (derived from blister beetle!); Retin-A for flat warts; 25% podophyllin resin for genital warts (toxicity, avoid during pregnancy); alternative treatments include 5-FU, interferon, biologics such as imiquimod 


References: AAD Basic Dermatology Curriculum, Dermatology by Bolognia et. al., Lookingbill and Mark's Principles of Dermatology, First Aid USMLE Step 1 2020, First Aid USMLE Step 2 CK

General: a benign tumor covered in epithelium with a dermal stalk 


Risk factors: middle-aged


Physical exam: tan or flesh-colored, small, pedunculated papule with a smooth surface, often in regions such as the axilla, groin, neck, eyelids, can have necrotic, crusty appearance if irritated 


Differential: nevi, neurofibromas (can be pressed in), carcinomas 


Histology: thickened epidermis with dermal connective tissue as a stalk, hyperkeratosis, papillomatosis, acanthosis, only need to send necrotic or large tags to lab  


Complications: cosmetic appearance, irritation, # can increase with age


Treatment: none necessary unless troublesome for patient, then (1) snip off with scissors or (2) cryotherapy


***Do not attempt to cut off a skin tag with scissors at home on your own! This can be dangerous and lead to bleeding and infection. Please see a dermatologist who can remove the tag safely!***


References: AAD Basic Dermatology Curriculum, Dermatology by Bolognia et. al., Lookingbill and Mark's Principles of Dermatology, First Aid USMLE Step 1 2020, First Aid USMLE Step 2 CK 

General: benign epidermal proliferation


HPI: gradually-appearing lesions later in life, slow-growing, patient may have scratched it off but it recurs


Risk factors: middle-aged adults, family members with similar lesions (autosomal dominant inheritance)


Physical exam: small, elevated, tan, brown, or black "stuck on" papules/plaques with a greasy appearance and well-defined margins, sometimes scaling, pedunculated, verrucous


Differential: actinic keratoses, warts, nevi (dermal growths), melanomas and carcinomas


Histology: can perform excisional or deep shave biopsy to rule out melanoma or carcinoma; you will see hyperkeratosis and pseudocysts (keratin-filled invaginations of the epidermis)


Complications: can become inflamed and form a lichenoid keratosis, can form more lesions with age, *Leser-Trelat sign: rapid increase in size and # of seborrheic keratoses along with pruritus can be a sign of malignancy involving the stomach or certain reproductive organs*


Treatment: none needed unless troublesome for patient, in that case (1) cryotherapy, (2) curettage


References: AAD Basic Dermatology Curriculum, Dermatology by Bolognia et. al., Lookingbill and Mark's Principles of Dermatology, First Aid USMLE Step 1 2020, First Aid USMLE Step 2 CK

General: infection of epidermal cells with poxvirus, most common in children


Pathogenesis: can spread by intimate contact, virus replicates within keratinocytes and forms large bodies in the cytoplasm, center of lesion disintegrates


HPI: pediatric patient with rash, adult with sexual history and genital lesions, patient with HIV/AIDS


Physical exam: smooth, small, flesh-colored, dome-shaped papules with central umbilication, can be single lesions or multiple, can progress to large number of lesions 


Differential: basal cell carcinoma (older patients, telangiectasia), central umbilication is key!


Histology: biopsy usually not necessary, but you can remove papule and crush onto a slide, will see molluscum bodies (sacs containing virions) and thickened epidermis 


Complications: lesions can persist for years or become inflamed, can involve eyes to cause conjunctivitis, dissemination in immunosuppressed patients 


Treatment: (1) spontaneous resolution within months, if not resolving (2) cryotherapy, (3) salicylic acid,  or (4) cantharidin (chemical blistering), *goal of treatment if necessary is to destroy the lesion*


References: AAD Basic Dermatology Curriculum, Dermatology by Bolognia et. al., Lookingbill and Mark's Principles of Dermatology, First Aid USMLE Step 1 2020, First Aid USMLE Step 2 CK

General: areas of friction/pressure that undergo epidermal thickening, very common 


HPI: patients have discomfort with walking or standing, maybe uncomfortable shoes, lots of barefoot walking


Physical exam: thick, brown/yellow or white/gray plaque or nodule, circular, well-circumscribed, horn-like, if one were to scrape the surface it would reveal a clear center with intact skin lines 


Differential: warts (may not have a central clearing with intact skin lines)


Histology: hyperkeratosis, thickened epidermal layer, however biopsy is unnecessary 


Complications: can persist, can get bursitis, infection, and even gangrene in at-risk patients (neurologic dysfunction from diabetes, arteriosclerosis)


Treatment: (1) paring with scalpel, (2) 40% salicylic acid  plaster to soften (keratolytic), (3) correct underlying cause of excessive pressure or friction, can also do surgery if anatomical skeletal deformity exists 


References: AAD Basic Dermatology Curriculum, Dermatology by Bolognia et. al., Lookingbill and Mark's Principles of Dermatology, First Aid USMLE Step 1 2020, First Aid USMLE Step 2 CK

General: second most common skin cancer, malignancy of keratinocytes in the epidermis


Pathogenesis: radiation, chemicals (arsenic), occupation exposures (soot, coal, tar), HPV alter cellular genetic material 


HPI: chronic skin lesion, not healing, occasionally bleeds or ulcerates 


Risk factors: sun/radiation exposure (geographic, occupational), carcinogen exposure, > 60 y/o male, lighter skin pigmentation, family/past medical history of skin cancer, 


Physical exam: hard, scaling, indurated, crusted, erythematous to flesh-colored patch/plaque/nodule, may bleed or ulcerate, often on sun-exposed areas (head, neck, arms), near scars or lesions, can involve mucous membranes and lower lip 


Differential: keratoacanthoma (rapid growth, central crater of keratin), basal cell carcinoma, seborrheic keratosis, wart, hypertrophic actinic keratosis, SCC in situ on the glans penis = erythroplasia of Queyrat


Histology: hyperkeratosis, abnormal keratinocytes, can invade dermis, can classify via grades 1-4


Complications: can metastasize (increased risk if > 2 cm, high grade, dermal invasion, location on ear/mucous membranes) through lymphatic system, SCC from AK has low risk of metastasis


Treatment: (1) reduce sunlight exposure (hats, long-sleeves, SPF 30 sunscreen, avoid mid-day sun), (2) excision, (3) electrodessication and curettage, (4) Mohs, could also try radiation


References: AAD Basic Dermatology Curriculum, Dermatology by Bolognia et. al., Lookingbill and Mark's Principles of Dermatology, First Aid USMLE Step 1 2020, First Aid USMLE Step 2 CK

General: common precancerous epidermal growths caused by sun exposure


Pathogenesis: UV radiation damages the DNA in keratinocytes, abnormal replication takes place and yields epidermal hyperplasia, dysplasia 


Risk factors: genetics, Caucasian, sun exposure (geographic region, occupation), lighter skin pigmentation


Physical exam: small, rough, scaling, reddish or brownish patch or papule, often on sun-exposed areas like the face, forearms


Differential: seborrheic keratoses (stuck on), carcinomas (larger, well-defined margins)


Histology: partial-thickness dysplasia of the epidermis, hyperkeratosis, parakeratosis 


Complications: indurated or stubborn actinic keratoses should be biopsied to rule out carcinoma, can progress to squamous cell carcinoma 


Treatment: (1) reduce sunlight exposure (hats, long-sleeves, SPF 30 sunscreen, avoid mid-day sun), (2) cryosurgery, could also use (3) topical 5-fluorouracil 5% twice daily for 2-3 weeks for multiple lesions (counsel patients that things will get worse over the next few weeks!)


References: AAD Basic Dermatology Curriculum, Dermatology by Bolognia et. al., Lookingbill and Mark's Principles of Dermatology, First Aid USMLE Step 1 2020, First Aid USMLE Step 2 CK

General: malignancy arising from basal cells of the epidermis, four subtypes (nodular, pigmented, superficial, scarring), most common form of cancer


Pathogenesis: cell in the basal layer of epidermis undergoes mutation causing unregulated growth, can be from insult (UV radiation, arsenic), genetic and involves the hedgehog pathway 


HPI: new growth that bleeds, history of skin cancer


Risk factors: sun exposure (geographic location, occupation), light skin pigmentation, lesions on nose or ear have high recurrence rate 


Physical exam: sun-damaged skin (freckles, wrinkles) in sun-exposed areas (head, neck), nodular type, most common,  presents as pearly, partially translucent papule/nodule with telangiectasia, waxy borders, and a central indention, often on the nose, pigmented type presents as a speckled, blue-black papule/nodule with a pearly margin, superficial type presents as a red, scaling, well-defined patch on the chest, often resembles eczema, can have a depressed center, pearly border, scarring type, most aggressive, presents as a white plaque resembling a scar with some crusting or erosion


Differential: sebaceous hyperplasia (yellow, central pore), nevus, seborrheic keratosis, melanoma, squamous cell carcinoma, dermatitis, look for non-healing and rolled borders, if there's doubt biopsy it!


Histology: uniform, blue-nucleus cells creating a thickened epidermal basal layer with involvement or budding into to the upper dermis


Complications: can become disfiguring, rarely metastasizes 


Treatment: (1) reduce sunlight exposure (hats, long-sleeves, SPF 30 sunscreen, avoid mid-day sun), (2) excision, (3) electrodessication and curettage, (4) Mohs, could also try radiation, cryotherapy, topicals like 5-FU


References: AAD Basic Dermatology Curriculum, Dermatology by Bolognia et. al., Lookingbill and Mark's Principles of Dermatology, First Aid USMLE Step 1 2020, First Aid USMLE Step 2 CK

Phototherapy: UVB 290-320, UVA 320-400,  can be used to treat skin diseases, such as psoriasis, can cause burns, cancer, and aging


Potassium hydroxide (KOH) mount: can diagnose dermatophyte infection via scraping of the edge of a scaling lesion and placing a drop or two of KOH w dimethylsulfoxide (DMSO) on the slide, blot, examine w low illumination, low power, looking for hyphae, can be difficult to find, can also use to diagnose candidal infection if you see hyphae/pseudohyphae 


Tzanck: can diagnose herpetic infection via scrapings from vesicular lesions, can see multinucleated giant cells, for herpetic viral infections can also do immunofluorescent staining


Scabies: can do a scraping of a suspected burrow and visualize the mite 


Cultures: scrapings, swabs, biopsies can be sent to assess for bacterial, viral, or fungal growth 


Biopsy: punch,  shave


Patch tests: used in diagnosing allergic contact dermatitis, patches left on the skin for 2 days 


Immunofluorescence: can detect autoantibodies to diagnose blistering disorders 


Mohs micrographic surgery: used for basal and squamous cell carcinomas of the skin,  layers are removed and examined one at a time to ensure all of the margins of a tumor are removed


Excision: gets tissue sample for study, can remove lesions, length 3x the width, use sutures to close 


Electrodessication and curettage: for removal of carcinomas, remove w curette and tx w electrode to destroy remaining cancerous cells


Cryosurgery: uses super cold liquid nitrogen, often used to tx warts or other common lesions such as seborrheic keratoses


With all surgeries and invasive procedures, make sure to get informed consent, discuss complications (neural damage, scarring, infection), discuss alternatives, and educate your patient on their condition! 


References: AAD Basic Dermatology Curriculum, Dermatology by Bolognia et. al., Lookingbill and Mark's Principles of Dermatology, First Aid USMLE Step 1 2020, First Aid USMLE Step 2 CK

General principles: 


- Vehicle (creams, lotions, oils, ointments, solutions, sprays, gels, foams, ointment can be higher potency than cream), concentration, amount, location, directions, expense, insurance, patient preference, generic versus brand name


- Topical therapy: directly to target, less systemic effects, difficult to apply 

- Patient's palm ~1% of their total body surface area, one fingertip unit ~500 mg used to tx 2% body surface area, thus two palms ~500 mg, takes ~30 grams to cover adult body, ~2 g for face or hands, ~3 g for an arm, ~4 g for a leg,  rule of 9's


- Characteristics of a prescription: generic/medication name, vehicle, concentration, use directions, amount, number of refills 


Dressings: protective coverings, dry dressings absorb drainage and can be nonadherent (for clean wounds) or adherent (for debridement/moist wounds),  wet dressings treat inflammation, astringent = drying agent, occlusive dressings promote wound healing, baths are wet dressings 

Topical steroids: anti-inflammatory, relief for burning or itching, class I (most potent) to class VII (least potent), hydrocortisone 1% ointment and desonide ointment 0.05% are class VI-VII, triamcinolone 1% ointment is class III-V,  fluocinonide cream 0.01% is low potency whereas fluocinonide ointment 0.05% is high potency, clobetasol ointment 0.05% is super high potency class I, *class determines strength not percentage*, class I best for severe scalp, palm, soles, thick lesions, class II-V best for mild-moderate, class VI-VII best for thin skin (face, genitals), intertriginous and large areas, side effects include acne, atrophy, striae, hypopigmentation, telangiectasias, dermatitis, rarely systemic effects such as Cushing's, HPA suppression, glaucoma, for duration use high potency ones for < 4 wks, medium potency < 6-8 wks, low potency in 1-2 wk intervals, when discontinuing treatment make sure to taper, be cautious of thin skin, pediatric patients have different body surface areas, use creams on weeping lesions, ointments for dry lesions, and gels or solutions on hairy areas, tachyphylaxis


Antibacterials: oral cephalexin for cellulitis, topical clindamycin for acne 


Antifungals: clotrimazole for tinea infections (except for tinea capitis, use griseofulvin or terbinafine)


Antivirals: acyclovir for herpes


References: AAD Basic Dermatology Curriculum, Dermatology by Bolognia et. al., Lookingbill and Mark's Principles of Dermatology, First Aid USMLE Step 1 2020, First Aid USMLE Step 2 CK