USMLE Step 3 Dermatology


  • Malignant melanoma:
    • signs of malignancy include irregular borders, increasing in size, odd colors.
    • They are generally more than 5 mm in diameter.
    • Excisional biopsy is the FSOM to confirm the diagnosis and stage the lesion.
    • Eventually, if it is melanoma, you’ll want to do a complete excision, which is curative a lot of the time.
  • Melanoma:
    • Majority of melanomas are associated with excess sun exposure.
    • It happens more often in fair-skinned people, and usually develops in areas of the body that are intermittently exposed to
      intense sunlight.
    • Should wear protective clothing when exposed to the sun.
    • Sunscreen can reduce the incidence of basal and squamous cell cancer, but no evidence it helps to prevent melanoma.
  • When hairs have split ends,
    • it means that there is a toxic/chemical reaction causing the hair loss.
    • Numerous drugs can cause hair loss (ex Li, thallium, chemo) but they do not affect the hair shaft or produce split ends.
  • Psoriasis:
    • an inflammatory skin disorder characterized by hyperproliferation and abnormal differentiation of the epidermis.
    • There are sharply demarcated erythematous plaques involving the scalp, knees, extensor surface of elbows, neck, and back.
    • Plaques are raised, with a thick silvery scale covering the surface.
    • Psoriasis can also involve nails and joints, leading to psoriatic arthritis.
    • Nail involvement presents as pitting over the nail plates.
    • Arthritis can present with early morning stiffness which is relieved by physical activity.
    • Some drugs can worsen psoriasis (b-blocker, Li, ACEI, NSAIDs, and antimalarials).
    • Dx is a clinical one.
    • Histology shows epidermal hyperplasia or hyperproliferation with neutrophilic infiltration in the stratum corneum and thinned to the absent layer of the epidermis.
  • Worsening of psoriasis by certain drugs:
    • As a general rule, all drug-induced skin rashes should be
      managed by d/c the drug.
  • Rx of psoriasis:
    • depends on the severity of the disease.
    • Mild localized skin disease is Rx with topical steroids (betamethasone) or emollients or coal tar products (anthralin or calcipotriene).
    • For extensive/widespread disease, Rx includes methotrexate, cyclosporine, UV radiation, or immunomodulators.
    • Methotrexate is the initial DOC for pt with psoriasis and arthritis.
  • Tinea Versicolor:
    • fungal infection of the skin caused by Malassezia furfur.
    • Presents with multiple small circular maculae which varies in color (white, pink, brown).
    • Rash is more prominent in the summertime.
    • Generally, the lesions are the only symptom.
    • Rx with terbinafine antifungals.
    • Alternatively, any of the azoles can also be used.
  • Onychomycosis:
    • fungal infection of toenails or fingernails.
    • MCC is Trichophyton rubrum.
    • Nail dystrophies from other diseases can mimic this (psoriasis, lichen planus).
    • You can confirm dx with KOH exam of the nail scrapings.
    • The KOH exam will show dermatophytes hyphae and arthrospores.
    • Terbinafine is the TOC.
    • An alternative is an itraconazole.
  • Rosacea:
    • chronic acneiform condition characterized by vascular dilation in the central face.
    • Presents in adults 30-60.
    • There are exacerbations and remissions.
    • Symptoms include facial erythema, telangiectasias, and papules/pustules.
    • Looks a lot like acne, but no comedones are present.
    • Rx with topical metronidazole.
    • Pt with rosacea often have ocular symptoms.
    • Chalazion is a common one (it’s a cyst in the eyelid). Other eye complications include foreign body sensation and conjunctivitis.
  • Alopecia Areata:
    • Discrete, smooth, and circular areas of hair loss over the scalp with no scaling.
    • Usually develops over a few weeks and has a recurring pattern.
    • There is usually regrowth of hair in the involved areas over time. There is no associated scaling, scarring, or inflammation.
    • Rx is with topical or intralesional steroids.
    • Even after Rx, there is still a chance of recurrence, although it does speed up hair growth.
  • Tinea capitis:
    • Can present with a patch of hair loss on the scalp.
    • The lesion is well-demarcated, scaling, and somewhat erythematous.
    • Dx is usually with KOH exam of the hair stubs.
    • Microsporum Canis is a cause, which will have a bright green fluorescence when a lesion is observed under Wood’s UV lamp.
  • Keloid:
    • benign fibrous growth that develops in scar tissue.
    • These lesions can be painful and disfiguring.
    • Rx with intralesional steroids.
    • Look for hx of trauma (ex earring piercings)
  • Actinic Keratosis:
    • Presents as a slowly growing reddish-brown skin lesion.
    • It’s pre-malignant, with the potential to become squamous cell cancer of the skin.
  • Tetracycline:
    • often used for Rx of acne.
    • Doxycycline is a phototoxic agent and makes ppl more susceptible to sunburn.
    • On a side note, doxy can also cause esophageal ulceration if you don’t drink it with enough liquid.
    • Rx for sunburn includes replacement of lost fluids and relief for pain/pruritis with NSAIDs.
    • Diphenhydramine can be used for the itching.
  • Isotretinoin (systemic retinoid):
    • can cause hypertriglyceridemia in up to 25% of pt.
    • Thus, there is a risk of acute pancreatitis.
    • Look for the kid who is getting isotretinoin for acne Rx who develops pancreatitis.
    • If a pt develops triglyceridemia > 800, should d/c the drug.
  • Topical Retinoid:
    • teratogenic.
    • Topical retinoids aren’t associated with systemic side effects (hyperTG or hepatotoxic).
  • Herpes Zoster:
    • d/t reactivation of latent VZV infection earlier In life.
    • Any kind of stress on the body (fracture, infection, surgery) can reactivate the latent infection.
    • Presents with grouped vesicles in a specific dermatome, usually unilateral.
    • Pain is another prominent feature.
    • Rx with acyclovir.
    • Localized zoster lesions are transmitted only via direct contact with open lesions.
    • Contact precautions aren’t necessary for the community setting.
    • In the hospital, however, should put the pt in contact isolation until all the lesions have crusted.
    • As age increases, there is a higher chance that a recurrence will happen.
  • Postherpetic neuralgia (PHN):
    • Defined as persistence of pain or other symptoms for > 1 month after the resolution of skin lesions of herpes zoster.
    • It’s described as a burning sensation in the involved dermatome.
    • Agents proven to be effective for the pain include TCA, topical capsaicin cream, gabapentin, and long-acting oxycodone.
  • Photoaging:
    • arises from aging and UV light damage.
    • Intrinsic aging tends to cause fine wrinkles on an otherwise smooth skin surface.
    • If there is photodamage, it can result in coarse, deep wrinkles on a rough skin surface.
    • Photoaged skin is often marked with actinic keratoses, telangiectasias, and brown spots.
    • Cigarette smoke can have a significant impact on the skin (more wrinkles, especially at lateral corners of eyes).
    • Rx with tretinoin.
    • It helps reduce fine wrinkles, mottled hyperpigmentation, and roughness of the face.
    • It can also reduce actinic keratoses.
  • Erythrasma:
    • infection of the skin that occurs most often in intertriginous spaces and is d/t C. minutissimum.
    • Use of wood lamp shows coral-red fluorescence caused by Corynebacterium porphyries.
  • Pityriasis rosea:
    • self-limited condition manifests first as a single primary plaque (herald patch).
    • A generalized eruption develops 1-2 weeks later, with fine, scaling papules and plaques in a Christmas tree distribution.
  • Poison Ivy dermatitis:
    • presents with pruritic dermatitis composed of papules and vesicles which are distributed in a linear fashion.
    • Multiple lesions can be present in various areas around the body since touching other parts of the body will transfer the poison ivy resin.
    • More serious reactions can evolve into vesicles which can exude a serous fluid.
  • Tinea pedis:
    • MC dermatophyte infection.
    • Usually accompanied by involvement in another area (hands, neck, nails, or groin).
    • Presents as a slowly progressive, pruritic, erythematous lesion, usually btw the toes and extending to the sole and side of the foot.
    • There is a sharp border btw the involved and uninvolved skin.
    • Self limiting, but recurrent.
    • Rx with an antifungal cream.
  • Seborrheic Dermatitis (dandruff):
    • Pink-red erythema and scaliness in the scalp, face, and sometimes upper trunk.
    • Pruritis is usually mild.
    • Rx with selenium shampoo.
    • Sometimes it’s the first presenting sign of HIV infection.
  • Lichen Planus:
    • generally presents in middle age.
    • Involves skin, nails, mucous membranes of the mouth, and external genitalia.
    • Lesions are shiny, discrete, intensely pruritic, polygonal-shaped violaceous plaques and papules that are present on the flexural surfaces of the extremities.
    • Wrists are commonly involved.
    • A characteristic whitish lacy pattern is often seen on the surfaces of the papules and plaques.
    • Mucous membranes of the mouth and external genitalia can also be involved.
    • Dx is clinical.
    • Histology can show hyperkeratotic epidermis with irregular acanthosis and focal thickening in the granular layer of the epidermis.
    • Lichen planus is seen in association with liver disease, especially advanced disease 2/2 hep C infection.
    • Consider screening for it with H and P if you see lichen planus.
  • Acne Rx:
    • Mild acne is Rx initially with a topical retinoid.
    • Moderate acne can be Rx with topical retinoid and benzoyl peroxide or topical antibiotic.
    • More severe acne is treated by adding a topical antibiotic or systemic abx.
    • Abx are used only in combination with the other stuff.
    • Very severe cases can be rx with oral isotretinoin is no response after 3-6 months with combo of abx, topical retinoid, and benzoyl
      peroxide.
  • Pressure Ulcer:
    • Stage 1 has nonblanchable erythema of intact skin.
    • Stage 2 has a partial thickness loss of the epidermis, dermis, or both.
    • Stage 3 is deeper, causing a full-thickness loss with damage that might involve underlying fascia.
    • Stage 4 is very deep, and can possibly extend into the bone, muscle.
    • Should cover the wound with dressing/saline moistened gauze.
    • Pt should be turned every 2 hours to prevent it.
  • Sporotrichosis:
    • fungal infection d/t sporothrix schenckii.
    • Usually seen in ppl who do outdoor activities.
    • Starts as a popular lesion over the site of inoculation.
    • Eventually, the lesion ulcerates and there is non-purulent drainage over the lesion.
    • Dx is clinical and with culture.
    • Itraconazole for 3-6 months is Rx.
  • Tattoo:
    • Laser removal of tattoos can be done, but they lead to scar marks and skin discoloration.
  • Porphyria cutanea tarda:
    • d/t deficiency of uroporphyrinogen decarboxylase.
    • Painless blisters and increased fragility of the skin are seen.
    • There can also be facial hypertrichosis and hyperpigmentation.
    • Dx is with elevated urinary uroporphyrins.
    • Phlebotomy or hydroxychloroquine can provide relief.
    • There is often an association with hep C, and if pt also has Hep C, can give interferon-alpha.