Dermatology Notes for the USMLE Step 3
Also in PDF format attached below
Dermatology Notes for the USMLE Step 3
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 diagnosis and stage the lesion. Eventually, if it is melanoma, youíll want to do a complete excision, which is curative a lo 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 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: inflammatory skin disorder characterized by hyperproliferation and abnormal differentiation of the epidermis. There are sharply demarcared 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. The arthritis can present with early morning stiffness which is relieved by physical activity. Some drugs can worsen psoriasis (b-blocker, Li, ACEI, NSAIDs, and anti-malarials). Dx is a clinical one. Histology shows epidermal hyperplasia or hyperproliferation with neutrophilic infiltration in the stratum corneum and thiined to 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 severity of 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 include methotrexate, cyclosporine, UV radiation, or immunomodulators. Methotrexate is the initial DOC for pt with psoriasis and arthritis.
Tinea Versicolor: fungal infection of skin caused by Malassezia furfur. Presents with multiple small circular macula which vary in color (white, pink, brronw). Rash is more prominent in summertime. Generally the lesionsare the only symptom. Rx with terbinafine anti fungals. Alternatively, any of the azoles can also be used.
Onychomycosis: fungal infection of toenails or finger nails. 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 dermatophytic hyphae and arthrospores. Terbinafine is the TOC. An alternative is 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 comedoens are present. Rx with topical metronidazole. Pt with rosacea often have ocular symptoms. Chalazion is a common one (itís 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 scalin, 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 lesion isobserved under Woodís UV lamp.
Keloid: benign fibrous growth that develops in scar tissue. These lesions can be painful and fdisfiguring. Rx with intralesional steroids. Look for hx of traum a(ex earring piercings)
Actinic Keratosis: Presents as slowly growing reddish brown skin lesion. Itís pre-malignant, with potential to become squamous cell cancer of the skin.
Tetracycline: often used for Rx of acne. Doxycycline is a phototoxic agent and make ppl more susceptible to sunburn. On a side note, doxy can also cause esophageal ulceration if you donít 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 isotretionoin for acne Rx who develops pancreatitis. If a pt develops triglyceridemia > 800, should d/c the drug.
Topical Retinoid: teratogenic. Topical retinoids arenít associated systemic side effects (hyperTG or hepatotoxic).
Herpes Zoster: d/t reactivation of latent VZV infectio 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 the open lesions. Contact prevautions arenít necessary in 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 resolution of skin lesions of herpes zoster. Itís 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 significant impact on skin (more wrinkles, especially at lateral corneres 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 skin that occurs most often in intertriginous spaces and is d/t C. minutissimum. Use of wood lamp shows coral red fluorescence cause 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 a pruritic dermatitis composed of papules and vescicles which are distributed in a linear fashion. Multiple lesions can be present in various areas around the bodhy, since touching other parts of body will transfer the poison ivy resin. More serious reactions can evolve into vescicles which can exude a serous fluid.
Tinea pedis: MC dermatophyte infection. Usually accompanied by involvement in another area (hands, necknails, 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 limting, but recurrent. Rx with 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 itís 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. Wristss 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 topical retinoid. Moderate acne can be Rx with topical retinoid and benzoyl peroxide or topical antibiotic. More severe acne is treated with 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 isotretinion is no response after 3-6 omnths 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 are deeper, causing a full thickness loss with damage which might involve underlying fascia. Stage 4 are very deep, and can possibly extend into the bone, muscle. Should cover wound with dressing/saline moistened gauze. Pt should be turned every 2 hours to prevent.
Sporotrichosis: funal 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 tehr eis 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 curanea tarda: d/t deficiency of oroporhyinogen decarboxylase. Painless blisters, and an icreased fragility of the skin are seen. There can also be facial hypertrichosis and hyperpifmentation. 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.
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