DDx: Common Dermatologic Disorders Flashcards Preview

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Flashcards in DDx: Common Dermatologic Disorders Deck (55)
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Ddx: Skin Infections (Bacterial)









A rapidly spreading deep subcutaneous dermis-based infection most often caused by S. aureus or group A streptococci.

Hx: Risk factors for lower extremity cellulitis include eczema, tinea pedis, onychomycosis, skin trauma (including insect bites, drug injection), chronic leg ulcers, long-standing diabetes mellitus, and edema. Risk factors for MRSA infection include recent close contact with persons having a similar infection, recent antibiotic use, recent hospitalization, hemodialysis, injection drug use, diabetes, and previous MRSA colonization or infection. 

Px: Characterized by a well-demarcated area of warmth, swelling, tenderness, and erythema. possibly accompanied by lymphatic streaking or fever and chills. 

Tx: Cellulitis without Purulence: Probable β-hemolytic streptococci or MSSA; MRSA unlikely.  

Oral : Dicloxacillin, Cephalexin, Clindamycin

Intravenous: Oxacillin, Nafcillin, Cefazolin, Clindamycin

Cellulitis with Purulence: Probable MRSA; risk factors for MRSAc; failure to respond to non-MRSA therapy:

Oral: Trimethoprim–sulfamethoxazole, Clindamycin, Doxycycline, Minocycline, Linezolid

Intravenous: Vancomycin, Linezolid, Daptomycin

$ Cephalexin

$ Dicloxacillin

$ Doxycycline

$ Trimethoprim–sulfamethoxazole

$$ Clindamycin

$$ Minocycline

$$$ Linezolid



A superficial skin infection involving the upper dermis and superficial lymphatics.

Px: It is usually erythematous in appearance (“St. Anthony's fire”) with well-demarcated borders and is almost always caused by group A streptococci.

Tx: Treatment is usually a β-lactam antibiotic (eg, penicillin or amoxicillin).



A pustular skin infection in the hair follicle. Causes include S. aureus and, less frequently, group A streptococci. 

Px: Typically affects the beard, pubic area, axillae, and thighs.

Tx: Folliculitis often is effectively treated with local application of heat and a topical antibiotic (mupirocin, chlorhexidine cleanser).

“Hot tub folliculitis” infection is generally caused by Pseudomonas aeruginosa
or Pseudomonas cepacia. The condition is usually self-limited, and therefore reassurance is all that is necessary. Antibiotic therapy is only indicated in recalcitrant
cases, or if patients are symptomatic.


Furuncles (boils/skin abscess) 

Tender, pus-containing nodules that commonly appear on the neck or in the axillae or groin but may occur at any skin site

Boil: infection of the hair follicle that extends into the dermis and subcutaneous tissues

Abscess: Pus collections in the dermis and deeper tissues 

Hx: Nearly always are caused by S. aureus. 

Dx: Cultures from purulent material can distinguish MRSA from methicillin-susceptible S. aureus (MSSA) and can guide treatment.

Tx: Warm compresses to facilitate drainage may be adequate therapy for small furuncles. Incision and drainage (I & D) is required for larger furuncles and all abscesses.  Incision and drainage may be adequate therapy for skin abscesses, and systemic antibiotics are not routinely required.  However, they may be indicated if the patient is febrile or immunocompromised, has diabetes, or is at risk for MRSA or if there is a surrounding cellulitis




A superficial infection of the skin (epidermis) characterized by a group of yellowish, crusted pustules.  caused by staphylococci (staph aureus) or streptococci.

Hx: Predisposing factors include poor hygiene, neglected minor trauma, and eczema.

Tx: Limited disease usually can be treated effectively with topical mupirocin or bacitracin; more extensive disease can be treated with a cephalosporin, penicillinase-resistant penicillin, or β-lactam-β-lactamase inhibitor.



An ulcerative form of impetigo usually caused by streptococci or staphylococci.

Px: The classic findings are superficial, saucer-shaped ulcers with overlying crusts, typically on the legs or feet.

Tx: Effective treatment consists of cleansing with an antibacterial wash followed by topical mupirocin plus oral cephalexin, dicloxacillin, or clindamycin. If MRSA is suspected or there is β-lactam allergy, one should consider other options.



Ecthymia Gangrenosum

Ecthyma gangrenosum is an ulcerative infection involving the dermis usually caused by Pseudomonas aeruginosa.

Hx: It is usually seen in immunocompromised patients and may indicate pseudomonal sepsis. 

Px: Classic findings are ulcers with a central gray-black eschar and erythematous halo, typically on the legs or feet.

Tx: Initial therapy usually involves an antipseudomonal penicillin plus an aminoglycoside.




Tinea capitis

Caused by T. tonaurans

Tx: Systemic therapy is necessary for a cure,

Griseofulvin is considered the treatment of choice in the United States, and should be used for 4 to 8 weeks.

Terbinafine, itraconazole, fluconazole, and ketoconazole can also be used. If fluconazole were to be used, the treatment duration would only be for 3 to 4 weeks.

Topical ketoconazole shampoo or selenium sulfide lotion may kill spores on the hair.



Tinea corporis (“ringworm”)

Scaly patch with central clearing and an active border of erythema, papules, and vesicles. Tinea is more erythematous than BCC and usually has a larger area of central clearing.

Most commonly caused by Trichophyton rubrum



Tinea cruris

Caused by T mentagrophytes

Occurs in the groin


Ddx: Common rashes

Erythema multiforme (EM)



The true cause is multifactorial, but familial factors are involved. The key factors are follicular keratinization, angrogens, and Propionibacterium acnes. In acne, the kertatinization pattern in the pilosebaceous unit changes, and keratin becomes more dense, blocking the secretion of sebum. The keratin plugs are called “comedones.”

Hx: Contributory factors to acne include certain medications, emotional stress, and occlusion and pressure on the skin, such as by leaning the face on the hands (acne mechanica).

Acne is not caused by dirt, chocolate, greasy foods or the presence or absence of any foods in the diet.

Tx: Initial management of comedonal acne without a significant inflammatory component includes:

Topical retinoids with the addition of 

Organic acid preparations (eg, salicylic, azelaic, or glycolic acid) if initial therapy fails.  

Benzoyl peroxide, a widely used antibacterial agent, is another option for patients with comedonal acne, although it is preferred for inflammatory acne.  Some patients with comedonal acne will develop inflammatory features, and benzoyl peroxide can be added at that time.

Topical antibiotics (eg, erythromycin, clindamycin) is used in most patients with moderate or moderate-to-severe inflammatory acne require . 

Oral isotretinoin is indicated for nodular acne, severe acne, or moderate recalcitrant acne. 🕷

Oral antibiotics (eg, tetracyclines) are reserved for patients with severe or nodular acne and for moderate inflammatory acne unresponsive to topical antibiotics.  Oral antibiotics are also considered in patients with widespread inflammatory acne (eg, back, upper arms) that makes topical therapy impractical.

In addition, since both tetracycline and isotretinoin cause pseudotumor cerebri, the two medications should never be used together.


Acute urticaria (hives)



An H1-blocking nonsedating antihistamine (e.g., cetirizine [Zyrtec]), which will stop the likely allergic cause of her urticaria.

A short course of systemic glucocorticoids may also be helpful for patients with widespread or highly symptomatic involvement. In persistent cases, an H2-blocking antihistamine is sometimes added, although the effectiveness of doing so has not been established.

Topical corticosteroids can occasionally provide additional relief for symptomatic urticarial lesions

❗Concerning features:  wheezing; stridor; and lip, tongue, or eyelid swelling; dyspnea, difficulty clearing secretions, or hemodynamic instability

Tx: Administration of epinephrine would be indicated.


Atopic Dermatitis (eczema)

The rash may look like rough, red plaques with some flaking that can affect the face, neck, upper trunk, and behind the knees. The flexural surfaces are often involved. Pruritus may be severe.

Most patients have the onset of eczema in childhood, and onset after the age of 30 is very


Basal cell carcinomas (BCCs)

Basal cell carcinomas (BCCs) most commonly appear as pearly telangiectatic papules. because the most important risk factors for the development of BCCs are fair skin and sun exposure (the same risk factors as for AKs), the two often occur in the same area.



Dermatofibromas are firm, dermal nodules approximately 6 mm in diameter; the surface often is hyperpigmented (Plate 29 :). Dermatofibromas are most commonly seen on the legs of women but also occur on the trunk in both men and women. Excision is indicated only if the lesion is symptomatic, has changed, or bleeds.


Erythema multiforme (EM)

erythema multiforme (EM), which is an acute, often recurrent mucocutaneous eruption that usually follows an acute infection, most frequently recurrent herpes simplex virus (HSV) infection. It may also be idiopathic or drug related. Most patients are between 20 and 40 years of age. Lesions range in size from several millimeters to several centimeters and consist of erythematous plaques with concentric rings of color. The dusky center may become necrotic and can form a discrete blister or eschar. Few to hundreds of lesions develop within several days and are most commonly located on the extensor surfaces of the extremities, particularly the hands and feet. Lesions occur less frequently on the face, trunk, and thighs. Mucosal lesions are present in up to 70% of patients and involve the cutaneous and mucosal lips, gingival sulcus, and the sides of the tongue. Mucosal lesions consist of painful erosions or, less commonly, intact bullae. The conjunctival, nasal, and genital mucosal surfaces can also be affected. Patients may have low-grade fever during an EM outbreak. Lesions usually last 1 to 2 weeks before healing; however, hyperpigmentation may persist. Recurrences are common, particularly in HSV-associated infection. Treatment of EM is primarily symptomatic. Systemic corticosteroids may provide symptomatic improvement but may be associated with complications. Antiviral therapy does not shorten the EM outbreak in HSV-associated infection, but continuous prophylactic antiviral therapy may help prevent further episodes. Treatment for bacterial infection-associated EM is appropriate for management of the specific active infection; however, there are no studies that demonstrate that treatment impacts the duration of the EM lesions. Antibiotic therapy is based on identification of an infectious cause. If EM is thought to be due to a new drug, the drug should be discontinued.


Epidermoid inclusion cyst

The most common type of skin cyst is an epidermoid inclusion cyst. Usually present on the face, neck, or chest, this type of cyst is made up of epidermal cells that are present in the dermis. Patients usually note a nontender lump that may become painful if infected. In this case, treatment involves incision and drainage and removal of the cyst and cyst wall.


Herpes zoster ophthalmicus (shingles)

Ophthalmic zoster, if not treated promptly, can lead to blindness. Shingles, which is reactivation of varicella-zoster virus, can occur any time after the primary varicella infection. It often begins with a prodrome of intense pain, and in more than 90% of patients, it is associated with pruritus, tingling, tenderness, or hyperesthesia. The cutaneous eruption typically involves a single dermatome and rarely crosses the midline. In a recent, prospective multicenter study, eye redness and rash in the supratrochlear nerve distribution had a statistically significant association with clinically relevant eye disease. One hundred percent of patients who developed moderate to severe eye disease presented with a red eye. Hutchinson sign (zoster eruption on the tip of the nose) was not predictive of clinically relevant eye disease. Clinical diagnosis is based on both history and physical examination. Testing by direct fluorescent-antibody testing or by polymerase chain reaction can confirm the diagnosis; however, decisions regarding antiviral therapy are often based on the history and physical examination rather than reliance on laboratory testing.



red, volcano-like nodules with a prominent central keratin plug. They are considered to be a subtype of well-differentiated squamous cell carcinoma. They grow rapidly and may reach a size of several centimeters within a few weeks. Classic keratoacanthomas eventually stabilize in size and may spontaneously regress without treatment.



A lipoma is a group of fat cells encased in a thin fibrous capsule. These are typically softer and more pliable than cysts and can be single or multiple. Lipomas can be superficial or deep and usually do not need to be removed. However, if there is growth or pain, removal should be carried out.


Nummular eczema

Round, well-demarcated, eczematous patches (1-10 cm) found on the extremities and trunk. Pruritus may be intense, which results in scratching. The scratch marks may be the best way to discriminate nummular eczema from superficial BCC. Onset is usually spontaneous with no inciting event.


Peripheral Edema

Bilateral edema:

CHF (dyspnea, rales, or JVD) would necessitate a chest x-ray to rule in the diagnosis, followed by an echocardiogram.

Liver Failure: Ascities; Dx: Liver function studies are needed. If these are absent, the clinician should check an urinalysis. If the sediment is abnormal, nephritic syndrome or acute tubular necrosis (ATN) is the likely diagnosis.

Medications:  Antihypertensives (ACE), such as calcium channel blockers are well known to cause this, but direct vasodilators, β-blockers, centrally acting agents, and antisympathetics also can cause edema. Of the diabetic medications, insulin sensitizers, such as rosiglitazone often cause edema. Hormones, corticosteroids, and NSAIDs also cause problems.

Unilateral Edema:



Dx: C4 level and C1 esterase



Chronic spontaneous Hx:


Pityriasis rosea

A self-limited papulosquamous eruption. The classic history includes a single herald patch (an oval, slightly raised plaque with scale) followed in the next 1 to 2 weeks with a more generalized eruption. It will spontaneously resolve in 6 to
12 weeks, and recurrences are uncommon. The treatment is symptomatic, and includes antihistamines or corticosteroids to relieve itch.


Pyoderma gangrenosum

Pyoderma gangrenosum is an ulcerative skin condition typically associated with an underlying systemic condition, such as inflammatory bowel disease, rheumatoid arthritis, spondyloarthritis, or a hematologic disease or malignancy (most commonly acute myelogenous leukemia). Lesions often are multiple and tend to appear on the lower extremities. They begin as tender papules, pustules, or vesicles that spontaneously ulcerate and progress to painful ulcers with a purulent base and undermined, ragged, violaceous borders. 



A chronic skin condition in young adults. In the early phase, the sharply demarcated erythematous plaques with slight scale may resemble superficial BCC.

As the psoriatic area matures, a silvery-white scale develops that has characteristic pinpoint bleeding when removed,

Plaques are symmetrically distributed and usually occur on scalp, extensor surfaces (elbows, knees and back).

Tx: For localized skin rashes, topical corticosteroids are appropriate therapeutic agent. Topical pimecrolimus is effective for inverse psoriasis (located on the perianal and genital regions) or on the face and ear canals, but is generally not used for lesions on the
trunk or extremities.



In stage I, there is persistent erythema, generally with telangiectasia formation. Stage II is characterized by the addition of papules and tiny pustules. In stage III, the erythema is deep and persistent, the telangiectases are dense, and there may be a solid appearing edema of the central part of the face due to sebaceous hyperplasia and lymphedema (rhinophyma and metophyma).

Tx: Management may include topical or oral therapies. Topical metronidazole, clindamyacin, and sodium sulfacetamide can work, but oral antibiotics are more effective than topical treatments.

Minocycline or doxycycline are very effective first-line therapies.

Topical steroids are NOT generally effective.


Seborrheic keratoses

Seborrheic keratoses are common benign, painless neoplasms that present as brown to black, well-demarcated papules with a waxy surface and a “stuck-on” appearance (Plate 28 :). Seborrheic keratoses are more common in older patients. Treatment is not indicated unless the growths are inflamed, irritated, or pruritic.