MKSAP quiz on dermatology
The following cases and commentary, which focus on distinguishing infectious from noninfectious causes of skin findings, are excerpted from ACP's Medical Knowledge Self-Assessment Program (MKSAP 17).
Case 1: New skin nodule
A 78-year-old woman is hospitalized for management of acute worsening of chronic kidney disease. On the third hospital day, she develops a painful nodule under the tape adjacent to the site of a peripheral intravenous catheter on her left forearm. Medical history is also significant for hypertension and type 2 diabetes mellitus. She currently takes amlodipine, insulin, and furosemide.
On physical examination, temperature is 38.3 °C (100.9 °F), blood pressure is 125/85 mm Hg, pulse rate is 70/min, and the respiration rate is 12/min. A tender, fluctuant, erythematous nodule with 2 cm of surrounding erythema is present on the left forearm. There is no lymphadenopathy. The remainder of the physical examination is noncontributory.
The leukocyte count is 13,000/μL (13 × 109/L). The nodule is incised and drained. Microscopic examination shows numerous leukocytes and small gram-positive cocci; culture results are pending.
Q: Which of the following is the most appropriate antibiotic therapy for this patient?
Case 2: Red, swollen legs
A 53-year-old woman is evaluated in the emergency department for a 1-week history of increased swelling, redness, and pain in her lower legs. She has not had trauma to her legs and has not noted any drainage. She has not had fevers and has otherwise felt well. Medical history is significant for heart failure. Medications are ramipril, metoprolol, and furosemide, which she has not been taking recently as she has not had her prescriptions refilled.
Figure 1. Copyright American College of Physicians
On physical examination, vital signs are normal. The neck veins are prominent. Mild bibasilar crackles are present. There is no inguinal lymphadenopathy, and the remainder of the general examination is unremarkable. Skin findings are shown. Figure 1
Q: Which of the following is the most likely diagnosis?
B. Contact dermatitis
C. Deep venous thrombosis
D. Stasis dermatitis
Case 3: History of MRSA infections
A 25-year-old man is admitted to the hospital for chills and fever of 3 days' duration. He reports that he injects heroin daily. Medical history is notable for multiple methicillin-resistant Staphylococcus aureus–associated skin and soft tissue infections and for vancomycin hypersensitivity, which causes respiratory failure and hypotension. He takes no medications.
On physical examination, temperature is 39.4 °C (102.9 °F), blood pressure is 104/65 mm Hg, pulse rate is 110/min, and respiration rate is 20/min. A recent injection site in the antecubital fossa is noted, with erythema, tenderness to palpation, and warmth. He has no mucosal lesions or lymphadenopathy. Cardiopulmonary examination is normal. The remainder of the examination is normal.
Laboratory studies show a leukocyte count of 19,000/µL (19 × 109/L) with 95% neutrophils.
Multiple blood cultures reveal gram-positive cocci in clusters. Findings on chest imaging and electrocardiography are normal.
Q: Which of the following is the most appropriate empiric antibiotic treatment for this patient?
Case 4: Eye swollen shut
A 20-year-old woman is evaluated for a 3-day history of pain, swelling, and redness of the right eye. She cannot open her eye because of the swelling. One week ago, she developed a fever with sinus congestion and postnasal drainage. Except for a continued subjective fever, these symptoms have resolved. She has no history of eye trauma or surgery. She takes no medications.
On physical examination, temperature is 38.0 °C (100.4 °F), blood pressure is 100/62 mm Hg, and pulse rate is 88/min. BMI is 23. Examination of the right eye shows red and edematous upper and lower lids with conjunctival erythema. Pupillary reflex to light is intact. Inspection reveals no foreign bodies. She is unable to move her eye. A limited funduscopic examination is normal. The left eye is normal, and the remainder of the physical examination is unremarkable.
Q: Which of the following is the most likely diagnosis?
C. Orbital cellulitis
D. Preseptal cellulitis
Case 5: Vesicles on a postop patient
A 62-year-old man was admitted to the ICU for high fevers associated with sepsis following hip replacement surgery. Since the procedure he has been relatively immobile except when receiving physical therapy. Two days after surgery, he developed fine superficial vesicles on the back. Except for pain following the procedure, he has felt well. Medical history is otherwise unremarkable, and his only medication is as-needed acetaminophen-oxycodone.
Figure 2. Copyright American College of Physicians
On physical examination, temperature is 37.9 °C (100.2 °F). The rest of his vital signs are normal. Skin findings are shown. Figure 2
The surgical site is clean and dry. The remainder of the examination is unremarkable.
Q: Which of the following is the most likely cause of this acute eruption?
A. Allergic contact dermatitis
. B. Candida albicans infection
C. Miliaria crystallina
. D. Staphylococcus aureus folliculitis
Case 6: Pedal edema
A 61-year-old woman with long-standing pedal edema is evaluated for redness on the bilateral lower legs. She notes that the edema worsens over the course of the day but is improved with elevation of her legs. She reports no pain or pruritus, no calf tenderness, no shortness of breath, no palpitations, and otherwise feels well. Medical history is significant for obesity but is otherwise unremarkable. She takes no medications.
Figure 3. Copyright American College of Physicians
On physical examination, vital signs are normal. BMI is 36. There is no jugular venous distention. The lungs are clear, and an S3 is not present. Pedal pulses are normal, and there is no calf tenderness. Skin findings are shown. Figure 3
The remainder of the physical examination is noncontributory.
Q: Which of the following is the most appropriate treatment?
A. Compression stockings
B. Oral cephalexin
C. Oral furosemide
D. Topical mupirocin
Answers and commentary
Correct answer: D. Vancomycin.
This patient should be treated with vancomycin. Hospital-acquired skin and soft-tissue infections should be treated as a methicillin-resistant Staphylococcus aureus (MRSA) infection until culture results are received and therapy can be tailored appropriately. Hospital-acquired skin infections are increasingly caused by MRSA, and coverage against this organism in the hospital setting is important to prevent further morbidity and mortality, particularly in high-risk patients. Once culture and sensitivity results are known, antibiotic therapy can be focused toward a specific organism. In the patient described here, a local abscess and surrounding cellulitis with corresponding fever and leukocytosis suggests the potential for systemic involvement.
Amoxicillin-clavulanate should not be used because these antibiotics do not provide coverage against MRSA organisms.
Similarly, cephalexin is often effective against multiple skin and soft-tissue infections and may be considered first-line therapy for an abscess and cellulitis in the ambulatory setting; however, it too is ineffective against MRSA.
Although meropenem is a potent antibiotic with broader antimicrobial coverage, it is not effective against MRSA infection and thus would not be an appropriate choice for this patient.
Several strategies may be used to attempt to reduce rates of MRSA infection in hospitalized patients. Routine screening and active surveillance cultures for MRSA colonization are obtained in some institutions to identify carriers and to guide use of contact precautions and possibly attempted decontamination with intranasal mupirocin. However, the efficacy of this practice is not clear except in the setting of an acute outbreak. Daily chlorhexidine bathing has been shown to decrease the risk of colonization and infection with drug-resistant and other organisms in ICU settings.
Correct answer: D. Stasis dermatitis.
This patient has stasis dermatitis. Stasis dermatitis, especially in the acute setting, can present with brightly erythematous, edematous plaques, as shown in the figure, that are tender to palpation and can be slightly warm to touch. Overlying scale and serum crust also can develop as a consequence of fluctuating edema (as seen in the figure). Differentiating stasis dermatitis from cellulitis can be difficult; however, the presence of similar-appearing erythematous plaques bilaterally in an afebrile patient with no lymphadenopathy or other symptoms or signs of infection would be unusual for cellulitis. Because stasis dermatitis usually results from decreased venous drainage or excess fluid in dependent areas causing increased vascular permeability and stretching of the skin, the clinical scenario of a patient with heart failure who has recently stopped taking a diuretic also is supportive of a diagnosis of stasis dermatitis. Chronic stasis dermatitis will cause more brown discoloration, suggesting a longer term process, but acute stasis dermatitis can present as bright red patches/plaques. Treatment typically includes optimization of volume status or external compression stockings to decrease fluid volume and skin stretching in dependent areas.
Cellulitis presents as a painful, erythematous, well-demarcated patch that is warm to touch. The presence of fever, lymphadenopathy, or other evidence of infection, such as an elevated leukocyte count, also would suggest this diagnosis. It is important to consider alternative diagnoses when there are erythematous patches on both legs.
Contact dermatitis may present with localized inflammation at the site of exposure to an irritant and may cause erythema and edema. However, it is often pruritic and may be accompanied by bullae and oozing. Contact dermatitis may also be preceded by a history of application of a sensitizing agent in the area.
Deep venous thrombosis can present as a swollen, erythematous leg. Although bilateral deep venous thromboses can occur, this is a less likely cause in this patient.
Correct answer: B. Daptomycin.
The most appropriate treatment for this patient is daptomycin. He has a history of methicillin-resistant Staphylococcus aureus (MRSA) skin infections and now presents with injection drug use–associated cellulitis and bacteremia with gram-positive cocci in clusters, presumably MRSA. Because of his history of vancomycin intolerance, daptomycin, an alternative to vancomycin for the empiric treatment of MRSA-associated bacteremia and infective endocarditis, should be given. Daptomycin is a lipopeptide-type antibiotic and is bactericidal against MRSA. He will require echocardiography and repeat blood cultures after intravenous antibiotics have been initiated. Additionally, patients receiving daptomycin should be assessed regularly for clinical or laboratory signs of muscle weakness or pain, particularly in those receiving statin-based lipid-lowering agents or with kidney disease. Intravenous antibiotics must be administered for at least 2 weeks for S. aureus bacteremia.
Ceftriaxone could be used to treat nonpurulent cellulitis because β-hemolytic streptococci are the likely cause. However, it does not provide effective coverage against MRSA.
Imipenem, a broad-spectrum β-lactam antibiotic with activity against many aerobic and anaerobic bacteria, does not provide effective coverage against MRSA.
Additionally, S. aureus that may be resistant to methicillin also may be resistant to oxacillin, nafcillin, and other β-lactam agents, including ceftriaxone and imipenem. Nafcillin or oxacillin would be appropriate choices if the infection were found to be caused by methicillin-susceptible S. aureus. Until that time, however, empiric therapy should reliably target MRSA. The only β-lactam with reliable activity against MRSA is ceftaroline, a fifth-generation cephalosporin approved by the FDA for treatment of skin infections and community-acquired bacterial pneumonia.
Correct answer: C. Orbital cellulitis.
This patient has orbital cellulitis, which is inflammation of the structures of the orbit, including the extraocular muscles and orbital fat. Orbital cellulitis often results from a contiguous dental or sinus infection, as was likely present in this patient. Clinical characteristics of orbital cellulitis include eyelid swelling, ophthalmoplegia, pain with eye movement, and occasionally proptosis. Because it is a deep infection and involves critical structures, rapid diagnosis and treatment are necessary to preserve vision and prevent extension to central nervous system structures. CT is used to evaluate the extent of infection and to exclude abscess, which may need surgical drainage. This patient requires hospitalization and intravenous antibiotics.
Blepharitis is inflammation of the sebaceous glands or lash follicles of the eyelid, which can progress to conjunctivitis or keratitis. It usually presents with findings limited to the eyelid, although patients may complain of a gritty, burning sensation in the eye. Blepharitis is not associated with the key findings of orbital cellulitis.
Endophthalmitis is inflammation of the aqueous and vitreous humors. Symptoms may include visual loss, photophobia, and ocular pain and discharge. It is usually caused by bacterial or fungal infection following surgery, especially for cataracts. Other causes are globe trauma and foreign bodies.
Preseptal cellulitis is inflammation that is limited to the areas of the eyelids and facial tissues that are anterior to the orbital septum. It is more common than orbital cellulitis in adults and can usually be differentiated from orbital cellulitis by pain localized to the anterior tissues without ophthalmoplegia, pain with eye movement, or proptosis, which this patient has. Therefore, it is a less likely diagnosis in this patient.
Correct answer: C. Miliaria crystallina.
This patient's rash is consistent with a diagnosis of miliaria crystallina. Miliaria, or “heat rash,” is characterized by the eruption of fine red papules and pustules specifically located on the back, typically after immobilization in the supine position. Miliaria is caused by superficial clogging of the eccrine sweat glands, which leads to the development of minute pustules that rupture easily and can be wiped off. The clogging may be partially due to overgrowth of Staphylococcus epidermidis. Treatment involves implementing measures to decrease sweating and topical measures such cool baths and the use of loose clothing.
Allergic contact dermatitis on the back would appear as an eczematous dermatitis with pruritus on the area exposed to the allergen. This patient does not have pruritus or clinical findings consistent with an allergic contact dermatitis.
Candida albicans infections occur in hot, moist occluded areas, such as the armpits, groin, and beneath the breasts. The rash is not usually diffuse and will typically have some desquamation at the edges. The papules cannot be wiped off as with miliaria crystallina.
Staphylococcal folliculitis will cause more deep-seated follicular pustules, and the area would be red, swollen, and painful. Although Staphylococcus aureus is responsible for a wide range of skin infections such as folliculitis, abscesses, furuncles, carbuncles, impetigo, cellulitis, ecthyma, staphylococcal scalded skin syndrome, and erysipelas, this patient's clinical presentation is not consistent with an infection with this organism.
Correct answer: A. Compression stockings.
This patient has stasis dermatitis, and compression stockings should be used. Stasis dermatitis is characterized by red, inflamed, pitted skin on the lower legs. It occurs in patients with venous stasis disease or other causes of chronic lower extremity edema. Decreased venous drainage causes an increase in extravascular tissue fluid that results in stretching of the skin and a subsequent propensity for loss of barrier integrity. Also, because the shins are often one of the driest parts of the body and are easily excoriated, dermatitis in this area is common. Compression stockings help to increase the venous return, decrease the stretching of the skin, and reduce the risk of ulceration.
Stasis dermatitis is frequently confused with cellulitis. The four cardinal signs of cellulitis are erythema, pain, warmth, and swelling; associated lymphadenopathy can occur. Systemic symptoms, including fever, chills, and malaise, also may be present. This patient does not have fever, pain, or clinical findings consistent with cellulitis, and it is unlikely for cellulitis to present on both legs simultaneously. Compared with cellulitis, the redness on the anterior shins in patients with stasis dermatitis is often bilateral and warm to the touch but typically is not tender. Therefore oral cephalexin is not indicated.
This patient has edema related to the venous stasis but has no jugular venous distension, no crackles, and no S3. Given the absence of volume overload, furosemide would not be indicated.
Topical mupirocin would be indicated for impetigo, but this patient has no bullae, crusts, or erosions that would be seen in impetigo.
The information included herein should never be used as a substitute for clinical judgment and does not represent an official position of ACP. More information on MKSAP is online.
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