Welcome to NP Certification Q&A presented by Fitzgerald Health Education Associates. This podcast is for NP students studying to pass their NP certification exam. Getting to the correct test answers means breaking down the exam questions themselves. Leading NP expert Dr. Margaret Fitzgerald shares her knowledge and experience to help you dissect the anatomy ofa test question so you can better understand how to arrive at the correct test answer. So, if you're ready, let's jump right in. 

A 62-year-old woman with Type 2 diabetes presents after noticing, “A bug bite on my left lower leg,” stating, “I'm not sure what bit me.” During this time, the area has increased in size, and she reports discomfort in the region. Examination reveals a tender, warm, red, erythematous area with poorly demarcated borders about 15 centimeters in diameter at its widest point on the anterior lower leg. Bilateral calf circumferences are equal. The patient is without fever or additional complaint, with no additional contributory history.

This most likely represents:

A. Deep vein thrombus
B. Erythema migrans
C. Cellulitis.
D. Contact dermatitis.

The correct answer is C. Cellulitis.

Where should we start? Given that we are asked what abnormality on the history and physical exam represents, this is a diagnosis question. As we've done with all the other Q&A podcasts, we need to take a look first into some background information. What is cellulitis? It's an acute infection of the subcutaneous tissue and skin, most often noted in the extremities. This infection follows some kind of an interruption in the skin's integrity, such as a wound, insect bite, abrasion, or other injury. Significantly less common, particularly in the outpatient setting, is cellulitis at a surgical or an IV site. Cellulitis is most often seen in the lower extremities, with the causative organism usually being a gram-positive organism such as group A beta-hemolytic strep, and much less commonly Staph aureus. And when it is Staph aureus, it's usually a strain that's methicillin-sensitive. And I know many of you come to the NP role from the acute care setting, and in the acute care setting, if it's Staph aureus, it's almost always MRSA, but this is usually methicillin-sensitive Staph aureus. Cellulitis typically presents as a poorly demarcated, warm erythematous area with associated edema, tenderness to palpation, and almost always unilateral. Diagnosis is made clinically based on history and physical exam, and diagnostic testing is usually not required. On rare occasions, cellulitis can result in systemic symptoms such as fever, malaise, chills and pain disproportionate for physical exam findings. Under those circumstances, certainly additional diagnostic testing should be considered. Cellulitis is actually a relatively common problem in primary care and can be managed as an outpatient with an oral antimicrobial. Now let's take a look at the question and the answer options.

To recap, a 62-year-old woman with Type 2 diabetes presents two days after noticing, “a bug bite” on her left lower leg,” stating, “I'm not sure what bit me.” During that time, the area has increased in size, and she reports discomfort in the region. Examination reveals a tender, warm, red, erythematous area with poorly demarcated borders about 15 centimeters at the widest diameter on the anterior lower leg. Calf circumferences is equal bilaterally. The patient is without fever or additional complaint with no additional contributory history.

This most likely represents:

Deep vein thrombus. This is incorrect. Acute deep vein thrombophlebitis, or deep vein thrombus, often abbreviated DVT, usually involves the veins of the lower extremity and pelvis. DVT risk factors, include local trauma to the leg, and the fact that she had a little bit of the bug bite doesn't qualify. Prolonged travel or rest, presence of varicose veins, a history of prior episodes of DVT, recent surgery, the use of estrogen containing hormonal contraception or postmenopausal hormonal therapy, and the immediate postpartum period within the first six weeks post-birth. None of these are mentioned in this question. If they are not mentioned, then they're not germane to the question. DVT almost always presents with diffuse leg swelling that is unilateral. And what are we told with this patient? Her leg circumferences are equal bilaterally. The other part, we're told with this woman that the findings are limited to the anterior lower leg. In other words, a front of the calf. And usually with DVT, it would be more around the entire circumference of the leg, with some more severe findings towards the back of the calf. But the big point here is we're told her leg circumferences are equal bilaterally. And that really does help rule out DVT. That along with the lack of the risk factors.

B. Erythema migrans. Now, this is tempting because it shows us she was bitten by a bug and erythema migrans is caused by a tick bite. But this is also incorrect. And that the report of the lesion here is not consistent with the description of erythema migrans, which is noted in stage one Lyme disease. The EM lesion as erythema migrans is often abbreviated, EM, the EM lesion usually has a bullseye or annular appearance with central clearing that evolves 3 to 30 days post tick bite. So, one thing to keep in mind. Yeah, she was just a few days ago. Yes, people can have the erythema migrans lesion as soon as three days after the tick bite, but usually it is more days out. Also, usually the EM lesion is also accompanied by body and joint aches as well as headache. The lesion is rarely itchy or painful and lesions can also occur away from the original bite site. So, you get it is a very fine point in this question on differential diagnosis. And that's the whole purpose of this exercise.
Option C. Cellulitis. Well, we now know this is the correct answer. She has two risk factors for this condition: Type 2 diabetes, and more importantly, a recent history of skin injury and this case, the insect bite has disrupted the skin's normal protective barrier, allowing for infection of the skin and subcutaneous tissue. Cellulitis is most often noted in a single lower extremity and most often below the knee. This condition is usually treated with an appropriate antimicrobial that has significant gram-positive activity. And I might bring a question like this back for future podcast with intervention. But remember, the antimicrobial can be as simple as oral cefalexin. It does a really, really nice job of covering both the Staph that produces beta lactamase, which is what Methicillin sensitive Staph aureus is, and excellent activity against the Streptococcus species.
Option D. Contact dermatitis. Obviously, that is not correct, and contact derm is usually associated with itchy lesions in the formation of vesicles, bullae, or an oozing appearance occurring after exposure to a triggering agent. Given the history of an insect bite along with lesion description, not the correct answer.

Key takeaway: Cellulitis, and in particular cellulitis suitable for treatment in the outpatient setting, usually presents with localized findings, as is described in this scenario. This is in contrast with the inpatient who has cellulitis, who has more extensive clinical findings.

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