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Step 1: Identify the Problem
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PATIENT 
Mrs. S is a 58-year-old woman who comes to an urgent care clinic complaining of painful swelling of her left calf that has lasted for 2 days. She feels slightly feverish but has no other symptoms such as chest pain, shortness of breath, or abdominal pain. She has been completely healthy except for hypertension, osteoarthritis of her knees, and a cholecystectomy, with no history of other medical problems, surgeries, or fractures. Her only medication is hydrochlorothiazide. She had a normal pelvic exam and Pap smear 1 month ago. Physical exam shows that the circumference of her left calf is 3.5 cm greater than her right calf, and there is 1+ pitting edema. The left calf is uniformly red and very tender, and there is slight tenderness along the popliteal vein and medial left thigh. There is a healing cut on her left foot. Her temperature is 37.7°C. The rest of her exam is normal.
What is Mrs. S’s problem list?
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Problem lists should begin with the acute problems, followed by chronic active problems, ending with inactive problems. Mrs. S’s problems are (1) painful left leg edema with erythema, (2) hypertension, (3) osteoarthritis of the knees, and (4) status post cholecystectomy.
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Step 2: Frame the Differential Diagnosis
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How do you frame the differential diagnosis for edema?
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As discussed in Chapter 17, Edema, the problem-specific organization of the full differential diagnosis starts with the distribution of the edema: generalized versus unilateral and limb versus localized. The causes of edema are fairly distinct for each of these subcategories. For instance, heart failure and chronic kidney disease cause generalized not unilateral edema.
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Step 3: Organize the Differential Diagnosis
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Since the edema differential is framed using the pivotal point of edema distribution, it is not necessary to organize it—step 3 has already been done.
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Step 4: Limit the Differential Diagnosis
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What are the pivotal points in Mrs. S’s presentation? How would you limit the differential?
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Mrs. S has acute unilateral leg edema, a pivotal point that leads to a limited portion of the edema differential.
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Diagnostic possibilities are now narrowed to a distinct subset of diseases that can be organized using an anatomic framework:
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Skin: Stasis dermatitis
Soft tissue: Cellulitis
Calf veins: Distal deep venous thrombosis (DVT)
Knee: Ruptured Baker cyst
Thigh veins: Proximal DVT
Pelvis: Mass causing lymphatic obstruction
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Step 5: Use History and Physical Exam Findings to Explore Possible Diagnoses
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Consider the risk factors for each of the diagnostic possibilities as well as their associated symptoms and signs. For example, venous insufficiency is a risk factor for stasis dermatitis, and there may be hemosiderin staining along the malleolar surface on physical ...