What is the differential diagnosis, workup, and management for a 90-year-old female with bilateral lower extremity swelling, redness, and itching, and a history of anemia, aortic valve stenosis, carotid artery disease, diastolic heart failure, hypertension, hypocholesterolemia, hypothyroidism, obesity, and chronic kidney disease stage four, presenting with leukocytosis, hyponatremia, hyperglycemia, impaired renal function, elevated C-reactive protein (CRP), and normal lactic acid levels, with a negative venous duplex scan for deep vein thrombosis (DVT)?

Differential Diagnosis

The patient presents with bilateral lower extremity swelling, redness, and itching, which can be caused by a variety of conditions. Given the patient's complex medical history, it's essential to consider multiple possibilities.

• Single Most Likely Diagnosis
  • Cellulitis: The patient's symptoms of bilateral lower extremity swelling, redness, and itching, along with a elevated WBC count (11.9) and CRP (9.081), are consistent with cellulitis. The absence of DVT on venous duplex also supports this diagnosis.
• Other Likely Diagnoses
  • Chronic Venous Insufficiency: The patient's symptoms of lower extremity swelling and redness could be related to chronic venous insufficiency, especially given her history of ambulation with a walker and obesity.
  • Stasis Dermatitis: This condition is characterized by skin inflammation and irritation due to poor circulation, which could be contributing to the patient's symptoms.
  • Contact Dermatitis: The patient's itching and redness could be caused by an allergic reaction or irritation from a substance in contact with her skin.
• Do Not Miss Diagnoses
  • Necrotizing Fasciitis: Although less likely, this condition is a medical emergency that requires prompt attention. The patient's severe pain, elevated WBC count, and CRP level warrant consideration of this diagnosis.
  • Gas Gangrene: This rare but deadly condition can cause severe pain, swelling, and redness, and should be considered in the differential diagnosis.
• Rare Diagnoses
  • Erythema Ab Igne: A rare condition caused by prolonged heat exposure, which could be contributing to the patient's symptoms.
  • Lymphedema: Although less likely, lymphedema could be causing the patient's lower extremity swelling, especially given her history of obesity and chronic kidney disease.

Workup and Management

The patient's workup should include:

• Complete blood count (CBC) with differential to evaluate for signs of infection or inflammation
• Blood cultures to rule out bacteremia
• Wound culture or biopsy to identify the causative organism and guide antibiotic therapy
• Imaging studies, such as MRI or CT scan, to evaluate for underlying conditions like abscesses or necrotizing fasciitis
• Consideration of non-contrast MRI or alternative imaging modalities to minimize the risk of contrast-induced nephropathy (CIN) in patients with chronic kidney disease

CT Scan with IV Contrast

Given the patient's chronic kidney disease stage four, it's essential to weigh the benefits and risks of administering IV contrast. While a CT scan with IV contrast can provide valuable information, the risk of CIN is significant. Alternative imaging modalities, such as non-contrast MRI or ultrasound, should be considered to minimize the risk of CIN.

MRI without Contrast

MRI without contrast is a viable option for evaluating the patient's lower extremities, especially if there is concern about CIN. However, the sensitivity and specificity of non-contrast MRI may be lower than contrast-enhanced MRI, and the results should be interpreted with caution.