Differential Diagnosis

The patient's presentation suggests a complex condition with multiple possible causes. The following differential diagnosis is organized into categories to guide further evaluation and management.

• Single most likely diagnosis
  • Venous stasis ulcer with superimposed infection: The patient's history of fluid retention, significant swelling, and a flap-type wound on the dorsal aspect of the calf, along with increased redness and tenderness, are consistent with a venous stasis ulcer that may have become infected. The patient's age and mobility issues also increase the risk for this condition.
• Other Likely diagnoses
  • Cellulitis: The patient's symptoms of redness, swelling, and tenderness, particularly in the context of a recent trauma and a flap-type wound, could indicate cellulitis, a common bacterial skin infection.
  • Deep Vein Thrombosis (DVT): Although less likely given the patient's description of the wound and swelling pattern, DVT should be considered, especially in the context of recent trauma and immobilization.
  • Arterial Ulcer: Less likely due to the location and description of the wound, but possible if the patient has significant peripheral arterial disease.
• Do Not Miss (ddxs that may not be likely, but would be deadly if missed.)
  • Necrotizing Fasciitis: Although rare, this condition is a medical emergency that can arise from a skin infection, including after trauma. The patient's symptoms of significant swelling, redness, and tenderness, along with a history of a chill, warrant consideration of this diagnosis.
  • Sepsis: Given the patient's age, the presence of a potential infection source (the wound), and the report of a chill, sepsis must be considered and promptly evaluated for.
  • Gas Gangrene: Another rare but potentially deadly condition that could arise from a traumatic wound, especially if the wound became contaminated.
• Rare diagnoses
  • Pyoderma Gangrenosum: A rare skin condition that can mimic an ulcer or infection but has a distinct appearance and may not respond to typical antibiotic treatments.
  • Vasculitis: Inflammation of the blood vessels that could present with skin lesions and systemic symptoms, though this would be less likely given the patient's presentation.

Recommended Labs and Tests

Given the differential diagnosis, the following labs and tests are recommended:

• Complete Blood Count (CBC) with differential to evaluate for signs of infection or inflammation.
• Blood cultures to rule out sepsis.
• Basic Metabolic Panel (BMP) to assess renal function and electrolyte balance.
• Coagulation studies (PT/INR, aPTT) to evaluate for any coagulopathy that might contribute to the patient's condition.
• Lower extremity Doppler ultrasound to evaluate for DVT.
• Wound culture to guide antibiotic therapy if an infection is present.
• Consider imaging studies (e.g., X-ray, MRI) if there's suspicion of osteomyelitis, gas gangrene, or necrotizing fasciitis, though these would be guided by clinical findings and initial lab results.