Differential Diagnosis

• Single most likely diagnosis:
  • Fournier's gangrene: This condition is characterized by necrotizing fasciitis of the genitalia, which matches the patient's presentation of a large eschar on the scrotum, purulent fluid, and crepitus. The patient's history of diabetes and immunocompromised state due to HIV also increase the risk for this condition.
• Other Likely diagnoses:
  • Necrotizing fasciitis: While this is a broader category that includes Fournier's gangrene, the presence of air tracking along fascial planes and crepitus suggests necrotizing fasciitis. The patient's symptoms and lab results, such as a high WBC count and low blood pressure, also support this diagnosis.
  • Severe cellulitis or abscess: Although less likely given the presence of crepitus and air on CT, severe cellulitis or an abscess could still be considered, especially if the patient's symptoms were less severe.
• Do Not Miss diagnoses:
  • Septic shock: The patient's low blood pressure, high heart rate, and elevated WBC count suggest septic shock, which is a life-threatening condition that requires immediate attention.
  • Testicular torsion: Although less likely given the patient's presentation, testicular torsion is a surgical emergency that can cause severe pain and should not be missed.
• Rare diagnoses:
  • Gas gangrene: This condition, caused by Clostridium perfringens, can cause similar symptoms to necrotizing fasciitis, including crepitus and air on imaging. However, it is less common and typically associated with trauma or surgical wounds.
  • Syphilis or other sexually transmitted infections: Although the patient's symptoms are not typical for these conditions, it is essential to consider them in the differential diagnosis, especially given the patient's HIV status.