What is the diagnosis and management for a 65-year-old female with a history of non-STEMI, cardiomyopathy, CKD, seizure disorder, pneumonia, and COPD, presenting with signs of cellulitis and impaired oxygen saturation on room air, and non-adherence to medications?

Differential Diagnosis

• Single most likely diagnosis
  • Cellulitis: The patient presents with increasing lower extremity redness, swelling, and discomfort inferior to the cat scratch site over the past 2 weeks. This is a classic presentation for cellulitis, a common bacterial skin infection that can occur after a break in the skin, such as a cat scratch.
• Other Likely diagnoses
  • Abscess: Given the history of a cat scratch and the development of localized redness, swelling, and discomfort, an abscess (a collection of pus) could be a possible diagnosis, especially if the infection has localized.
  • Deep Vein Thrombosis (DVT): The patient has a history of recent hospitalization, immobility, and chronic conditions such as cardiomyopathy and COPD, which increase her risk for DVT. The swelling and discomfort in her lower extremity could be indicative of a DVT.
  • Erythema migrans (Lyme disease): Although less common, the patient's exposure to a cat scratch and subsequent development of a rash could potentially be related to Lyme disease, especially if the cat had been in contact with ticks.
• Do Not Miss (ddxs that may not be likely, but would be deadly if missed.)
  • Necrotizing fasciitis: This is a severe infection of the skin and soft tissues that can rapidly progress and is life-threatening. The patient's symptoms of increasing redness, swelling, and discomfort, especially in the context of a recent break in the skin, necessitate consideration of this diagnosis.
  • Sepsis: Given the patient's complex medical history, including recent pneumonia and the current signs of infection (redness, swelling, and decreased oxygen saturation), sepsis is a critical diagnosis not to miss.
  • Pulmonary embolism: The patient's history of recent immobility, cardiomyopathy, and COPD, along with her decreased oxygen saturation, makes pulmonary embolism a diagnosis that should be considered to avoid missing a potentially fatal condition.
• Rare diagnoses
  • Cat-scratch disease (Bartonellosis): Although the patient was scratched by a cat, cat-scratch disease typically presents with a papule or pustule at the site of the scratch, followed by regional lymphadenopathy, which is not described in this scenario.
  • Ecthyma: A deeper skin infection that can occur after a break in the skin, ecthyma could be considered but is less likely given the description of the patient's symptoms.