Differential Diagnosis for Inflamed Left Ankle

• Single most likely diagnosis
  • Cellulitis: Given the presentation of non-pitting swelling, inflammation, rash, and an open macule eraser-sized lesion on the ankle, cellulitis is a strong consideration. The patient's history of being on her feet for 8 hours a day increases the risk of skin breakdown and infection. The absence of discharge and the description of the lesion support this diagnosis.
• Other Likely diagnoses
  • Eczema/Dermatitis: The presence of a rash and inflammation could suggest eczema or dermatitis, especially if the patient has a history of skin allergies or irritants.
  • Stasis Dermatitis: Given the patient's age and occupation, which involves standing for long periods, stasis dermatitis is a possibility. This condition is characterized by skin inflammation and discoloration due to poor circulation.
  • Contact Dermatitis: This could be a reaction to something the patient's skin has come into contact with, such as a new soap, detergent, or even certain components of her footwear.
• Do Not Miss (ddxs that may not be likely, but would be deadly if missed.)
  • Deep Vein Thrombosis (DVT): Although the presentation does not strongly suggest DVT, the patient's age, history of rheumatoid arthritis (RA), and prolonged periods of standing increase her risk. DVT can present with swelling and inflammation of the leg, making it a critical diagnosis not to miss due to its potential for severe complications, including pulmonary embolism.
  • Necrotizing Fasciitis: This is a severe infection that can start with similar symptoms but rapidly progresses. It's less likely but critical to consider due to its high mortality rate if not promptly treated.
• Rare diagnoses
  • Pyoderma Gangrenosum: A rare skin condition that can cause painful ulcers, which might resemble the described lesion. It's often associated with systemic diseases like RA, which the patient has.
  • Erythema Nodosum: This condition causes red nodules under the skin, typically on the shins, and can be associated with various systemic conditions, including infections and autoimmune diseases like RA.

The treatment with mupirocin and chlorhexidine is appropriate for managing the skin infection. However, further evaluation and possibly adjusting the treatment plan based on the patient's response and the progression of symptoms may be necessary.