Differential Diagnosis for a 60-year-old Female with a Red, Tender, and Warm Area on the Posterior Knee
- Single most likely diagnosis:
- Cellulitis: This is the most likely diagnosis given the patient's symptoms of a red, tender, and warm area on the posterior knee, which has increased in size over the past week. The absence of a specific injury or bite and the onset after gardening suggest a possible bacterial infection, which is consistent with cellulitis.
- Other Likely diagnoses:
- Contact dermatitis: Although the patient does not report pruritus, contact dermatitis could still be a possibility, especially if she came into contact with an allergen or irritant while gardening.
- Folliculitis: This is an inflammation of the hair follicles, which could be caused by bacterial or fungal infections. The patient's symptoms of tenderness and warmth to touch could be consistent with folliculitis.
- Insect bite or sting: Although the patient does not remember any specific bites or stings, it is possible that she was bitten or stung while gardening, which could have caused the redness and swelling.
- Do Not Miss (ddxs that may not be likely, but would be deadly if missed.):
- Necrotizing fasciitis: This is a rare but life-threatening condition that requires prompt medical attention. Although it is unlikely, the patient's symptoms of tenderness, warmth to touch, and increasing redness could be consistent with necrotizing fasciitis.
- Abscess: A skin abscess could be a possible diagnosis, especially if the patient has a history of bacterial infections. An abscess could be life-threatening if left untreated, especially if it becomes infected with a more virulent bacteria.
- Septic arthritis: Although the patient does not report any joint pain or swelling, septic arthritis is a possible diagnosis that should not be missed. This condition requires prompt medical attention to prevent long-term joint damage.
- Rare diagnoses:
- Erysipelas: This is a type of bacterial infection that affects the upper layer of the skin. Although it is rare, the patient's symptoms of redness, tenderness, and warmth to touch could be consistent with erysipelas.
- Sporotrichosis: This is a rare fungal infection that can be caused by contact with contaminated soil or plants. Although it is unlikely, the patient's symptoms and history of gardening could be consistent with sporotrichosis.