Differential Diagnosis

• Single most likely diagnosis
  • Ecchymosis due to anticoagulation (ASA): The patient is taking ASA (aspirin) twice daily following a recent knee replacement surgery, which increases the risk of bruising due to its anticoagulant effect. The absence of trauma history and the presence of a bruise in a location that could be subject to minor, unnoticed trauma or pressure (such as from a walker or during physical therapy) supports this diagnosis.
• Other Likely diagnoses
  • Trauma (unnoticed or minor): Despite the patient's denial of injury, it's possible that a minor trauma occurred, especially considering the patient's use of a walker and participation in physical therapy, which could lead to unnoticed bumps or pressures against the breast area.
  • Senile purpura: This condition is characterized by easy bruising and is common in older adults due to age-related changes in the skin and blood vessels. However, the location and description might not fully align with typical presentations of senile purpura.
• Do Not Miss (ddxs that may not be likely, but would be deadly if missed)
  • Breast cancer: Although the patient has a recent mammogram reported as up-to-date, any new breast finding warrants consideration of malignancy, especially if there are any changes or if the bruise does not resolve as expected.
  • Hematoma (possibly related to a bleeding disorder or anticoagulant use): While the patient is on ASA, which increases the risk of bleeding, a hematoma could be a more significant collection of blood that might require intervention.
  • Inflammatory breast cancer: This rare but aggressive form of breast cancer can present with skin changes, including bruising or discoloration, and is a critical diagnosis not to miss due to its poor prognosis if not treated promptly.
• Rare diagnoses
  • Fat necrosis: This condition can occur after trauma to the breast tissue and might present with a palpable mass or skin changes, including bruising. It's less likely given the absence of a reported significant trauma but could be considered if the bruise does not resolve or changes over time.
  • Sickle cell crisis or other hematologic disorders: If the patient has an underlying condition affecting blood cells or clotting, this could potentially lead to bruising. However, these conditions would likely have been previously diagnosed or suggested by other symptoms.