Differential Diagnosis for a Superficial Lesion on the Patella

• Single most likely diagnosis:
  • Prepatellar bursitis: This condition, also known as housemaid's knee, is an inflammation of the bursa in front of the patella. It's common in individuals who frequently kneel, making it a likely diagnosis for a superficial lesion on the patella that is not big.
• Other Likely diagnoses:
  • Sebaceous cyst: A benign, usually mobile, lump under the skin that can appear anywhere, including the patella area. It's superficial and can be small, fitting the description.
  • Lipoma: A benign tumor composed of fat tissue. It can occur almost anywhere in the body, including the skin over the patella, and is typically superficial and small.
  • Dermatofibroma: A small, hard bump on the skin that typically develops following a minor injury, most often on the legs. It's superficial and not large, making it a plausible diagnosis.
• Do Not Miss diagnoses:
  • Skin cancer (e.g., basal cell carcinoma, squamous cell carcinoma): Although less likely, skin cancers can present as small, superficial lesions. Given the potential severity of missing such a diagnosis, it's crucial to consider and rule out malignancy.
  • Infection (e.g., abscess, cellulitis): An infection in the skin over the patella could present as a superficial lesion. While it might not be the first consideration, missing an infection could lead to serious consequences, including spread of the infection.
• Rare diagnoses:
  • Xanthoma: A rare skin growth that can appear as a small, superficial lesion. It's associated with lipid disorders and is less common but should be considered in the differential diagnosis for completeness.
  • Ganglion cyst: Typically found on the wrist but can occur near other joints, including the knee. It's less common on the patella but could present as a small, superficial lump.