Differential Diagnosis

• Single most likely diagnosis
  • Foreign body reaction or residual fragment: The patient's history of having something removed from their foot after stepping on a rock in the sea suggests that there might be a residual fragment or a reaction to a foreign body, leading to the stabbing pain.
• Other Likely diagnoses
  • Sea urchin spine injury: Stepping on a sea urchin can cause spine fragments to break off into the skin, leading to pain, swelling, and potentially infection.
  • Infection (e.g., cellulitis, abscess): Introduction of bacteria into the wound from the sea or the object that pierced the skin could lead to infection, which might cause pain, redness, and swelling.
  • Partial thickness wound or bruising: The initial injury could have caused a partial thickness wound or significant bruising, which might still be causing pain two months later, especially if the wound was deep or if there was significant tissue damage.
• Do Not Miss (ddxs that may not be likely, but would be deadly if missed.)
  • Tetanus infection: Although less common, especially in individuals who are up to date with their tetanus vaccinations, tetanus infection can occur from wounds contaminated with tetanus spores, which are found in soil and possibly in sea environments.
  • Marine-related infections (e.g., Vibrio vulnificus): Certain bacteria found in marine environments can cause severe infections, especially in individuals with compromised immune systems.
  • Osteomyelitis: A bone infection that could result from the initial puncture wound, especially if the object that entered the foot was contaminated with bacteria.
• Rare diagnoses
  • Erysipeloid: A rare infection caused by Erysipelothrix rhusiopathiae, which can be acquired from contact with infected animals or contaminated water.
  • Marine puncture wound with exotic pathogens: Depending on the location and specific conditions of the injury, there could be a risk of infection with less common pathogens found in marine environments.