Differential Diagnosis for Atraumatic, Sudden Onset Dorsolateral Foot Pain

• Single Most Likely Diagnosis
  • Cellulitis: The initial presentation of sudden onset dorsolateral foot pain with pitting edema, warmth, and erythema, which responded to Keflex (an antibiotic), suggests a bacterial infection such as cellulitis. The fact that the erythema responded to antibiotics supports this diagnosis, although the persistence of localized pitting edema and pain with dorsal flexing may indicate a complicating factor or an additional diagnosis.
• Other Likely Diagnoses
  • Deep Vein Thrombosis (DVT): The presence of pitting edema, warmth, and pain, especially with dorsal flexing, could suggest a DVT. The fact that some symptoms persisted despite antibiotic treatment for cellulitis makes DVT a plausible consideration.
  • Tendinitis or Tenosynovitis: Inflammation of the tendons or their surrounding sheaths on the dorsolateral aspect of the foot could cause pain, especially with movement like dorsal flexing. This could be related to or exacerbated by the initial infection.
  • Gout or Pseudogout: These conditions can cause sudden onset of pain, swelling, and erythema, typically in a joint. However, the response to antibiotics and the specific location might make these less likely, though not impossible.
• Do Not Miss Diagnoses
  • Osteomyelitis: A bone infection that could result from an initial soft tissue infection like cellulitis. It's crucial to consider this, especially if the patient has risk factors for osteomyelitis or if symptoms persist or worsen despite appropriate antibiotic treatment.
  • Septic Arthritis: An infection within a joint, which is a medical emergency. The sudden onset of pain, swelling, and erythema, along with the specific location on the foot, necessitates consideration of this diagnosis, especially if the patient has a fever or other systemic signs of infection.
  • Compartment Syndrome: A condition resulting from increased pressure within a muscle compartment, which can lead to muscle and nerve damage. It's less likely given the description but should be considered, especially if pain is severe and out of proportion to what is expected.
• Rare Diagnoses
  • Erythromelalgia: A disorder characterized by burning pain, heat, and redness in the hands and feet. It's less common and might not fully explain the initial response to antibiotics but could be considered if other diagnoses are ruled out.
  • Complex Regional Pain Syndrome (CRPS): A condition characterized by persistent burning pain and inflammation following an injury, which could potentially be triggered by an infection. It's rare and the diagnosis would require further evaluation for characteristic signs like allodynia or changes in skin temperature and color.