Differential Diagnosis for a Swollen Thumb

Given the symptom of a swollen thumb, we must consider various potential causes, categorizing them based on their likelihood and the urgency of diagnosis.

• Single Most Likely Diagnosis

  • Cellulitis: This is an infection of the skin and subcutaneous tissues, which can cause swelling, redness, and warmth in the affected area. The thumb being "very swollen" aligns with symptoms of cellulitis, especially if there's a history of trauma or infection in the area.

• Other Likely Diagnoses

  • Insect bite or sting: Certain insect bites can cause significant swelling, especially if there's an allergic reaction.
  • Trauma: A recent injury to the thumb could lead to swelling due to inflammation or hematoma.
  • Gout or pseudogout: These conditions can cause sudden, severe swelling in joints, including those in the thumb.

• Do Not Miss Diagnoses

  • Deep Vein Thrombosis (DVT): Although less likely in the thumb specifically, DVT in the arm (if the swelling extends beyond the thumb) is a critical diagnosis not to miss due to its potential for pulmonary embolism. However, DVT typically presents with swelling, pain, and discoloration in the entire limb rather than localized to the thumb.
  • Septic arthritis: An infection within a joint, which could potentially occur in the thumb, is a medical emergency requiring prompt treatment.
  • Compartment syndrome: A condition resulting from increased pressure within a confined space in the body, which can lead to muscle and nerve damage. It's less common in the thumb but could occur after severe trauma.

• Rare Diagnoses

  • Erythema nodosum: A type of skin inflammation that could cause swelling but is less common and typically presents on the lower legs.
  • Sarcoidosis: A condition that can cause swelling and inflammation in various parts of the body, including the skin, but is relatively rare.
  • Tumor: Either benign or malignant, tumors can cause localized swelling but would be an uncommon cause of acute thumb swelling.