Differential Diagnosis for a High Lesion on the Finger

• Single most likely diagnosis
  • Herpes simplex infection: This is a common condition that can cause painful, fluid-filled blisters or lesions on the fingers, often referred to as herpetic whitlow. The location and description of the lesion on the finger make this a plausible diagnosis.
• Other Likely diagnoses
  • Paronychia: An infection around the nail, which can cause redness, swelling, and sometimes a pus-filled lesion. Given the location "on the finger," this could be a likely consideration, especially if the lesion is near the nail.
  • Felon: A type of abscess that occurs on the fingertip pads, caused by bacterial infection. It presents as a painful, swollen lesion and could be considered given the description.
  • Wart: Caused by the human papillomavirus (HPV), warts can appear anywhere on the skin, including the fingers. They might be considered if the lesion is hard and rough.
• Do Not Miss (ddxs that may not be likely, but would be deadly if missed.)
  • Erysipelas: A type of skin infection that can spread rapidly and involves the upper dermis, typically caused by beta-hemolytic group A Streptococcus. It requires prompt antibiotic treatment to prevent serious complications.
  • Cellulitis: A bacterial skin infection that can cause redness, swelling, and pain. If not treated, it can lead to more serious conditions.
  • Gas gangrene: Although rare, this is a potentially life-threatening condition caused by Clostridium perfringens. It can start as a small, painful lesion but rapidly progresses.
• Rare diagnoses
  • Anthrax: A rare but potentially deadly infection caused by Bacillus anthracis. Cutaneous anthrax can present as a lesion that eventually turns into a black eschar.
  • Sporotrichosis: A fungal infection caused by Sporothrix schenckii, which can cause lesions on the skin, especially after exposure to contaminated soil or plants. It's more common in gardeners or those who work with plants.